Clinical pharmacokinetics and oral bioavailability of ketobemidone

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Abstract
The basic pharmacokinetics and oral bioavailability of ketobemidone have been studied in 6 patients after surgery. Plasma concentrations were first determined following intravenous administration of Ketogin® 2 ml, containing ketobemidone chloride 10 mg and the spasmolytic N,N-dimethyl-3,3-diphenyl-1-methylallylamine chloride 50 mg, and then, on the second postoperative day, following oral administration of 2 tablets of Ketogin®, each containing ketobemidone chloride 5 mg and the spasmolytic agent 25 mg. The average oral bioavailability of ketobemidone was 34%±16% (SD, n=6). The mean plasma half-life of elimination (t1/2β) was about the same following oral (2.45±0.73 h; SD, n=5) as after intravenous administration (2.25±0.35 h; SD, n=6). The low oral bioavailability and rapid elimination of ketobemidone demonstrated in this study suggest that the usual dosage recommendation for oral Ketogin® (ketobemidone 5–10 mg every 6–7 h) in patients with severe pain is too low.