Naproxen plasma levels in volunteers after single-dose administration by oral and rectal routes.

The bioavailability (plasma concentrations, AUC) of a rectal formulation (suppository) of naproxen was investigated in six healthy volunteers by comparison with an oral preparation (tablets). Plasma half-lives after both formulations were identical 10 hr 15 min+/-25 min (S.D.). Determined by the AUC the bioavailability of naproxen in the suppositories was 94.8%+/-6.3% of the bioavailability of naproxen in the tablets. This paper describes also a new gas-liquid chromatographic method for determining unchanged naproxen in human plasma which is quick, sensitive, and specific.