We report a doxepin-treated patient whose doxepin plasma levels were monitored before and during propoxyphene therapy. The pharmacokinetic interaction was further assessed by a study of antipyrine metabolism, used as a marker for drug oxidation, before and during propoxyphene treatment in healthy subjects. Impairment of antipyrine metabolism, used as a qualitative marker, provided evidence that increased doxepin and desmethyldoxepin levels shown in the elderly patient were the result of impaired oxidative drug metabolism. Propoxephene may inhibit human in-vivo oxidative drug metabolism in other cases as well, and this may explain in part the frequent morbidity and mortality seen when propoxyphene is concurrently taken with other oxidatively metabolized drugs.
ASJC Scopus subject areas
- Internal Medicine