Pharmacokinetics and Metabolism of Omeprazole in Man

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Abstract
Four studies of the pharmacokinetics and metabolism of omeprazole are briefly discussed. Two of these were carried out in young healthy subjects and indicated that about 54% of an oral dose is available to the systemic circulation. The distribution of omeprazole after an intravenous dose was consistent with localization of a major fraction of the drug in the extracellular water, with about 25% restricted to the blood. Omeprazole was rapidly cleared and possessed the characteristics of a high clearance drug; insignificant amounts of 14C-omeprazole were excreted by the kidneys, though metabolites were excreted very rapidly. Six different metabolites were reported, the major one being hydroxy-omeprazole. Increasing the intravenous dose of omeprazole from 10 mg to 40 mg had no significant effect on the pharmacokinetic parameters determined. A study in patients with impaired renal function showed that this had little effect on the kinetics of omeprazole, though excretion of metabolites was significantly affected. A study of elderly healthy subjects suggested that the disposition characteristics of omeprazole are affected to some extent by age; further studies are needed to elucidate the clinical implications. Omeprazole has been reported to prolong the half-life of diazepam which may be due to inhibition of the demethylation of diazepam. The interaction of omeprazole with the kinetics of aminopyrine and antipyrine was much less pronounced.