The effects of a combined alpha- and beta-blocking drug, labetalol, on some aspects of platelet function

The effects of the combined alpha- and beta-adrenoreceptor blocking agent labetalol on human blood platelets as estimated by platelet aggregation, platelet count, bleeding time and platelet factor 3 activity were studied in 5 patients. The drug reduced adrenaline-induced platelet aggregation in vitro. However, it did not influence the above platelet function test in therapeutic plasma concentrations in vivo.