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  • pharmacokinetics  (84)
  • Springer  (84)
  • 1980-1984  (84)
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  • Springer  (84)
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  • 1
    ISSN: 1432-1041
    Keywords: zimelidine ; norzimelidine ; antidepressants ; pharmacokinetics ; bioavailability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    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.
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  • 2
    ISSN: 1432-1041
    Keywords: chlordiazepoxide ; alcoholic liver disease ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The clearance of chlordiazepoxide from the systemic circulation was studied in 20 subjects which included 15 patients with alcoholic hepatitis and 5 normal volunteers. The half-life for the appearance of the drug in the systemic circulation was found to increase exponentially with age (r=0.73, P〈0.0005) and was independent of the presence of alcoholic hepatitis. The metabolic clearance of chlordiazepoxide was significantly lower in the patients than in the normal subjects (7.6 compared to 13.8 ml/kg-h, P〈0.005). Linear regression analysis revealed a significant correlation between clearance and albumin (r=0.77, P〈0.00005). However, the predictive value of this relationship was shown to be minimal. Multiple regression analysis produced only a slight improvement in the correlation when both albumin and lactate dehydrogenase were used as variables (r=0.83, P〈0.00005). In six of the patients, a second clearance study was conducted three weeks following their initial one. All repeat subjects showed improvement both clinically and as reflected by their laboratory tests for liver injury, but there was not a significant change in their clearance of chlordiazepoxide. Multiple regression analysis of the clearance data on the initial and repeat subjects showed a significant correlation between clearance and the variables age, albumin, and lactate dehydrogenase (r=0.91, P〈0.0025). This relationship suggests that over a short period of time (where age can be considered constant) changes in albumin and lactate dehydrogenase could be potentially useful in predicting clearance changes in a single individual.
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  • 3
    ISSN: 1432-1041
    Keywords: cimetidine ; intravenous infusion ; pharmacokinetics ; peptic ulcer ; duration of infusion ; acute dose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The use of cimetidine administered by bolus intravenous injection to critically ill patients has been associated with serious cardiac arrhythmias, due presumably to high initial plasma concentrations. The aim of this study was to determine the range of infusion times of a single 200 mg dose of cimetidine which would avoid high initial drug concentrations while maintaining a duration of effective concentrations no less than that resulting from bolus injection. Computer simulations of both maximum plasma cimetidine concentrations and duration of effective plasma cimetidine concentrations versus duration of infusion were based on mean pharmacokinetic date from 6 peptic ulcer patients who had received cimetidine 200 mg i.v. over 5 min. The simulations indicated that to reduce maximum plasma cimetidine concentrations by at least 50%, while maintaining the duration of effective plasma concentrations, the infusion time should be at least 30 min and no longer than 4.5 h. The validity of the simulations was subsequently tested in 4 of the patients, who received cimetidine 200 mg i.v. over 30 min. The mean maximum plasma concentration for the 30 min infusion (4.57±0.53 µg/ml) was, as predicted, approximately half that corresponding to bolus administration in these patients (8.97±1.96 µg/ml). Moreover, the duration of effective concentrations for the infusion (1.43±0.28 h) was significantly greater than that for the 5 min infusion (1.21±0.31 h). We suggest that where an acute intravenous dose of cimetidine (200 mg) is indicated, it should be administered over at least 30 min rather than as a bolus.
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  • 4
    ISSN: 1432-1041
    Keywords: neuromuscular relaxants ; fazadinium ; pharmacokinetics ; renal failure ; neuromuscular transmission
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The pharmacokinetic behaviour and neuromuscular blockade produced by the administration of fazadinium bromide at a dose of 1 mg/kg have been studied in seven patients with end-stage renal failure. No significant differences were found in the pharmacokinetic or pharmacodynamic properties when compared with patients with normal renal function. It is suggested that fazadinium may be superior to either d-tubocurarine or pancuronium in providing muscle relaxation for patients with renal failure.
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  • 5
    ISSN: 1432-1041
    Keywords: astemizole ; ethanol ; antihistamine ; pharmacodynamics ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The effects of astemizole (10 mg daily for 7 days) on the kinetics and CNS depressant activity of ethanol have been examined in a double-blind cross-over study agonist placebo in 7 volunteers. There was no significant change in the elimination rate or AUC of the plasma ethanol concentration-time curve after astemizole. Central nervous system effects of ethanol as monitored by visual analogues of sedation, visual discrimination, pursuit rotor and reaction time were also unaffected by astemizole pretreatment.
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  • 6
    ISSN: 1432-1041
    Keywords: furosemide ; triamterene ; drug combination ; pharmacodynamics ; pharmacokinetics ; furosemide retard ; triamterene metabolite ; urine potassium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The pharmacodynamics and pharmacokinetics of the combination of furosemide retard (30 mg)/triamterene (50 mg) were compared with furosemide (30 mg) in 18 healthy male volunteers aged 39.3±6.3 years. After the administration of furosemide the onset of its effect was very rapid, reaching a maximum between 1.5 to 3 h, and followed by rebound after 9 to 10.5 h. In contrast the combination furosemide retard/triamterene showed a protracted course with a duration of effect up to 12 h. The general effect over 12 h of the two preparations was equivalent with respect to the excretion of urine, sodium, chloride and calcium, but the combination caused significantly less excretion of potassium (p≤0.05) than furosemide. After a lag-phase of 33.9±5.4 min the maximum plasma concentration of furosemide was reached after 3.47±0.66 h, and the elimination half-life was approximately 2 h. After a lag-phase of 33.0±17.8 min the maximum plasma concentration of the main metabolite of triamterene, the OH-TA sulphuric acid ester, was reached after 1.7±0.59 h, and its elimination half-life amounted to 1.25±0.37 h. Because of the sustained release of furosemide from the retard-formulation, its principal pharmacokinetic parameters were better adapted to those of triamterene. The consequences were not only a protracted effect but also an improved electrolyte profile, especially with regard to reduced loss of potassium. In the case of renal insufficiency, however, the potassium level in serum might be increased to an undesirable extent.
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  • 7
    ISSN: 1432-1041
    Keywords: tobramycin ; newborn infants ; intrapatient variations ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary Nineteen newborn infants receiving tobramycin, 2.5 mg/kg every 12 h were studied on two occasions at steady-state during the first week of postnatal age. The two studies were separated by two to four days. Total body clearance of tobramycin averaged 1.15 and 1.14 ml/min/kg (p〉0.05), apparent volume of distribution averaged 0.82 and 0.68 l/kg (p〉0.05), and elimination half-life averaged 8.6 and 7.1 h (p〉0.05), during the first and second study, respectively. When the data were further analyzed based on the birth weight, tobramycin kinetics changed during the second study compared to the first study in very low birth weight infants. In eight infants ⩽1.5 kg birth weight, although total clearance of tobramycin was similar, the average apparent volume of distribution decreased from 1.04 l/kg during the first study to 0.73 l/kg during the second study (p〈0.05) and elimination half-life from 11.1 h during the first study to 8.7 h during the second study (p〈0.05). These data indicate that these infants may require a change in dosing interval with continued tobramycin therapy during the first week of postnatal age. Intrapatient variation in tobramycin kinetics should be considered, in addition to the interpatient variation reported previously, when monitoring the serum concentration to individualize tobramycin therapy in newborn infants ⩽1.5 kg birth weight.
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  • 8
    ISSN: 1432-1041
    Keywords: acetaminophen ; pediatric patients ; fever therapy ; accumulation ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary Acetaminophen serum concentrations were studied in 21 infants and children with fever. The maximum serum concentrations ranged from 9.96 to 19.6 µg/ml after a single dose of 12–14 mg/kg and 13.9 to 40.1 µg/ml after a single dose of 22–27 mg/kg. Ten patients were restudied at steadystate after repeat doses had been given every 4 or 8 h for 1 to 3 days. Total area under the acetaminophen serum concentration-time curve normalized for dose averaged 0.181 (ml/min/kg)−1 after the first dose and 0.202 (ml/min/kg)−1 at steady-state (p〈0.05). Five patients showed a 13 to 44% increase in the AUC; one had a 10% decrease in the AUC; and four had less than 6% change in the AUC. There was no evidence of hepatotoxicity. These data suggest that acetaminophen may accumulate after repeated therapeutic doses in children with fever.
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  • 9
    ISSN: 1432-1041
    Keywords: tolmesoxide ; metabolite ; volunteers ; pharmacokinetics ; intravenous ; oral ; protein binding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary A high pressure liquid chromatographic assay was developed for simultaneous measurement of the plasma levels of tolmesoxide and its principal metabolite, RX71112. The assay was used to study the disposition of intravenous and oral tolmesoxide in ten normotensive subjects. Two exponential terms were required to describe the disposition of the drug following intravenous administration, whilst a single exponential term sufficied to account for the decay in the plasma concentration after oral administration. The bioavailability of oral tolmesoxide from capsules averaged 84.5% and was independent of dose. The mean half-life after i. v. dosing was 2.6 h (±0.3 SEM) compared to values of 1.9 h (±0.1 SEM) and 2.7 h (±0.5 SEM) following 200 and 400 mg oral doses respectively. In all subjects RX71112 appeared in plasma shortly after tolmesoxide following both routes of administration. The terminal half-life of the metabolite was significantly longer than tolmesoxide with a mean value of 4.9 h (±0.9 SEM) following the 200 mg oral dose of tolmesoxide. The binding of tolmesoxide and RX71112 at therapeutic plasma concentration was 36.8% (±0.5 SEM) and 58.5% (±0.3 SEM) and this remained unchanged at higher concentrations.
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  • 10
    ISSN: 1432-1041
    Keywords: diclofenac sodium ; rheumatoid disease ; healthy subjects ; serum albumin ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary Pharmacokinetic data for diclofenac sodium has been well established in healthy volunteers, whereas in patients with rheumatoid arthritis very little information is available in the literature. A single oral dose of enteric-coated diclofenac sodium was given to 10 patients with active rheumatoid disease, adopting the same procedures used for a group of 10 healthy volunteers in whom pharmacokinetic data was already available. Plasma specimens were collected over a period of 8h following administration and concentrations of diclofenac determined by GLC. Resulting plasma concentration curves were similar to those obtained in the healthy subjects in that areas under curves and terminal half-lives were comparable. However, peak concentrations of diclofenac were significantly reduced in the rheumatoid patients. The lower peak concentrations were correlated with the lower serum albumin levels in the patients which are associated with active rheumatoid disease.
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