A comparison of the effects of three positive inotropic agents (amrinone, milrinone and medorinone) on platelet aggregation in human whole blood

Amrinone, milrinone and medorinone inhibit platelet aggregation in human whole blood. They are particularly potent inhibitors of arachidonic acid induced aggregation, inhibiting by 50% (IC₅₀) at concentrations of 1.5μM (milrinone), 7.5μM (medorinone) and 48μM (amrinone). Each drug was less potent at inhibiting ADP and collagen-induced aggregation. The rank order for inhibition of arachidonic acid - induced aggregation correlated well with the rank order of cyclic AMP phosphodiesterase inhibition for these drugs when coupared to the response of a reference cAMP phosphodiesterase inhibitor (CI-930) and a reference cAMP phosphodiesterase inhibitor (M & B 22948). Since inhibition of platelet aggregation occurred at clinically relevant concentrations, it is evident that these agents have potentially beneficial antithrombotic properties.