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  • 1
    Electronic Resource
    Electronic Resource
    Upper Gastrointestinal pH in Seventy-Nine Healthy, Elderly, North American Men and Women (1993)
    Springer
    Pharmaceutical research 10 (1993), S. 187-196 
    Details
    ISSN: 1573-904X
    Keywords: gastric pH ; duodenal pH ; elderly ; gender effects ; food effects ; fasted-state pH ; fed-state pH ; Heidelberg radiotelemetry capsule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Gastric and duodenal pH levels were measured in 79 healthy, elderly men and women (mean ± SD = 71 ± 5 years) under both fasted and fed conditions using the Heidelberg capsule technique. The pH was recorded for 1 hr in the fasted state, a standard liquid and solid meal of 1000 cal was given over 30 min, then the pH was measured for 4 hr postprandially. Results are given as medians and interquartile ranges: fasted gastric pH, 1.3 (1.1–1.6); gastric pH during the meal, 4.9 (3.9–5.5); fasted duodenal pH, 6.5 (6.2–6.7); and duodenal pH during the meal, 6.5 (6.4–6.7). Although fasted gastric pH, fasted duodenal pH, and duodenal pH during the meal differ statistically from those observed in young subjects, the differences are not expected to be clinically significant in terms of drug absorption for the majority of elderly subjects. Following a meal, gastric pH decreased from a peak pH of 6.2 (5.8–6.7) to pH 2.0 within 4 hr in most subjects. This rate of return was considerably slower than in young, healthy subjects. Nine subjects (11%) had a median fasted gastric pH 〉5.0, and in five of these subjects the median pH remained 〉5.0 postprandially. In this group, drugs and dosage forms which require an acidic environment for dissolution or release may be poorly assimilated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018970323716
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  • 2
    Electronic Resource
    Electronic Resource
    Comparison of the Mechanism of Dissolution of Hydrocortisone in Simple and Mixed Micelle Systems (1993)
    Springer
    Pharmaceutical research 10 (1993), S. 865-870 
    Details
    ISSN: 1573-904X
    Keywords: hydrocortisone ; bile salts ; sodium taurocholate ; lecithin ; micelles ; dissolution rate ; solubility ; contact angles ; wetting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Lecithin, a major phospholipid component of human bile, is instrumental in the formation of mixed micelles in vivo, with implications for the dissolution and absorption of poorly soluble compounds administered orally. Hydrocortisone, a poorly aqueous soluble drug (S aq = 1.08 × 10−3 M), was chosen to compare the rate and mechanism of dissolution in a NaTC/lecithin (mixed micelle) system with its NaTC-only (simple micelle) counterpart. Surface tension, solubility studies, contact angles, rotating disk dissolution rates, and powder dissolution rates were compared for hydrocortisone between solutions containing NaTC/lecithin (4:1) and NaTC-only under conditions representative of the small intestine (0–30 mM NaTC, pH 5.5, 0.1 M NaCl). At all concentrations, the solubility of hydrocortisone in NaTC/lecithin was slightly higher (up to twofold) than in the corresponding NaTC-only solutions. At low NaTC concentrations, initial powder dissolution rates were faster in the NaTC/lecithin solutions than in corresponding NaTC-only solutions. In contrast, at high NaTC concentrations, initial powder dissolution rates in the NaTC-only solutions were faster. Results indicated that in the NaTC-only system wetting effects predominated for dissolution, while in the NaTC/lecithin system, the dissolution rate of hydro-cortisone was enhanced mainly via solubilization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018961227717
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  • 3
    Electronic Resource
    Electronic Resource
    pH-Related Changes in the Absorption of Dipyridamole in the Elderly (1994)
    Springer
    Pharmaceutical research 11 (1994), S. 136-143 
    Details
    ISSN: 1573-904X
    Keywords: elderly ; drug absorption ; gastric pH ; gastric emptying ; dipyridamole ; glutamic acid hydrochloride ; famotidine ; Heidelberg radiotelemetric capsule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The bioavailability of dipyridamole, a poorly soluble weak base, was evaluated in 11 healthy, older subjects (≥65 years), 6 with a low fasting gastric pH (control) and 5 with a fasting gastric pH 〉 5 (achlorhydric), in a randomized, crossover design. Subjects received 50 mg dipyridamole as a single oral dose both with and without pretreatment with 40 mg famotidine (control subjects) or 1360 mg glutamic acid HC1 (achlorhydric subjects). Gastric pH was monitored by Heidelberg radiotelemetric capsule. Gastric emptying of 99mTc-radiolabeled orange juice was measured. Gastric pH appeared to be a primary determinant in dipyridamole absorption in the elderly. Elevated gastric pH resulted in compromised dipyridamole absorption compared to low-gastric pH conditions in all cases. The administration of glutamic acid hydrochloride to achlorhydric subjects prior to the dose of dipyridamole corrected for the decreased C max and AUC(0–36) exhibited in achlorhydric subjects without pretreatment. Tmax and k a were slower in achlorhydrics, although pretreatment with glutamic acid HC1 tended to normalize these parameters. Based on these results, it would be beneficial for achlorhydrics to take glutamic acid hydrochloride prior to taking dipyridamole and other medications which need a low gastric pH for complete absorption. The administration of 40 mg famotidine was successful in elevating the gastric pH to 〉5 in all subjects and maintained it at 〉5 for at least 3 hr in all subjects tested. The lack of differences in C max and AUC(0–36) with significant differences in T max and k a indicated that control subjects after treatment with famotidine may serve as an adequate model for achlorhydrics with respect to the extent of absorption, but not with respect to the rate of absorption. Gastric emptying of a nutrient liquid was significantly slower in achlorhydric subjects than in control subjects. Finally, fasting serum gastrin appeared to be a relatively reliable and easy method for screening for achlorhydria in the elderly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018918316253
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  • 4
    Electronic Resource
    Electronic Resource
    Dissolution Testing as a Prognostic Tool for Oral Drug Absorption: Immediate Release Dosage Forms (1998)
    Springer
    Pharmaceutical research 15 (1998), S. 11-22 
    Details
    ISSN: 1573-904X
    Keywords: dissolution tests ; prediction of in vivo performance ; dissolution test conditions ; composition of dissolution media
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Dissolution tests are used for many purposes in the pharmaceutical industry: in the development of new products, for quality control and, to assist with the determination of bioequivalence. Recent regulatory developments such as the Biopharmaceutics Classification Scheme have highlighted the importance of dissolution in the regulation of post-approval changes and introduced the possibility of substituting dissolution tests for clinical studies in some cases. Therefore, there is a need to develop dissolution tests that better predict the in vivo performance of drug products. This could be achieved if the conditions in the gastrointestinal tract were successfully reconstructed in vitro. The aims of this article are, first, to clarify under which circumstances dissolution testing can be prognostic for in vivo performance, and second, to present physiological data relevant to the design of dissolution tests, particularly with respect to the composition, volume, flow rates and mixing patterns of the fluids in the gastrointestinal tract. Finally, brief comments are made in regard to the composition of in vitro dissolution media as well as the hydrodynamics and duration of the test.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011984216775
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  • 5
    Electronic Resource
    Electronic Resource
    Estimation of the Increase in Solubility of Drugs as a Function of Bile Salt Concentration (1996)
    Springer
    Pharmaceutical research 13 (1996), S. 163-167 
    Details
    ISSN: 1573-904X
    Keywords: poorly soluble drugs ; solubility ; bile salts ; sodium taurocholate ; partition coefficient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The objective of this study was to develop a model to predict the extent to which bile salts can enhance the solubility of a drug, based on the physicochemical properties of the compound. The ability to predict bile salt solubilization of poorly soluble drugs would be a key component in determining which drugs will exhibit fed vs. fasted differences in drug absorption. Methods. A correlation between the logarithm of the octanol/water partition coefficient [log P] of six steroidal compounds and their solubilities in the presence of various concentrations of sodium taurocholate at 37°C, log [SR] = 2.234 + 0.606 log [P] (r2 = 0.987) where SR is the ratio of the solubilization capacity of the bile salt to the solubilization capacity of water for the drug, was used to predict the solubility of five further compounds with diverse structures. The solubilities of the compounds in presence of sodium taurocholate were then measured. Results. The predicted solubilities were within 10% of the experimentally observed solubilities for griseofulvin, cyclosporin A and pentazocine. The model overpredicted the solubility of phenytoin and diazepam in 15 mM sodium taurocholate solution by a factor of 1.33 and 1.62 respectively. Conclusions. The expected increase in solubility as a function of bile salt concentration can be estimated on the basis of the partition coefficient and aqueous solubility of the compound.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016062224568
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  • 6
    Electronic Resource
    Electronic Resource
    Dissolution Testing as a Prognostic Tool for Oral Drug Absorption: Dissolution Behavior of Glibenclamide (2000)
    Springer
    Pharmaceutical research 17 (2000), S. 439-444 
    Details
    ISSN: 1573-904X
    Keywords: dissolution test ; glibenclamide ; bioequivalence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The dissolution behavior of two commercially availableglibenclamide formulations was tested in various media. The aim of thestudy was to investigate whether the use of biorelevant dissolutionmedia (BDM) would be advantageous over the use of standard mediafor predicting the in vivo performance of the two formulations.Methods. The dissolution tests were performed using USP 23 apparatus2. Conventional buffers and USP media were compared with two BDMcontaining different amounts of lecithin and sodium taurocholate.Results. The dissolution of two drug powders was highly dependenton wetting, particle size, pH, and the composition of the mediumused. In addition, the dissolution behavior of the two glibenclamideformulations showed differences in all media tested. The dissolutionresults of the two formulations were compared with those from anin vivo bioequivalence study undertaken by the central quality controllaboratory of the German pharmacists (ZL). The bioequivalencecriterion set by the ZL requires more than 80;pc drug release within 10minutes. Results in FaSSIF, one of the BDMs, met the ZL criterionand this medium was also able to discriminate between the twoformulations. This was not the case for the other media tested.Conclusions. The study indicates that BDM are better able to discriminatebetween glibenclamide formulations than standard dissolutionmedia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007529020774
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  • 7
    Electronic Resource
    Electronic Resource
    Comparison of Canine and Human Gastrointestinal Physiology (1986)
    Springer
    Pharmaceutical research 3 (1986), S. 123-131 
    Details
    ISSN: 1573-904X
    Keywords: drug absorption ; gastrointestinal tract, dogs ; gastrointestinal mobility and pH ; gastrointestinal drug absorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In this review, the gross physiology of the gastrointestinal tract of dogs is compared with that of humans, particularly as it pertains to drug absorption and dosage-form performance. Gastrointestinal (GI) motility and pH are the main parameters considered. Although similar motility patterns and pH profiles prevail in the two species for the most part, there are some differences that could affect the time profile and extent of drug absorption. These include slower gastric emptying in the fed state, faster small intestine transit, and higher and more variable intestinal pH in dogs compared with humans. An attempt is made to identify drug and dosage-form properties that would lead to differences in drug absorption in the two species, e.g., drug physicochemical properties, dosage-form size, and pH dependency of dosage-form release characteristics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016353705970
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  • 8
    Electronic Resource
    Electronic Resource
    Use of 1-Methyl-Pyrrolidone as a Solubilizing Agent for Determining the Uptake of Poorly Soluble Drugs (1999)
    Springer
    Pharmaceutical research 16 (1999), S. 968-971 
    Details
    ISSN: 1573-904X
    Keywords: itraconazole ; hydrocortisone, mannitol ; intestinal rings ; uptake mechanisms ; site-specific permeability ; l-Methyl-2-Pyrrolidone (NMP)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012120210530
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  • 9
    Electronic Resource
    Electronic Resource
    On the Use of the Quasi-Equilibrium Assumption for Drug Dissolution (1990)
    Springer
    Pharmaceutical research 7 (1990), S. 425-429 
    Details
    ISSN: 1573-904X
    Keywords: modeling ; drug dissolution ; quasi-equilibrium ; diffusion ; instantaneous reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The quasi-equilibrium assumption is often used to simplify the analysis of reaction diffusion problems, including those that arise in drug dissolution and ionization processes. This approximation often makes the governing equations tractable, and analytical solutions may then be obtained. However, the application of the quasi-equilibrium assumption may lead to simplified solutions that (1) are apparently inconsistent with stated boundary conditions and (2) have a physical interpretation that is different from those of the original problem statement. Herein we discuss these two issues as they arise in the modeling of drug dissolution processes. In spite of the different conceptualizations, the concentration profiles and dissolution fluxes obtained from the full and approximate solutions converge as the reaction response times exceed those of diffusion, thus supporting the applicability of the quasi-equilibrium assumption for ionized drug dissolution processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015892011092
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  • 10
    Electronic Resource
    Electronic Resource
    Letter to the Editor (1989)
    Springer
    Pharmaceutical research 6 (1989), S. 438-439 
    Details
    ISSN: 1573-904X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015999919521
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