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  • 1
    ISSN: 1573-904X
    Keywords: sumatriptan ; gastrointestinal tract ; absorption ; metabolism ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sumatriptan exhibits low oral bioavailability partly due to presystemic metabolism, which may vary with regional differences in metabolic activity throughout the gastrointestinal tract. This study evaluated sumatriptan absorption in humans after administration orally and by oroenteric tube into the jejunum and cecum. Because the site of cecal administration varied, pharmacokinetic parameters for sumatriptan and its major metabolite were compared statistically only after oral and jejunal administration. One-half of the oral dose was recovered in the urine as parent (3%) and metabolite (46%). Sumatriptan was absorbed throughout the gastrointestinal tract; absorption was similar after oral and jejunal administration, and less after cecal administration. The metabolite AUC and the AUC ratio (metabolite/parent) were significantly lower after jejunal compared to oral administration; the AUC ratio was two-fold lower after cecal administration. Results suggest that presystemic metabolism of sumatriptan varies throughout the gastrointestinal tract and/or regional differences exist in the absorption of metabolite formed within the gastrointestinal tract.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-904X
    Keywords: ranitidine ; effervescent tablet ; absorption ; bioavailability ; bioequivalence ; sodium acid pyrophosphate ; gastrointestinal transit time
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract During development of a ranitidine effervescent oral solution dosage form, a marked decrease was observed in the extent of ranitidine absorption relative to the conventional oral tablet. Two studies were conducted in healthy volunteers to confirm the involvement of an excipient, SAPP (sodium acid pyrophosphate), and the mechanism of interaction, altered gastrointestinal transit. The first study (n = 12) involved single-dose crossover comparisons of (A) 150 mg ranitidine with 1132 mg SAPP versus (B) 150 mg ranitidine and (C) 150 mg ranitidine with all the effervescent tablet excipients except SAPP versus (D) a 150-mg ranitidine effervescent tablet, all administered as oral solutions. Serum ranitidine AUC, C max, and t max were compared using two one-sided t test 90% confidence intervals (CI). Comparing treatments A to B and D to C, all 90% CI were below the 80–120% range, indicating significantly less extensive ranitidine absorption (54% based on AUC) from the oral solutions containing SAPP. The second study (n = 12) was a single-dose crossover comparing 50 µCi 111InCl solutions with and without 1132 mg SAPP. Gastrointestinal transit times, determined by scintigraphic imaging, were compared between treatments. Gastric emptying time was unchanged, but small intestinal transit time was decreased to 56% in the presence of SAPP. More rapid small intestinal transit associated with an excipient of a solution dosage form apparently resulted in a decreased extent of ranitidine absorption. This observation contradicts the conventional wisdom that oral solutions are unlikely to fall short of bioequivalence relative to solid oral formulations.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-904X
    Keywords: diazepam ; phenytoin ; ACC-9653 ; prodrug ; protein binding ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The protein binding and pharmacokinetics of diazepam, ACC-9653 (a phenytoin prodrug), and phenytoin were evaluated in nine healthy male volunteers following administration of diazepam and ACC-9653, alone or concomitantly, in a randomized crossover design. No significant differences were observed in the fraction unbound or pharmacokinetic parameters of ACC-9653, phenytoin, or diazepam when ACC-9653 was administered alone compared to concomitant administration with diazepam. The phenytoin fraction unbound increased significantly with increased concentrations of ACC-9653, indicating displacement of phenytoin from its binding sites by ACC-9653. ACC-9653 also demonstrated concentration dependent binding. The lack of a significant pharmacokinetic drug interaction between ACC-9653 and diazepam suggests that these drugs may be safely administered together, although this conclusion should be confirmed in the intended patient population.
    Type of Medium: Electronic Resource
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