A monoclonal antibody that recognizes the GPIIb/IIIa antagonist DMP 728. Reversal of the effects of DMP 728 on platelet aggregation and bleeding time in the dog

Antiplatelet effects of MK-852, a platelet fibrinogen receptor antagonist, in healthy volunteers

MK-852, a cyclic heptapeptide, is a potent platelet fibrinogen receptor antagonist. When administered to normal healthy male subjects by 1- and 4-hour constant rate intravenous infusions, it provides a generally well-tolerated and reversible means of inhibition of platelet function. At infusion rates of 1 microgram/kg/min for 1 hour and 0.44 microgram/kg/min for 4 hours, respectively, MK-852 extended baseline bleeding time by greater than 2.2-fold and 2.6-fold, inhibited ADP-induced platelet aggregation by 76% and 69%, and inhibited collagen-induced platelet aggregation by 65% and 67%, respectively. The pharmacokinetics of MK-852 include an elimination half-life of approximately 2 hours, total clearance of about 150 ml/min, and volume of distribution of about 18 liters. Examination of the relationship between MK-852 whole-blood concentration in vitro and inhibition of platelet aggregation showed an EC50 of about 55 ng/ml and a Hill coefficient of 1.55. The infusions were generally well tolerated, with no study drug-related changes in blood counts or biochemical profiles.

Tirofiban provides "platelet anesthesia" during cardiopulmonary bypass in baboons

OBJECTIVE

Tirofiban (Aggrastat) is a reversible, nonpeptide inhibitor of platelet glycoprotein II/IIIa receptors. We tested the hypothesis that tirofiban preserves platelet number and function and shortens postoperative bleeding times in baboons after cardiopulmonary bypass.

METHODS

Four groups were studied: control, n = 12; low-dose tirofiban (0.1 microg/kg per minute), n = 7; high-dose tirofiban (0.3 microg/kg per minute), n = 7; and bolus tirofiban (15 microg/kg) followed by 0.1 microg/kg per minute during cardiopulmonary bypass, n = 7. After heparin, animals were perfused for 60 minutes at 50 ml/kg per minute and 37 degrees C with a bubble oxygenator, roller pump, and peripheral cannulation. Hemodynamics, platelet count, platelet aggregation to adenosine diphosphate, and release of beta-thromboglobulin were measured before tirofiban infusion, before heparin, after heparin before bypass, after 5 and 55 minutes of bypass, after protamine, and 60 minutes after protamine. Template bleeding times were measured at the same times except during cardiopulmonary bypass and 120 and 180 minutes after protamine administration. Platelet glycoprotein IIIa antigen was measured in Triton X-100 washes (Sigma Chemical Company) of the perfusion circuit after bypass.

RESULTS

High-dose tirofiban completely prevents platelet loss during cardiopulmonary bypass. beta-Thromboglobulin release and sensitivity to adenosine diphosphate are significantly less than control at the end of bypass in all tirofiban groups. Template bleeding times return to preoperative values in both the low- and high-dose tirofiban groups 180 minutes after protamine administration and are significantly less than control bleeding times at both 120 and 180 minutes after protamine. Surface glycoprotein IIIa antigen does not significantly differ between groups.

CONCLUSION

High-dose tirofiban completely preserves platelet number and improves platelet function during cardiopulmonary bypass in baboons and significantly accelerates restoration of normal template bleeding times after bypass.