The effect of halofenate or halofenate free acid on human, rat and guinea pig platelet aggregation.

Halofenate free acid (HFA), the major metabolite of the hypolipemic agent halofenate, blocked the secondary phase of human platelet aggregation induced by ADP, epinephrine, or thrombin; higher concentrations of clofibrate free acid (CFA) were required to produce similar inhibitory effects on platelet aggregation. HFA and CFA inhibited collagen-induced aggregation of human, rat, or guinea pig platelets. Halofenate orally administered to rats caused inhibition of collagen-induced aggregation when plasma levels of HFA exceeded 300 mug/ml, a clinically achievable human plasma concentration. The platelet inhibitory effects of clofibrate administration were less than those observed with halofenate administration.