ALBERT

Notes: Summary The systemic availability of a new antidepressant, zimelidine, and of its pharmacologically active metabolite, norzimelidine, was studied in six healthy male volunteers. Three single doses of zimelidine (25 mg and 100 mg orally and 25 mg i.v.) and two single doses of norzimelidine (25 mg orally and i. v.) were given to each volunteer allowing at least seven days between administrations. Plasma concentrations of zimelidine and norzimelidine were determined in serial blood samples by HPLC. Following oral zimelidine peak plasma concentrations of the metabolite were attained about 3 h after dosing. Oral administration of norzimelidine itself resulted in a plasma concentration profile for this compound that was similar to that observed after oral zimelidine. Utilising the plasma concentration data following intravenous infusion of each compound, the elimination half-lives for zimelidine and norzimelidine were calculated to be 5.1 h (range 4.3–6.0) and 15.5 h (range 10.6–22.9) respectively. The total body clearances of the 2 compounds were similar at 0.52 l · min−1 (range 0.26–0.70) for zimelidine and 0.56 l · min−1 (range 0.28–0.83) for norzimelidine. The substantially longer elimination half-life of norzimelidine was apparently the result of a larger volume of distribution (9.4 l · kg−1; range 7.8–11.4) for this metabolite, as compared to zimelidine (3.21 · kg−1; range 1.6–4.9). The calculated bioavailability of zimelidine was 26% (range 9.1–39) after the 25 mg oral dose, and 29% (range 14–46) after the 100 mg dose. The bioavailability of norzimelidine was 66% (range 36–91). However, oral administration of zimelidine resulted in as much or more norzimelidine reaching the systemic circulation, as the oral administration of norzimelidine itself. This is important as a large part of the activity of the drug may be due to the metabolite.

Notes: Summary The pharmacokinetics of pyridostigmine was evaluated after intravenous injection in two healthy male volunteers and after oral administration to five subjects. Plasma concentrations of pyridostigmine were determined after ion pair extraction from plasma and analysis by gas chromatography — mass spectrometry with chemical ionization, using d6-pyridostigmine as internal standard. Degradation of pyridostigmine in vitro was compensated for by use of the deuterated internal standard and by rapid cooling and separation of plasma after blood sampling. After intravenous administration of pyridostigmine 2.5 mg the plasma elimination half-life was 1.52 h, the volume of distribution was 1.43 l/kg and the plasma clearance 0.65 l/kg × h. The pharmacokinetic constants were very similar after oral administration of pyridostigmine 120 mg; the elimination half-life was 1.78±0.24 h, the volume of distribution 1.64±0.29 l/kg and the plasma clearance was 0.66±0.22 l/kg × h. The bioavailability was calculated to be 7.6±2.4%. When pyridostigmine was taken together with food, the time to reach the peak plasma concentration was prolonged from 1.7 to 3.2 h. Bioavailability, however, was not influenced by concomitant food intake. “Steady-state” plasma concentrations of pyridostigmine were measured in myasthenic patients on their ordinary dose schedule of cholinesterase inhibitor drugs. More than a seven-fold difference in steady-state plasma concentration was found between patients taking approximately the same daily dose of pyridostigmine.

Notes: Summary Plasma concentrations of orphenadrine were measured by a specific gaschromatographic method in 5 healthy male volunteers after a single oral dose of orphenadrine hydrochloride 100mg. The single dose pharmacokinetic profile of orphenadrine was evaluated from these data. The elimination half-life ranged from 13.2–20.1 h after the commercial tablet formulation. Plasma concentrations, determined in volunteers and patients under different conditions of repeated oral administration of the same formulation of orphenadrine hydrochloride exceeded the theoretical values, predicted from the single dose pharmacokinetics, by a factor 2 to 3. The elimination half-lives after discontinuation of treatment showed a 2 to 3-fold increase over the single dose values. This demonstrates a clear discrepancy between the multiple and single dose pharmacokinetics of orphenadrine. Experiments in dogs suggested competition for biotransformation between orphenadrine and its metabolite N-demethylorphenadrine. Product inhibition of this type could explain the observed discrepancy.

Notes: Summary Two formulations of indapamide tablets (2.5 mg) were given as a 5.0 mg dose and the subsequent blood levels were compared to those obtained after administration of a 5.0 mg solution. The study was conducted as a randomized three-way crossover design using healthy male volunteers. The drug was well tolerated by all the subjects involved. The area under the blood concentration versus time curve, extrapolated to infinity was essentially the same for all three formulations (4.2, 4.7, and 4.4 µg-h/ml). Statistical comparison of the blood levels from the two tablets showed that one tablet had a significantly greater maximum blood concentration (263 vs 231 ng/ml) and a significantly shorter time of maximum blood concentration (2.3 vs 3.5 h). Cmax (333 ng/ml) and tmax (0.7 h) values for the solution were significantly higher than either tablet. The average half-life (β-phase) for all three formulations was 15 h, while the average systemic clearance was 20 ml/min. Indapamide has a low clearance rate and there was no evidence that the drug undergoes a first-pass effect.

Notes: Summary 21 healthy women undergoing gynaecological operations received rectal premedication with morphine 0.3 mg/kg body weight. Plasma concentrations of morphine were followed for 4 h by a GC/MS technique. In most patients the peak plasma concentration was reached after 30 min; the mean peak plasma level of morphine was 18 ng/ml (range 8.5–57 ng/ml). The bioavailability of rectal morphine was determined in 6 patients, who received an i.m. injection of morphine at a second operation. The mean bioavailability of rectal morphine was 31% (range 12%–61%). None of the patients showed any clinical sign of respiratory depression, and there was no increase in end-tidal carbon dioxide tension measured in 5 patients operated under spinal block.

Notes: Summary The kinetics of ergotamine has been investigated in migrainous patients using a new, specific, sensitive HPLC assay (detection limit 100 pg/ml plasma). 10 patients were given ergotamine tartrate 0.5 mg i.v. and 5 of them received the same dose i.m. 2–3 weeks later. Blood samples were collected for up to 54 h following administration and the plasma concentration were analysed. After intravenous administration the plasma ergotamine declined rapidly, with an initial distribution half-life of 3 min followed by a mean terminal half-life of 1.86 h (range 90–155 min). The mean total plasma clearance was 11.0 ml kg−1 min−1, and the volume of distribution (Vdβ ) was 1847.6 ml kg−1. Individual t1/2β showed a positive linear correlation with the individual Vdβ . The intramuscular absorption of ergotamine was rapid and maximum plasma levels were usually obtained 10 min following administration. The biological availability was incomplete and variable at 46.6% (range 28.3–60.8%).

Notes: Summary Previous studies have shown that aspirin interacts with orally administered diclofenac sodium, causing reduced peak concentrations, lower levels and decreased areas under curves. In this study, diclofenac sodium was administered orally and intravenously with and without aspirin, to 6 healthy female volunteers. After intravenous dosing both plasma levels and areas under curves were significantly reduced although none of the rate constants was affected. The volume of distribution of diclofenac was increased as was the plasma clearance. Oral administration with aspirin also resulted in lower plasma levels, particularly peak levels, and areas under curves. Comparison of AUC's for both modes of administration with and without aspirin suggested that lower levels after oral administration were not due to impaired absorption. These observations are best explained by decreased protein binding and increased biliary excretion of diclofenac in the presence of salicylate.

Notes: Summary Rectal and oral absorption of valproic acid and its sodium salt by man were compared to explore the possibility of rectal administration of the drug. The plasma concentration of valproic acid was measured by gas chromatography after a single oral dose of sodium valproate 600 mg, and after single rectal doses of sodium valproate 600 mg and valproic acid 520 mg, in a cross-over study in 7 volunteers. The rectal dosage forms included fatty suppositories and aqueous solutions. Compared with oral administration, rectal absorption of sodium valproate from an aqueous micro-enema was fast and complete. The free acid was absorbed more rapidly from fatty suppositories than was the sodium salt. The absorption rate from the rectum increased with the dose of valproic acid. Both findings are consistent with a diffusion — absorption mechanism based on the pH-partition hypothesis. Differences in the chemical composition of the fatty suppository base were not reflected in differences in absorption rate and relative bioavailability. No essential difference in absorption rate was observed if volunteers remained lying or sitting during the experiment. Rectal dosing with valproic acid 520 mg dissolved in 4 ml suppositories, twice a day resulted in steady-state plasma concentrations of 50 to 100 µg · ml−1, within the therapeutic range.

Notes: Summary Variation in the systemic disposition of theophylline after ingestion of a new microcrystalline product (Theolair®) has been investigated in 7 hospitalized patients with generalized obstructive lung disease. Disposition (absolute bioavailability) was determined by comparing in the same patients the areas under the serum concentration-time curves after a single oral dose of microcrystalline theophylline and after an intravenous infusion of aminophylline. Oral absorption appeared to be fast. The half-life of absorption was 19±9 min (mean±SD). Maximal serum concentrations reached after 100±30 min were found to be in a rather narrow range: 9.8±2.5 mg · 1−1. The absolute bioavailability of the microcrystalline preparation was high and it showed only small variation: 102.7±10.2% of the dose. Relevant pharmacokinetic parameters (half-life of elimination, volume of distribution and total body clearance) were determined after both routes of administration. Individual dosage regimens required to obtain a therapeutic serum concentration were calculated for each individual patient on the basis of the observed pharmacokinetic parameters.

Notes: Summary The pharmacokinetic parameters of deacetyl metipranolol were determined after i.v. infusion of increasing doses (6–25 mg) in 17 normal volunteers. In a second cross-over trial, deacetyl metipranolol 10 and 20 mg were infused in a further 10 subjects, and in a third trial another 20 volunteers received metipranolol 40 mg orally. Metipranolol is very rapidly and completely deacetylated in man, so all pharmacokinetic data refer to deacetyl metipranolol, which was assayed by gas chromatography-mass spectrometry. The pharmacokinetic analysis was performed using a recently developed model, using a volume of distribution which is variable with time. The following data were obtained after oral administration: (mean values); lag-time 7.3 min; tmax 50 min, invasion half-life 6.3 min; elimination half-life 3 h; urinary excretion of unchanged drug approximately 4% of the dose. The experiments with infusion of increasing doses, as well as the cross-over study with 10 and 20 mg i.v., showed dose-linearity of the kinetics. The respective mean half-lives of elimination were 2.6, 2.9 and 2.8 h. The mean total, renal and extra-renal clearances amounted to 1237 ml/min, 149 ml/min and 1068 ml/min, respectively. The distribution coefficient was 3.5 l/kg, and protein binding amounted to 70% within the range of therapeutic concentrations. Absolute bioavailability was found to be approximately 50% by several different evaluation procedures. Thus, the pharmacokinetic profile of metipranolol shares features of both the lipophilic and the hydrophilic groups of β-blocking agents.

Notes: Summary 16 premature infants suffering from neonatal apnoea received orally an aqueous solution of theophylline 5 mg/kg bodyweight under fasting conditions and immediately before a milk feed. Bioavailability up to 7 h after administration was determined from the serum concentration-time course. The rate of absorption was significantly decreased if the drug was given with food; mean maximum serum concentrations were reached after 4.7 h instead of 1.6 h under fasting conditions. The area under the curve did not differ between the two patient groups which indicates that only the rate but not the amount of absorption was affected by food intake. The influence of feeding on the rate of absorption of theophylline by premature infants, which is more pronounced than in adults, can be related to particular functional factors in the gastrointestinal tract during the neonatal period.

Notes: Summary Acetylsalicylic acid (ASA) is a strong, irreversible inhibitor of platelet aggregation, but loses this activity following first-pass deacetylation to salicylic acid (SA). In order to compare the bioavailability of unchanged ASA from rapid- and slow-release formulations, the single-dose concentration profiles of ASA and SA were studied in healthy volunteers following intake of two different rapid-release (conventional and effervescent tablets) and three different slow-release (microencapsulated ASA in tablets and in capsules, and enteric-coated tablets) formulations of ASA, and of one slow-release formulation of sodium salicylate. Since anti-platelet therapy with ASA is often combined with dipyridamol, the influence of this drug was also examined. The concentrations of ASA and SA were measured by high-pressure liquid chromatography. While the bioavailability of SA from the 5 ASA formulations was essentially equal and similar to that of the salicylate formulation, the bioavailability and peak concentrations of ASA appeared to be the much greater after rapid-release than after slow-release formulations. Indeed, ASA was only rarely detected in systemic blood following intake of slow-release ASA. Co-administered dipyridamol did not significantly influence the kinetics of ASA or SA. It appears that rapid-release formulations of ASA should be prefered in anti-platelet therapy, either alone or in combination with dipyridamol.

Notes: Summary For drugs with a high hepatic clearance, bioavailability is low due to the so-called “first pass effect”. Prediction of the bioavailability for these drugs has been only lossely tested. It is proposed that by plotting the reciprocal of bioavailability versus the oral clearance, a straight line with intercept of unity and slope of reciprocal of hepatic blood flow should ensue. For lignocaine and verapamil, this relationship was found to be strong and gave good predictability, whereas for propranolol this relationship was weak and gave poor predictability. The proposed method may be of value in determining whether the low bioavailability of a drug is due to hepatic first pass metabolism.

Notes: Summary High oral doses of mebendazole are used experimentally for the treatment of human alveolar and cystic echinococcosis. In order to assess bioavailability of this drug 1.5 g doses were given to 3 volunteers. Measurable plasma concentrations of 17 to 134 nmol/l were found only if mebendazole was given together with a fatty meal. In a patient with cholestasis plasma concentrations were higher than in the 3 normal subjects. In patients on long term treatment the increase in plasma concentration after administration of a 1 g dose varied between 0 and 500 nmol/l. It is concluded that systemic availability of mebendazole is enhanced by concomitant food intake. In view of the large intra- and interindividual variation in plasma concentration, monitoring plasma levels during long term therapy appears advisable.

Notes: Summary The relative bioavailability of a new paracetamol suppository (Panodil) and tablets in doses of 0.5 and 1 g was investigated in eight healthy subjects. The tablets were absorbed faster and higher peak plasma concentrations were obtained than after the suppositories. The bioavailability of the suppositories was approximately 80% of that of the tablets at both dose levels. There was no indication of capacity-limited elimination at either the two doses investigated.

Notes: Summary Plasma and urinary levels of chlorpheniramine (CPM) and its 2 demethylated metabolites were measured by HPLC after i.v. and oral dosing. In 5 mg (maleate) i.v. bolus studies in 2 subjects, plasma CPM levels were fitted to triexponential equations with terminal half-lives (t 1/2) of 23 and 22 h and area of 3.6 and 3.21/kg, respectively. Intravenous data predicted hepatic blood extraction ratios for the 2 subjects to be 0.06 and 0.07, respectively. Absolute bioavailability from oral solution (10 mg) was 59 and 34%, and from tablets (8 mg) 44 and 25%, respectively, indicating extensive gut first-pass metabolism. Mean t 1/2 from 7 oral fasting studies in 5 subjects was 28 h (19–43 h). Mean absorption lag time was 0.7 h (0.4–1.3 h), and mean peak time was 2.8 h (2–4 h). In 2 subjects, 6 mg solutions were given every 12 h for 9 doses; good correlation between single and multiple dose kinetics was found. Significant accumulation was demonstrated in simulation studies with frequent daily dosing. Estimated accumulation ratios vary from 4.1 to 9.4 (mean 6.5). The t 1/2 from urinary data (collected for 12 days) was consistent with plasma data. The above results suggest the need to reexamine the current practice of frequent daily dosing and the use of sustained or controlled release dosage forms of this drug. The possible cause of reduced plasma clearance of CPM in renal patients is discussed.

Notes: Summary The effect of food on the rate and extent of absorption of tolbutamide in diabetic patients was studied by varying the time of drug administration in relation to the ingestion of a standard meal. Serum levels of tolbutamide, insulin and glucose and related bioavailability parameters were compared following the administration of a single dose of tolbutamide 0.5 g to diabetic patients 30 min prior to and immediately before a standardized meal. A placebo dosage form was also administered to determine baseline glucose and insulin response to the meal. The 700 calorie standard meal was composed of 41% carbohydrate, 18% protein, and 41% fat. Administration of the drug with the meal resulted in a 6% (statistically significant) decrease in the extent of absorption, as determined by measurement of the area under the tolbutamide serum level-time curve from zero to infinity. Serum levels of tolbutamide were also significantly higher 0.5 h after drug administration when the drug was taken with the meal. Except for these two minor effects, no other differences between the drug treatments were observed in any other parameters of tolbutamide absorption or in the postprandial glucose and insulin serum levels. Therefore, the small differences found were judged to be clinically meaningless. These findings demonstrate that administration of tolbutamide 0.5 g tablets 30 min prior to or with a standard meal results in equivalent therapeutic actions.

Notes: Summary The kinetics of phenobarbital (PB) were evaluated in six normal subjects and six epileptic patients treated with phenytoin or carbamazepine. Each normal subject received three single doses of PB: PB-sodium 130 mg i.v. (IV), PB sodium 130 mg i.m. (IM), and PB acid 100 mg orally (PO), in random order at least one month apart. After IV PB distributive half-lives varied from 0.13 to 0.70 h, disposition half-lives were 75 to 126 h, steady state volume of distribution (Vss) was 0.54±0.03 l/kg, and clearance (CL) was 3.8±0.77 ml/h/kg. Absolute bioavailability of IM PB was 101±13%, of PO PB (corrected for dose) 100±11%. Peak serum PB concentrations were achieved from 2 to 8 h after IM administration, and from 0.5 to 4 h after PO administration. Epileptic patients exhibited similar PB kinetics: disposition half-lives were 77 to 128 h, Vss 0.61±0.05 l/kg, and Cl 3.9±0.76 ml/h/kg. Phenobarbital appears to represent an exception among antiepileptic drugs, in that pharmacokinetic data obtained in normals can reasonably be extrapolated to the epileptic population.

Notes: Summary The bioavailability of chloroquine in 7 healthy adult male volunteers was assessed with and without a standard breakfast. Chloroquine (600 mg base) was administered orally and timed blood samples were obtained for determination of plasma concentrations. The results suggest that the AUC and peak plasma levels were significantly higher when chloroquine was administered together with food, although the rate of absorption was not different. It appears, therefore, that food facilitates chloroquine absorption and the extent of absorption is significantly modified. Hence administration of chloroquine together with food appears to be an advisable clinical practice.

Notes: Summary 7-3H-phenylephrine was given to 15 volunteers by a short-infusionn=4) or p.o. (10 volunteers, 1 patient with porto-caval anastomosis). Analysis of serum for free3H-phenylephrine and fractionation of urinary radioactivity was performed by ion-exchange and thin-layer chromatography. As almost the same3H-activity was excreted in urine after i.v. and p.o. administration, 86% and 80% of the dose respectively, complete enteral absorption can be assumed. A considerable difference was seen in the fraction of free phenylephrine, i.v. 16% of the dose versus p.o. 2.6%, which suggested reduced bioavailability. This was confirmed by comparison of the areas under the serum curve, which showed a bioavailability factor of 0.38. The result for the patient with porto-caval anastomosis was comparable to that in the normal volunteers. The biological half-life of 2 to 3h was comparable to that of structurally related amines, as were the total clearance of 2 1/h, and the volume of distribution of 340l. Metabolism to phenolic conjugates mainly after oral ingestion, and tom-hydroxymandelic acid after i.v. injection, again demonstrated thatm-hydroxylated amines are predominantly conjugated during the “first-pass” metabolism.

Notes: Summary Plasma concentrations and bioavailability of disopyramide following repeated administration of standard capsules and controlled-release tablets have been compared. Ten patients were randomized into two groups; Group I received disopyramide capsules 150 mg every 6 h for five days and subsequently disopyramide controlled-release tablets 300 mg every 12 h for further five days. Group II received the same preparations in the reverse order. There was a more rapid rise in disopyramide concentration after the capsules: the maximum of 10.7±0.6 µmol/l (mean ± SEM) was reached within 1.8±0.4 h as compared to 10.6±0.4 µmol/l within 4.0±0.3 h after the controlled-release tablets. No significant difference in the fluctuations in individual plasma concentrations during each dose interval at steady state were observed after ordinary capsules compared to controlled-release tablets. The extent of bioavailability was the same. Eight patients reported some side-effects during the capsule period and nine during the controlled-release tablet period.

Notes: Summary Previous studies have suggested that the absorption of L-dopa in the elderly Parkinsonian patient might be unusually efficient. In the present investigation, the systemic availability of L-dopa was examined in 5 elderly Parkinsonian patients (mean age=77 years) and 6 young, healthy volunteers (mean age=26 years) following a single oral 300 mg dose of L-dopa. Quantitation of plasma levels of intact L-dopa was effected by ion-exchange column chromatography and spectrofluorimetry. The L-dopa plasma concentration-time profiles obtained confirmed the considerable intersubject variability in the absorption of L-dopa previously reported in the literature. Maximum plasma concentrations of L-dopa generally occurred within 60 min of administration of the dose. The existence of more than one plasma peak of L-dopa concentration was displayed in 45% of the subjects studied. This characteristic was not confined exclusively to either subject group. There was a significantly larger (P〈0.02) area under the plasma L-dopa concentration-time curve (AUC o ∞ ) in the elderly Parkinsonian patients (mean=234.69 µg · min/ml; SD=84.70) compared to the young, healthy volunteers (mean=82.33 µg · min/ml; SD=31.00). A significant (P〈0.01) correlation existed between AUC o ∞ and age (r=0.7970; n=11) among the subjects studied. The apparent elimination phase plasma half-life of L-dopa in the elderly Parkinsonian patients (mean=66.0 min; SD=11.1) was not significantly different to that observed in the young, healthy volunteers (mean=74.0 min; SD=18.1). These results suggest that there may be an age-related alteration to the disposition of orally administered L-dopa in the elderly Parkinsonian patient.

Notes: Summary The pharmacokinetics of sulpiride was studied in 6 healthy volunteers after intravenous and oral (tablets) administration of 100 mg. An open two- and in two subjects a three-compartment model was applied following intravenous administration. The average total distribution volume during the terminal slope was 2.72±0.66 l/kg and total systemic clearance was 415±84 ml/min. The serum half-life of the terminal slope following intravenous administration averaged 5.3 h (range 3.7–7.1 h) according to the two-compartment model. In two subjects the half-lives were 11.0 and 13.9 h when the three-compartment model was applied. Determination of urinary excretion rates of unchanged sulpiride indicated a half-life of 7.15 h. Following intravenous administration, 70±9% of the dose was recovered unchanged in urine within 36 h; the mean renal clearance was 310±91 ml/min. Sulpiride was absorbed slowly, with peak concentrations appearing between 3 and 6 h after oral administration. The recovery of unchanged drug in urine following oral administration was 15±5% of the dose, with a mean renal clearance of 223±47 ml/min. The bioavailability determined from combined plasma and urine data was only 27±9%. The low bioavailability was probably due to incomplete absorption.

Notes: Summary There is little information about enteral drug absorption during development compared to that about drug distribution, metabolism and excretion. Therefore, the bioavailability, i.e. the amount and rate of absorption of various drugs (sulfonamides, phenobarbital, digoxin, β-methyldigoxin) and test substances (D(+)-xylose, L(+)-arabinose) was investigated in 580 children using pharmacokinetic methods. The amounts of the drugs absorbed, determined by Dost's law of corresponding areas, showed no age dependence. But the rate of absorption, ka, calculated from the concentration time curves using a digital approximation procedure (RIP), is low at the time of birth and reaches adult values after the neonatal period. This phenomenon is identical for all of the substances tested. A prolonged gastric emptying time in the neonate does not seem to be responsible for the delayed absorption since the lagtime is not related to age. Stimulation of intestinal motility with metoclopramide increases the absorption rates, both in neonates and older children, but the age dependent differences remain. Using various dosages of L(+)-arabinose the parameters of the saturation kinetics could be determined. In neonates Vmax values are significantly lower than in older children. Similarly, the affinity constant $$\mathop K\limits^ \star$$ indicates a decreased capacity of enteral absorption in neonates compared with older children. Bioavailability data from adults cannot be accepted without further investigation since the rate of enteral drug absorption depends on age.

Notes: Summary The elimination and bioavailability of two beta-blocking agents, propranolol and sotalol, were studied in 10 thyrotoxic patients, both before and after treatment with iodine-131. Each subject received in random order propranolol 160 mg and sotalol 160mg as single oral doses both while hyperthyroid and after euthyroidism had been achieved. The pharmacokinetics of sotalol was not affected by hyperthyroidism, whereas serum propranolol concentrations were significantly lower during hyperthyroidism than in the euthyroid state. During hyperthyroidism, the bioavailability of propranolol was significantly reduced (p〈0.05) and its clearance was increased (p〈0.005), whereas there was no difference in its serum t1/2. This indicates that the bioavailability of propranolol in hyperthyroidism is reduced by a mechanism which may depend on increased first-pass metabolism in the liver, or on an increased distribution volume of the drug. Both propranolol and sotalol caused a slight decrease in serum tri-iodothyronine concentration. As the effects of beta-blocking agents on the symptoms of hyperthyroidism are correlated with the serum concentration of the drugs, sotalol, with its long half-life and unaltered elimination in hyperthyroidism, has certain advantages over propranolol in the treatment of thyrotoxicosis.

Notes: Summary Two multiple-units controlled-release indomethacin capsule formulations containing enteric-coated pellets were bioequivalent to a standard capsule formulation (taken as the reference) in respect of extent of bioavailability in a crossover study with normal human subjects. However, drug absorption from the enteric-coated pellet formulations was slower, when compared to that from the standard reference capsule. The standard reference capsule released 85% of its drug content in vitro during 10 min at pH 6.5 and 98% during 1 h at pH 7.5. One enteric-coated pellet capsule formulation (I) released 77% during 1 h at pH 6.5 and the other (II) released 10% during 1 h at pH 6.5. Release of drug from each capsule of enteric-coated pellets was complete during 1 h at pH 7.5. Although differences in areas under the plasma indomethacin concentration-time curves were not significantly different, the peak plasma levels and the times of their occurrence indicated that the absorption rates of indomethacin decreased in the order, reference formulation 〉 pellet formulation I 〉 pellet formulation II, which was the same rank order as that of their dissolution rates in vitro. The data indicated that multiple units controlled-release formulations represent a reliable and reproducible source of indomethacin, which by avoiding extremes of local or systemic drug concentrations also should be better tolerated by individuals susceptible to unwanted gastrointestinal and centrally-mediated side-effects.

Notes: Summary Three different pivmecillinam preparations, a conventional 200 mg tablet (P tablet) and two new formulations containing respectively pivmecillinam 200 mg and 400 mg plus Avicel® (microcrystalline cellulose) as a disintegrator (PA tablet), were compared in vitro and in a gastroscopic study in 8 healthy volunteers. Disintegration of the PA tablet was significantly more rapid both in vitro and in the stomach. Following disintegration, the content of the PA tablet was spread over a larger area of the gastric mucosa (1088 mm2) than was observed with the P tablets (408 mm2). Three of the 8 volunteers taking the P tablet developed hyperaemia, interstitial bleeding or erosions of the mucosa of the stomach. No such reactions were seen with the PA tablets. Serum concentrations of mecillinam following ingestion of pivmecillinam tablets were determined in three groups of subjects; fasting volunteers, both supine and ambulant, and in ambulant subjects who took the preparation with a light meal. There was a tendency for the new PA tablets to produce a higher peak serum level as well as greater bioavailability of mecillinam. Administration of the PA tablets with a meal significantly increased the peak serum level and total bioavailability of the drug. On the basis of our observations we recommend adoption of the new PA tablet, because of its quick passage through the oesophagus and its more rapid and complete disintegration in the stomach.

Notes: Summary An high-pressure liquid chromatographic method was used to measure allopurinol and oxipurinol in plasma and urine in 6 healthy volunteers after a single intravenous or oral dose of allopurinol. The influence of coadministrated benzbromarone and hydrochlorothiazide on the pharmacokinetics of allopurinol and oxipurinol was also investigated. After intravenous injection of allopurinol 300 mg the plasma disappearance was biexponential, with a mean distribution half-life of 2.32±1.08 min $$(\bar x \pm SD)$$ and an elimination half-life of 47.8±10.6 min. The total clearance of allopurinol was 11.37±2.70 ml/min/kg, whereas its renal clearance was only 1.73±0.79 ml/min/kg. Oxipurinol disappeared monoexponentially from plasma ith a mean half-life of 12.2±2.6 h. Its renal clearance was 0.42±0.091 ml/min/kg. After oral administration of allopurinol 300 mg the peak plasma concentration of 2.1±0.6 µg/ml (1.5×10−5 M) was reached within 30 to 120 min. The peak level of oxipurinol of 5.8±1.5 µg/ml (3.8×10−5 M) was found within 2 to 5 h after intravenous and oral allopurinol. The bioavailability of oral allopurinol computed from plasma data was 90.4±8.7%. The total recovery from urine was 77% (allopurinol 8%, oxipurinol 69%) after oral and 88% after i.v. administration. It was concluded that about 10% of the oral dose was not absorbed and that 12% was eliminated by an unknown mechanism, presumably as riboside. The pharmacokinetics of allopurinol and oxipurinol were not significantly influenced by coadministration of benzbromarone or hydrochlorothiazide.

Notes: Summary Noscapine was administred to five healthy volunteers in a randomized crossover design, as an intravenous infusion of 66 mg, and as an oral 150 mg dose of either rapidly dissolving tablets or a tablet containing ion exchange resin-bound noscapine. After i.v. administration, the disposition of noscapine was bi-exponential with an elimination half-life of 2.6 h; the total plasma clearance was 22 ml/min/kg and the volume of distribution (Vdarea) was 4.7 l/kg. The absolute oral bioavailability was 30%, with a 3.6-fold interindividual variation. There was no pharmacokinetic evidence to support a prolonged action of the ion exchange resin tablet.

Notes: Summary The pharmacokinetics of bacmecillinam and pivmecillinam were studied in healthy fasting volunteers given tablets in a cross-over, randomized order. The mean (±SD) peak levels of plasma mecillinam were 1.43±0.34, 2.73±0.43, and 4.62±1.41 mg/l after bacmecillinam 100, 200, and 400 mg and 2.38±0.65 mg/l after pivmecillinam 400 mg. The corresponding areas under plasma Vs time curves (AUC) were 2.21±0.19, 3.99±0.63, and 7.74±1.38 mg·h·l−1 for bacmecillinam and 5.35±0.93 mg·h·l−1 for pivmecillinam. The elimination half-lives were 0.8–1.1h for bacmecillinam and 0.7h for pivmecillinam. The 12 h urinary recovery of unchanged mecillinam after the 400 mg doses was 41% for bacmecillinam and 30% for pivmecillinam. The 400 mg dose of bacmecillinam gave a significantly higher plasma peak (p〈0.001), AUC (p〈0.001) and urinary recovery (p〈0.001) than did pivmecillinam 400 mg. The plasma peaks appeared earlier and the rate of absorption was higher after bacmecillinam than after pivmecillinam (p〈0.05). In conclusion, bacmecillinam had a better bioavailability than pivmecillinam in the tablet formulations studied. The AUC increased linearly with increasing doses of bacmecillinam.

Notes: Summary The pharmacokinetics of terodiline HCl was studied in nine healthy volunteers given 12.5 mg i.v. and p.o. or 20 mg i.v. and 25 mg p.o. on two different occasions. The serum concentrations were measured by gas chromatography — mass spectrometry, using deuterated terodiline HCl as the internal standard. After i.v. administration the kinetics could be described by a two-compartment model with a mean distribution half life of 0.3 h and a mean elimination half life of 63 h. The serum clearance and apparent volume of distribution varied about 4-fold with mean values of 4.8 l/h and 417 l, respectively. After oral administration, the mean half life of absorption was 0.7 h and that of elimination 65 h. The absolute bioavailability varied between 64% and 105% with a mean of 92%. The long serum half life of terodiline should permit its once daily administration.

Notes: Summary Differences in the plasma concentrations of drugs after oral administration are caused by two main factors: variation in absorption ratios and in the distribution processes in the body. A new method for the dissection of both types of factors is discussed. The method uses a reference regression of the AUC-values to the corresponding values after intravenous infusion of graded doses. The reference regression is estimated from an appropriate trial. Deviation of the determined AUC-values from the regression curve afford an estimate of the residual variance due to varying distribution volumes or similar random biological effects. For the estimation of absorption ratios after oral administration the drug is given orally to another sample of subjects and their AUC-values are calculated. The deviation of these AUC values due to the above mentioned random effects are simulated using the residual variance of the reference regression, and are subtracted from the observed AUC-values. Then, the differences in the corresponding absorbed doses are transformed by inverting the reference regression. From these doses the empirical distribution function and statistical parameters (e.g. quantiles) are determined. The method has the advantage that no restrictive assumptions are required, such as first order processes, dose linearity, homogeneity of variance or normal distribution of absorption ratios. Its applicability to substances with qualitative differences in their pharmacokinetics is demonstrated by appropriate examples.

Notes: Summary Etilefrine undergoes considerable first-pass metabolism through conjugation in the gut wall. In six volunteers bioavailability was reduced to 35% for a fast release tablet and to 17% for a sustained release preparation. The addition fo dihydroergotamine (DHE) to the sustained release preparation surprisingly increased bioavailability to 61%. The plasma levels of the main metabolite formed during the passage through the gut wall indicated an increase in the rate of enteric absorption and therefore also in bioavailability by DHE. This might be due to the influence of DHE upon the vascular resistance of the vessels in the gut wall or a change in gastro-intestinal motility with a prolongation of drug contact time within the absorbing gut segment.

Notes: Abstract Plasma concentrations of total and unbound sulfisoxazole were followed after single intravenous and oral doses of 1 g sulfisoxazole and during a 500-mg, four-time-a-day dosing regimen in six healthy males, using a specific high pressure liquid Chromatographic assay method. Saturable plasma protein binding was observed at total concentrations above 80–100 mg/liter. The clearance of sulfisoxazole was 18.7±3.9ml/min for total drug and 232±64ml/min for unbound drug. Renal elimination, on the average, accounted for 49% of the clearance of sulfisoxazole. The apparent volume of distribution for total drug was 10.9±2.0 liters and 136±36 liters for unbound drug, indicating that sulfisoxazole is primarily distributed extracellularly. Accumulation of N4-acetyl-sulfisoxazole during multiple dosing did not affect the disposition of sulfisoxazole. Adjusting for variable renal clearances between oral and intravenous administration and using the unbound plasma concentrations, the bioavailability for an oral dose of sulfisoxazole was found to be 0.95±0.04.

Notes: Abstract The bioavailability of phenytoin from rapid release capsule and oral solution formulations relative to that of a slow release capsule formulation was assessed in five patients who had participated in a three-way crossover study performed at steady state. The subjects then underwent dosage adjustment utilizing the slow release formulation, and estimates of their Michaelis-Menten parameters thus obtained were utilized in calculating the relative bioavailabilities. In addition, expected changes in steady-state plasma phenytoin concentrations were calculated assuming initial levels of 15 mg/liter, with increases and decreases in bioavailability of 10%. The consequences of such alterations in the extent of phenytoin absorption or average content of the dosage form may be clinically significant, particularly where the initial phenytoin level is equal to or greater than the patient's operative Km.

Notes: Abstract Current information on the pharmacokinetics of disopyramide is reviewed with emphasis on the implications for antiarrhythmic therapy. The absolute bioavailability, the disposition half-life, the plasma clearance, and the renal clearance for normal subjects and patients are discussed. Drug-drug interactions are discussed, and a new flexible intravenous dosing schedule is proposed.

Notes: Abstract The literature growth in pharmacokinetics and bioavailability between the years 1964 and 1980 is analyzed. During much of this period, the literature doubled approximately every 1.6 years. However, during the period 1978–1980, little or no growth was observed. During the period 1950–1967, the total chemical literature increased exponentially with a half-life of 8.28 years; between 1968 and 1980, the half-life was 12.4 years. Thus, the pharmacokinetic literature increased at a much more rapid pace than did the total chemical literature in general. The subject of growth is considered in a general context, particularly as influenced by psychological, sociological, political, and economic factors. It is concluded that while mathematical functions may adequately describe past literature trends, they have little if any utility in predicting future trends in specific research areas such as pharmacokinetics.

Notes: Abstract The pharmacokinetics of chloramphenicol (CAP) and total chloramphenicol succinate (CAPS) were studied in eight hospitalized adult patients with normal renal and hepatic function receiving intravenous chloramphenicol sodium succinate therapy. The steady-state peak concentrations of CAP (8.4–26.0 μg/ml) occurred at an average of 18.0 min (range 5.4–40.2) after cessation of the chloramphenicol sodium succinate infusion. Unhydrolyzed CAPS prodrug, representing 26.0±7.0% of the dose, was recovered unchanged in the urine indicating that the bioavailability of CAP from a dose of intravenous chloramphenicol succinate is not complete. A pharmacokinetic model was developed for simultaneous fitting of CAP and CAPS plasma concentration data. Pharmacokinetic parameters determined by simultaneous fitting were: V, 0.81±0.18 liters/kg; t1/2, 3.20 ±1.02 hr; CLB, 3.21±1.27 ml/min/kg for chloramphenicol; and V, 0.38±0.13 liters/kg; t1/2, 0.57±0.12hr; CLB, 7.72±1.87 ml/min/kg for total chloramphenicol succinate.

Notes: Abstract The pharmacokinetics and bioavailability of nitrazepam following intravenous, oral (tablet), and rectal (solution) administration were studied in seven healthy, young male volunteers. Nitrazepam plasma concentrations were determined by electron-capture GLC; pharmacokinetic evaluations were made by compartmental analysis (NONLIN) and compared with the results obtained by a less stringent modelling of the data. The plasma concentration-time profile was similar for all three routes of administration. Mean kinetic parameters as obtained by compartmental analysis of i.v. nitrazepam were: distribution half-life 17 min; volume of distribution after equilibrium 2.14 liters/kg; total plasma clearance 61.6 ml/min; elimination half-life 29.0 h. The mean protein unbound fraction of nitrazepam in plasma was 12.3% and the clearance of the unbound fraction was 506 ml/min. Absorption of oral nitrazepam started after the elapse of a lag time (mean value 12 min) and occurred as an apparent first-order process in all but one subject, with a mean absorption half-life of 16 min. Distribution and elimination half-lives were comparable with those following i.v. administration. Following rectal administration of the nitrazepam solution, rapid first-order absorption occurred with a mean lag time of 4 min and a mean absorption half-life of 9 min. Peak times (median 18 min) were significantly shorter than following oral administration (median 38 min), but there was little difference in peak concentrations. The distribution half-life was similar to i.v. and oral administration, but the elimination half-lives were longer with a mean value of 33.1 h. Following i.v. administration a good agreement was found between the results obtained by compartmental analysis using NONLIN and those obtained by a less stringent modelling of the data. Following oral and rectal administration, a good agreement between the two procedures was found for the elimination half-life; estimation of bioavailability, however, was higher by compartmental analysis. The mean bioavailability data showed that absorption is complete when nitrazepam is given orally and almost 20% lower when it is given rectally, but considerable interindividual differences were observed.

Notes: Abstract The procedure of deconvolution to evaluate the rate and the extent of input from absorption data and data from intravenous administration is the most fundamental and least assumptive method of accurately evaluating drug absorption in linear pharmacokinetics. It is shown for linear systems that if the absorption response and the response from an intravenous infusion or bolus administration are both well approximated by a polyexponential function, then the rate of absorption can be expressed as a sum of exponentials. An algorithm and computer program are presented whereby the absorption function is uniquely defined from the model-independent parameters of the polyexponential expressions fitted to the absorption data and data from intravenous administration. Fitting a sum of exponentials to data has become a routine procedure in pharmacokinetics. The method presented therefore makes the previously complex task of deconvolution a simple procedure. The deconvolution approach is discussed in relation to conventional methods of evaluating drug absorption and appears to have some distinct advantages over these methods. The method is tested using simulated data and demonstrated using pentobarbital and cimetidine data from human subjects.

Notes: Abstract The gastrointestinal absorption of quinidine from three commercially available tablet products has been compared to that from a quinidine sulfate solution previously found to have 70% of the systematic availability of an intravenous dose. Quinidine gluconate solution was included in the study to compare the absorption characteristics of the two quinidine salts. The tablets were given in a counterbalanced sequence preceded by one quinidine solution and followed by the other in a crossover design. The three tablets proved to be equivalent to one another with respect to extent and rate of absorption. The absorption properties of the two solutions were indistinguishable. The tablets were equivalent to the solutions in extent but not in rate of absorption.

Notes: Abstract In a single-dose bioavailability study, Wales, Robinson, Columbia, and Choledyl (Warner/Chilcott) enteric-coated tablets all allowed a bioavailability of theophylline (99%±25%, 102%±23%,103%±18%, and 98%±15%;mean±SD, n=12) statistically indistinguishable from that of the standard uncoated tablet (Searle 200 mg aminophylline). Only the Wales and Choledyl tablets (7.6, 4.2 hr) could be shown (p〈0.05) to generate a peak plasma theophylline concentration later than the standard (1.4 hr). All tablet brands demonstrated a significant lag time before appearance of theophylline in the plasma, and both Wales and Choledyl tablets also had a (t peak -t tag )statistically different from that of the standard. Despite misleading indications from the mean plasma profile (plasma concentrations at each sampling time averaged over all subjects), plasma data from the individual participants and in vitrodissolution data show that, while release of theophylline from the Wales tablet might be inordinately slow, this is not a sustained-release preparation. Of the enteric-coated tablets only the Columbia product allowed significant levels in the first sample after dosage. Five of the 18 Columbia doses gave rise to 40–99%of the peak concentration in the 1- hr sample. In vitro,it takes 39±14 min for 40% of the theophylline content of Columbia tablets to dissolve in simulated intestinal fluid. Surprisingly rapid delivery of an entericcoated tablet to the duodenum would appear to be required to allow a significant percentage of theophylline to be dissolved and absorbed before 1 hr. None of 12 Columbia tablets tested in vitro,however, allowed dissolution of more than 0.2% of their theophylline content during 1 hr immersion in simulated gastric fluid. Since once in intestinal fluid Columbia tablets appear to dissolve more rapidly than the other enteric products, it is not clear whether the five Columbia tablets in question had imperfections or whether, in fact, this tablet brand more closely than the others represents the ideal of immediate release once in the duodenum. Plasma samples should be taken as early as 15 min after dosage when evaluating the bioavailability of enteric release products.

Notes: Abstract The relative bioavailability of ten marketed dosage forms of griseofulvin was evaluated in two separate crossover studies. Each study utilized 12 healthy subjects, with eight of the subjects being common to both studies. Plasma griseofulvin concentrations were determined 1, 2, 3, 4, 6, 8, 10, 25, 34, 49, and 73 hr after dosing, using a high-pressure liquid chromatographic method. The “high-dose” study compared four microsize dosage forms administered as 500-mg doses and two ultramicrosize formulations given as 250-mg doses. The “low-dose” study employed four 250-mg microsize products and two 125-mg ultramicrosize products. The individual plasma level-time profiles for the majority of doses suggested prolonged absorption of microsize griseofulvin. The ultramicrosize dosage forms exhibited peak concentrations which were not significantly different (p〉0.05) from those of the microsize products administered as twice the dose. In the high-dose study, the two 250-mg ultramicrosize dosage forms exhibited areas under the plasma level-time curve (AUC) which were significantly (p〈0.05) less than the AUCs for all but one of the 500-mg microsize products. In the low-dose study the AUCs for the ultramicrosize products were significantly lower than the AUCs for all of the microsize dosage forms. Significant differences were also noted among the AUCs for the microsize products, although the maximum difference was less than 20% in both studies. A comparison of the AUCs observed in the high- and low-dose studies revealed that the AUCs for two of the 500-mg microsize dosage forms were only approximately 75% the AUC predicted from the 250-mg dose for the eight subjects common to both studies. All other formulations exhibited a dose proportionality for AUC.

Notes: Abstract Absorption of theophylline from three commercial products labeled as sustained release was compared to the absorption from a standard uncoated tablet (Searle 200-mg aminophylline tablet) in a single-dose study. Aminodur tablets (Cooper) and Slophyllin Gyrocap capsules (Dooner) had bioavailability (100.2%±19.8% and 98.5%±13.8%) statistically indistinguishable from that of the standard but showed significantly slower absorption (peak times of 10,4±2.8 and 4.36±1.35 hr) and lower peak plasma concentrations (13.9±4.5 and 22.6±3.5gmg/ml/g dose) than the standard (t peak ,1.52±0.45 hr; Cpeak,28.l±6.2μg/ml/g dose). The time of the plasma concentration peak (2.47±1.38 hr) after a dose of Tedral S.A. (Warner/Chilcott) was not statistically different from that after the standard, but both the peak concentration (16.0±3.9 gmg/ml/g dose) and bioavailability (76.0±18.4%) were. Multiple-dose projections from single-dose data indicate that of the three test products only Aminodur maintains reasonably constant interdose plasma levels during 12 hourly dosing. With an 8 hourly dosing schedule Gyrocaps also might be satisfactory. Reasonable predictions of the plasma concentrations arising from Aminodur doses have been made using a single-compartment body model and assuming input from an outer followed by an inner layer of the tablet. Typically a single dose of a preparation designed for constant release of drug over 12 hr should not produce a plasma concentration plateau in subjects with an average 6.1-hr drug half-life. The apparent plateau in the mean plasma profile (i.e., concentrations at each sampling time averaged over all subjects) for Aminodur doses is evaluated. The interpretation commonly being implied in the publication of mean profiles from bioavailability studies is misleading, particularly when applied to sustained-release preparations.

Notes: Abstract Seasonal and regional variations in the speciation, sediment-water partitioning, and dynamics of mercury (Hg) were studied at selected sites along the Hg-polluted Wabigoon River, and at unpolluted headwater and tributary sites, during April–September, 1979. ‘Dissolved’ and ‘particulate’ forms of Hg in the water were separated by continuous-flow centrifugation in the field. The Hg and other pollutants such as wood chips and salt had been discharged from a chlor-alkali plant and paper mill at Dryden, Ontario. Concentrations and loadings of particulate methyl mercury (CH3Hg+) and total particulate Hg (and loadings of total ‘dissolved’ Hg) were greatest during the spring flood (April-May) owing to accelerated resuspension and transport of sediments. Concentrations of ‘dissolved’ CH3Hg+, however, were highest in the summer (July–September), probably reflecting stimulation of microbial methylating activity by elevated temperatures, together with factors such as reduced levels of metal-scavenging particulates and minimal dilution by runoff. Total dissolved Hg concentrations were relatively high in September at polluted sites only, possibly because of desorption from sediments due to elevated concentrations of Cl− ions. Loadings of dissolved CH3Hg+ tended to be high in the summer but were generally depressed (suggesting sorption by suspended particles) during the major spring-flood episode in May. During July–August dissolved CH3Hg+ was a function of total dissolved Hg, suggesting rapid biomethylation of desorbed inorganic Hg; but in general dissolved and suspended CH3Hg+ levels depended on environmental variables and were unrelated to total Hg concentrations. In the summer only, total dissolved Hg was a function of dissolved Cl−. Hg species in particulates were associated with sulfides, hydrated Fe and Mn oxides, organic matter (notably high molecular weight humic and humic-Fe components), and selenium (Se); but CH3Hg+ and total Hg differed in their specific preferences for binding agents, implying that binding sites discriminate between CH3Hg+ and Hg2+ ions. CH3Hg+ was associated with sulfide and (in the spring only) with Fe oxides, whereas total Hg was associated with organic matter and Se and with DTPA- and NaOH-extractable Fe in the spring but with Mn oxide and NaOH-extractable organics in the summer. Sulfides were most abundant in May, indicating that they were eroded from bottom sediments, but Fe and Mn oxides were most abundant in the summer, probably owing to activities of filamentous iron bacteria and other micro-organisms. Particulate Hg was 98–100% nonextractable by mild solvents such as Ca acetate, CaCl2, dilute acetic acid, and (at polluted sites only) DTPA solutions, suggesting that the particulate Hg mobilized in the spring may not be readily available to organisms; association with Se and high molecular weight humic matter also supports this hypothesis. Hg probably becomes more bio-available in the summer, as suggested by the upsurge in dissolved CH3Hg+ and total dissolved Hg levels, and by increases in the solubility of particulate Hg in acetic acid, DTPA, H2O2, and NaOH solutions, as well as an increase in the relative importance of lower molecular weight fractions of NaOH-extractable Hg (in September). Regional variations in Hg speciation and partitioning reflected a gradient in sediment composition from wood chips near Dryden to silt-clay mud further downstream. Hg in silt-clay mud relatively far (〉 35 km) downstream from the source of pollution or in unpolluted areas appeared to be more readily solubilized by Cl− ions or chelators such as DTPA, more readily methylated (as indicated by downstream increases in dissolved CH3Hg+ levels and CH3Hg+/total Hg ratios), and was to a greater degree organically bound (H2O2-extractable), and thus was probably more bio-available, than Hg in wood-chip deposits. Possible explanations include weaker binding of Hg by the mud, the more finely divided state of the mud, and improved microbial growth at lower concentrations of toxic pollutants. Owing to enrichment in sulfides and Fe oxides, resuspended wood-chip sediments were especially efficient scavengers of CH3Hg+. The results indicate that in any pollution abatement plan aimed at lowering the Hg levels in the biota of lakes fed by the Wabigoon River, immobilization, removal, or detoxification of dissolved as well as particulate forms of Hg in the river would probably have to be considered. Possibly, Hg species could be ‘scrubbed’ from the river water by increasing the suspended load and by sedimentation and treatment with Hg-binding agents in special receiving basins.

Notes: Abstract Seasonal and regional variations in the speciation, sediment-water partitioning, and dynamics of mercury (Hg) were studied at selected sites along the Hg-polluted Wabigoon River, and at unpolluted headwater and tributary sites, during April–September, 1979. ‘Dissolved’ and ‘particulate’ forms of Hg in the water were separated by continuous-flow centrifugation in the field. The Hg and other pollutants such as wood chips and salt had been discharged from a chlor-alkali plant and paper mill at Dryden, Ontario. Concentrations and loadings of particulate methyl mercury (CH3Hg+) and total particulate Hg (and loadings of total ‘dissolved’ Hg) were greatest during the spring flood (April-May) owing to accelerated resuspension and transport of sediments. Concentrations of ‘dissolved’ CH3Hg+, however, were highest in the summer (July–September), probably reflecting stimulation of microbial methylating activity by elevated temperatures, together with factors such as reduced levels of metal-scavenging particulates and minimal dilution by runoff. Total dissolved Hg concentrations were relatively high in September at polluted sites only, possibly because of desorption from sediments due to elevated concentrations of Cl− ions. Loadings of dissolved CH3Hg+ tended to be high in the summer but were generally depressed (suggesting sorption by suspended particles) during the major spring-flood episode in May. During July–August dissolved CH3Hg+ was a function of total dissolved Hg, suggesting rapid biomethylation of desorbed inorganic Hg; but in general dissolved and suspended CH3Hg+ levels depended on environmental variables and were unrelated to total Hg concentrations. In the summer only, total dissolved Hg was a function of dissolved Cl−. Hg species in particulates were associated with sulfides, hydrated Fe and Mn oxides, organic matter (notably high molecular weight humic and humic-Fe components), and selenium (Se); but CH3Hg+ and total Hg differed in their specific preferences for binding agents, implying that binding sites discriminate between CH3Hg+ and Hg2+ ions. CH3Hg+ was associated with sulfide and (in the spring only) with Fe oxides, whereas total Hg was associated with organic matter and Se and with DTPA- and NaOH-extractable Fe in the spring but with Mn oxide and NaOH-extractable organics in the summer. Sulfides were most abundant in May, indicating that they were eroded from bottom sediments, but Fe and Mn oxides were most abundant in the summer, probably owing to activities of filamentous iron bacteria and other micro-organisms. Particulate Hg was 98–100% nonextractable by mild solvents such as Ca acetate, CaCl2, dilute acetic acid, and (at polluted sites only) DTPA solutions, suggesting that the particulate Hg mobilized in the spring may not be readily available to organisms; association with Se and high molecular weight humic matter also supports this hypothesis. Hg probably becomes more bio-available in the summer, as suggested by the upsurge in dissolved CH3Hg+ and total dissolved Hg levels, and by increases in the solubility of particulate Hg in acetic acid, DTPA, H2O2, and NaOH solutions, as well as an increase in the relative importance of lower molecular weight fractions of NaOH-extractable Hg (in September). Regional variations in Hg speciation and partitioning reflected a gradient in sediment composition from wood chips near Dryden to silt-clay mud further downstream. Hg in silt-clay mud relatively far (〉 35 km) downstream from the source of pollution or in unpolluted areas appeared to be more readily solubilized by Cl− ions or chelators such as DTPA, more readily methylated (as indicated by downstream increases in dissolved CH3Hg+ levels and CH3Hg+/total Hg ratios), and was to a greater degree organically bound (H2O2-extractable), and thus was probably more bio-available, than Hg in wood-chip deposits. Possible explanations include weaker binding of Hg by the mud, the more finely divided state of the mud, and improved microbial growth at lower concentrations of toxic pollutants. Owing to enrichment in sulfides and Fe oxides, resuspended wood-chip sediments were especially efficient scavengers of CH3Hg+. The results indicate that in any pollution abatement plan aimed at lowering the Hg levels in the biota of lakes fed by the Wabigoon River, immobilization, removal, or detoxification of dissolved as well as particulate forms of Hg in the river would probably have to be considered. Possibly, Hg species could be ‘scrubbed’ from the river water by increasing the suspended load and by sedimentation and treatment with Hg-binding agents in special receiving basins.

Notes: Abstract Control of phytoplankton production in the Great Lakes can be achieved most efficiently by limiting inputs of biologically available P. We report the results of studies performed to characterize the chemical forms and availability of particulate P in wastewater and tributaries which enter the lower Lakes, the eroding bluffs which border Lake Erie, and bottom samples from the near-shore of western Lake Erie. Rates of release of available P were estimated from a simple first-order model of the process, as observed during algal bioassays. Available P in wastewater samples, as a fraction of total particulate P, was affected minimally by wastewater treatment, including chemical precipitation and filtration; it correlated well with levels of total particulate P. Available particulate P levels in fluvial suspended sediments showed regional uniformity, but appeared to be strongly dependent on levels of both NaOH-P and CDB-P. Rates of release of available P decreased during wastewater treatment to values which were similar in magnitude to those observed for fluvial sediments. Release rates, however, were not related to any of the particulate P fractions which were measured. Analysis of the bluff and bottom samples indicated that P availability in the former was negligible, but the latter contained levels which approached those of wastewater particulates, though available P was released from the bottom sediments at relatively low rates.

Notes: Abstract Control of phytoplankton production in the Great Lakes can be achieved most efficiently by limiting inputs of biologically available P. We report the results of studies performed to characterize the chemical forms and availability of particulate P in wastewater and tributaries which enter the lower Lakes, the eroding bluffs which border Lake Erie, and bottom samples from the near-shore of western Lake Erie. Rates of release of available P were estimated from a simple first-order model of the process, as observed during algal bioassays. Available P in wastewater samples, as a fraction of total particulate P, was affected minimally by wastewater treatment, including chemical precipitation and filtration; it correlated well with levels of total particulate P. Available particulate P levels in fluvial suspended sediments showed regional uniformity, but appeared to be strongly dependent on levels of both NaOH-P and CDB-P. Rates of release of available P decreased during wastewater treatment to values which were similar in magnitude to those observed for fluvial sediments. Release rates, however, were not related to any of the particulate P fractions which were measured. Analysis of the bluff and bottom samples indicated that P availability in the former was negligible, but the latter contained levels which approached those of wastewater particulates, though available P was released from the bottom sediments at relatively low rates.

Notes: Abstract Seasonal and regional variations in the speciation, sediment-water partitioning, and dynamics of mercury (Hg) were studied at selected sites along the Hg-polluted Wabigoon River, and at unpolluted headwater and tributary sites, during April–September, 1979. ‘Dissolved’ and ‘particulate’ forms of Hg in the water were separated by continuous-flow centrifugation in the field. The Hg and other pollutants such as wood chips and salt had been discharged from a chlor-alkali plant and paper mill at Dryden, Ontario. Concentrations and loadings of particulate methyl mercury (CH3Hg+) and total particulate Hg (and loadings of total ‘dissolved’ Hg) were greatest during the spring flood (April-May) owing to accelerated resuspension and transport of sediments. Concentrations of ‘dissolved’ CH3Hg+, however, were highest in the summer (July–September), probably reflecting stimulation of microbial methylating activity by elevated temperatures, together with factors such as reduced levels of metal-scavenging particulates and minimal dilution by runoff. Total dissolved Hg concentrations were relatively high in September at polluted sites only, possibly because of desorption from sediments due to elevated concentrations of Cl− ions. Loadings of dissolved CH3Hg+ tended to be high in the summer but were generally depressed (suggesting sorption by suspended particles) during the major spring-flood episode in May. During July–August dissolved CH3Hg+ was a function of total dissolved Hg, suggesting rapid biomethylation of desorbed inorganic Hg; but in general dissolved and suspended CH3Hg+ levels depended on environmental variables and were unrelated to total Hg concentrations. In the summer only, total dissolved Hg was a function of dissolved Cl−. Hg species in particulates were associated with sulfides, hydrated Fe and Mn oxides, organic matter (notably high molecular weight humic and humic-Fe components), and selenium (Se); but CH3Hg+ and total Hg differed in their specific preferences for binding agents, implying that binding sites discriminate between CH3Hg+ and Hg2+ ions. CH3Hg+ was associated with sulfide and (in the spring only) with Fe oxides, whereas total Hg was associated with organic matter and Se and with DTPA- and NaOH-extractable Fe in the spring but with Mn oxide and NaOH-extractable organics in the summer. Sulfides were most abundant in May, indicating that they were eroded from bottom sediments, but Fe and Mn oxides were most abundant in the summer, probably owing to activities of filamentous iron bacteria and other micro-organisms. Particulate Hg was 98–100% nonextractable by mild solvents such as Ca acetate, CaCl2, dilute acetic acid, and (at polluted sites only) DTPA solutions, suggesting that the particulate Hg mobilized in the spring may not be readily available to organisms; association with Se and high molecular weight humic matter also supports this hypothesis. Hg probably becomes more bio-available in the summer, as suggested by the upsurge in dissolved CH3Hg+ and total dissolved Hg levels, and by increases in the solubility of particulate Hg in acetic acid, DTPA, H2O2, and NaOH solutions, as well as an increase in the relative importance of lower molecular weight fractions of NaOH-extractable Hg (in September). Regional variations in Hg speciation and partitioning reflected a gradient in sediment composition from wood chips near Dryden to silt-clay mud further downstream. Hg in silt-clay mud relatively far (〉 35 km) downstream from the source of pollution or in unpolluted areas appeared to be more readily solubilized by Cl− ions or chelators such as DTPA, more readily methylated (as indicated by downstream increases in dissolved CH3Hg+ levels and CH3Hg+/total Hg ratios), and was to a greater degree organically bound (H2O2-extractable), and thus was probably more bio-available, than Hg in wood-chip deposits. Possible explanations include weaker binding of Hg by the mud, the more finely divided state of the mud, and improved microbial growth at lower concentrations of toxic pollutants. Owing to enrichment in sulfides and Fe oxides, resuspended wood-chip sediments were especially efficient scavengers of CH3Hg+. The results indicate that in any pollution abatement plan aimed at lowering the Hg levels in the biota of lakes fed by the Wabigoon River, immobilization, removal, or detoxification of dissolved as well as particulate forms of Hg in the river would probably have to be considered. Possibly, Hg species could be ‘scrubbed’ from the river water by increasing the suspended load and by sedimentation and treatment with Hg-binding agents in special receiving basins.