Interaction between phenprocoumon and phytomenadion: a pharmacokinetic investigation in healthy volunteers

In 23 female and male healthy volunteers the pharmacokinetic behaviour of [3H]phenprocoumon and [3H]phytomenadion was investigated. The time-dependent changes in plasma radioactivity and the amount of urinary excretion were measured. Under simultaneous administration of phytomenadion (PHY) in daily doses of 10 mg, the elimination of phenprocoumon (PPC) was not altered (t0.5 beta 141.4 h, CUE50 20.4% of administered dose) as compared with data of previous investigations, while its anticoagulant effect was inhibited. PHY in doses of 10 mg was absorbed quickly and eliminated with a mean half-life of 60.6 h at a total body clearance (Cltot) of 9.3 ml/min and a renal clearance (Clren) of 1.9 ml/min. Under the co-administration of PPC the vitamin was eliminated with a half-life time of 23.1 h (Cltot 16.7 ml/min) and the amount of excreted radioactivity was enhanced (26.3% of administered dose; Clren 4.5 ml/min) as compared with the data of PHY without co-medication. From the experiments it is concluded that (1) PHY inhibits the action of PPC without influencing its pharmacokinetics, and (2) that PPC distinctly changes the pharmacokinetics of PHY and diminishes its pharmacodynamic action as measured by changes in the prothrombin complex activity.