Pharmacokinetics of phenprocoumon in the horse. Contribution to anticoagulant therapy.

: The pharmacokinetics of racemic phenprocoumon were studied in 8 adult horses after the single intravenous and oral administration of 0.75 mg/kg. After i.v. administration the plasma concentration of phenprocoumon showed a biphasic decline in time. The pharmacokinetics were calculated on the two-compartment open model. The average plasma half-life (beta-phase) was 22 hours, the apparent volume of distribution was 0.61 l/kg, Cltot was 25.2 ml/kg/h (13.9-40.9 ml/kg/h). The systemic bioavailability of oral phenprocoumon was 97.6%, Tmax was found to be 4-12 hours. The effect of phenprocoumon on the coagulation system was determined by the activity of Factor X, the Quick's one stage prothrombin time and the PTT. Factor X showed the most marked effect. A reduction of the content of Factor X was seen over 7-9 days, it decreased to 11-33%. Quick's one stage prothrombin time was reduced over 4-8 days, the lowest values were 22-55%. The PTT showed only a small reaction on the single administration of 0.75 mg/kg phenprocoumon. Differences in the effect on the coagulation between the i.v. and the oral administration could not be observed. In comparison to warfarin, phenprocoumon showed a longer t0.5 (beta) and produced a markedly longer hypothrombogenic reaction. Therefore phenprocoumon appeared to be more suitable for a long term anticoagulation therapy in horses than the structurally related warfarin.