The pharmacokinetics after intravenous and oral administration in man of the alpha 2-adrenoreceptor antagonist idazoxan (RX781094).

A high performance liquid chromatographic method was developed for the quantitative determination of idazoxan in plasma. The assay was used to study the disposition of the drug after intravenous infusion and oral administration to five normal subjects. After i.v. administration the kinetics could be described by a two compartment model with a mean elimination half life of 4.20 h. The mean calculated volume of distribution during the elimination phase was 3.20 l/kg-1 and the mean plasma clearance was 824 ml min-1. After oral administration a lag period before onset of absorption was observed in all five volunteers, the plasma levels declining monoexponentially from the peak concentration with a mean elimination half life of 5.58 h. The absolute availability varied between 26% and 41% with a mean value of 34%. In-vitro measurements produced a blood/plasma ratio of 1.3 for idazoxan.