Single-dose kinetics and bioavailability of ketobemidone.

The single-dose kinetics and the oral and rectal bioavailability of ketobemidone have been studied in patients after surgery. Plasma concentrations were determined following intravenous administration of Ketogin 2 ml, containing ketobemidone chloride 10 mg and the spasmolytic substance N, N-dimethyl-3, 3-diphenyl-l-methylallylamine chloride 50 mg and following oral or rectal administration of Ketogin. Ketobemidone was analyzed by gas chromatography-mass spectrometry using a deuterated internal standard. Ketobemidone disappeared rapidly from plasma after i.v. or oral administration, yielding a mean plasma half-life between 2.25 and 2.45 h. After rectal administration the plasma half-life was somewhat prolonged (3.27 h), probably due to late absorption., The bioavailability of oral ketobemidone was 34% +/- 16% s.d. (n = 6), and when given rectally 44% +/- 9% s.d. (n = 5). In contrast to earlier investigations performed without plasma analysis, ketobemidone was found to have a rapid elimination when given intravenously, orally or rectally.