Enzyme induction following a single dose of amobarbital in dogs

Dose-dependent pharmacokinetics: experimental observations and theoretical considerations

Clinically, absorption and elimination of most drugs follow linear kinetics, and pharmacokinetic parameters describing absorption and elimination of a drug do not change over the therapeutic dose range. However, dose-dependent pharmacokinetics have been reported more frequently in preclinical studies, particularly in toxicity studies, where high doses are often employed. This review highlights the major types of dose-dependent pharmacokinetics with unique examples. Before setting out on a pivotal subchronic and chronic toxicity study of a new drug, a pilot study is often performed to establish a dose range in which a reasonable relationship between plasma AUC and dosage exists to ensure sufficient exposure of animals to the drug. Theoretical bases and possible causes of dose-AUC disproportionality are discussed. Factors affecting the distribution and elimination of drugs and causes of dose-dependent tissue distribution and elimination are also discussed. Often, the non-linear kinetics complicate the design of dosage regimens and prediction of efficacy and toxicity. Thus, an understanding of the influence of dose on the pharmacokinetics is important in the evaluation of the efficacy and toxicity of new drugs.

Fractions metabolized in a triangular metabolic system: cinromide and two metabolites in the rhesus monkey

A previous study of the metabolic fate of cinromide (3-bromo-N-ethylcinnamamide) in rhesus monkey established that half of a dose is metabolized by N-deethylation to an active metabolite, 3-bromocinnamamide. Both cinromide and its proximal metabolite can be metabolized by amide hydrolysis to a second metabolite, 3-bromocinnamic acid, resulting in a triangular metabolic problem. This investigation was undertaken to distinguish between these two nonexclusive possibilites. A preliminary study was carried out to characterize the pharmacokinetics of 3-bromocinnamic acid. In the main study, six monkeys received an intravenous dose of cinromide, 3-bromocinnamamide, and 3-bromocinnamic acid in a randomized order. The time courses of compound administered and corresponding metabolites were followed. The following fractions of dose metabolized (mean +/- SD) were obtained: cinromide to 3-bromocinnamide: 0.53 +/- 0.24; 3-bromocinnamamide to 3-bromocinnamic acid: 0.53 +/- 0.21; cinromide to 3-bromocinnamic acid directly: 0.48 +/- 0.32. Thus, it was found that 3-bromocinnamic acid is formed directly from cinromide and from 3-bromocinnamamide. Also, as primary metabolites, 3-bromocinnamic acid and 3-bromocinamamide account for all of a cinromide dose with a mean value of 1.00 +/- 0.34. The observed variability in these fractions metabolized was explained by the fact that in the solution of the triangular metabolic problem, three clearances are assumed to remain constant over three studies.