Yohimbine Bioavailability in Humans

Pharmacokinetic profiles were determined in seven healthy young male subjects following single oral and intravenous doses of 10 mg of yohimbine hydrochloride. The drug was rapidly eliminated (t1/2 beta 0.58 h orally and t1/2 beta 0.68 h intravenously). Following intravenous administration the data fit a two-compartment pharmacokinetic model, with a very rapid distribution phase (t1/2a was approximately 6 min). Both the oral and the intravenous yohimbine clearance values were high but oral clearance values were much higher (mean 9.77 ml.min-1.kg-1 intravenous versus 55.9 ml.min-1.kg-1 oral). The oral bioavailability showed great variability, ranging from 7% to 87% (mean value was 33%). The incomplete oral bioavailability of yohimbine may reflect either incomplete absorption from the gastrointestinal tract or an hepatic first pass effect. Although yohimbine is rapidly absorbed when given orally, the bioavailability is quite variable and considerable individualization of dosing may be necessary when the drug is used orally for clinical indications.