Penbutolol Pharmacokinetics: the influence of concomitant administration of cimetidine

A possible interaction of penbutolol and cimetidine was investigated in healthy volunteers treated orally for 7 days. The plasma levels of unmetabolized penbutolol showed a slight but non-significant increase. The biphasic elimination kinetics of penbutolol (half-lives 0.8 and 17 h) was not affected by coadministration of cimetidine. Plasma levels of penbutolol were not significantly altered by chronic treatment with cimetidine, whereas the levels of 4-hydroxypenbutolol and 4-hydroxypenbutolol glucuronide were significantly reduced.