Development of optimal infusion regimens for epoprostenol using radio labelled platelet uptake over atherosclerotic lesions in man.

1. Epoprostenol (prostacyclin, PGI2) has been evaluated in clinical trials in peripheral vascular disease and other conditions chiefly on the basis of its platelet inhibitory properties. These therapeutic evaluations have proceeded in the absence of evidence as to the optimum infusion regimen for epoprostenol and the choice of schedules of administration has been arbitrary. We have tried to establish an optimum infusion regimen in patients with peripheral vascular disease in terms of maximal inhibition of platelet deposition on atherosclerotic lesions in vivo together with maximal inhibition of platelet aggregation ex vivo. 2. One hundred and twenty three patients with atherosclerotic peripheral vascular disease and increased platelet uptake at atherosclerotic sites were selected. Epoprostenol was administered at a fixed dose of 5 mg kg-1 min-1 for 0.5-24 h daily for 3-7 days. 3. Infusion of epoprostenol for 6 h daily for up to 5 days caused maximum decrease in platelet uptake without tachyphylaxis and without loss of the inhibitory effect of epoprostenol on platelet aggregation responses. Longer daily infusion periods were associated with progressive loss of the anti-aggregatory effect of epoprostenol without any greater decrease in platelet uptake. Shorter daily infusion periods produced smaller decreases in platelet uptake.