Inhibition of platelet aggregation by ketamine hydrochloride

Ketamine hydrochloride, 10 mg/kg by intramuscular injection, inhibited aggregation of platelets from three out of three baboons. Aggregation to ADP, arachidonic acid, epinephrine, and collagen was inhibited but aggregation to ristocetin was normal. Two baboons anaesthetised with the related drug phencyclidine, 1.0 mg/kg intramuscularly, had delayed aggregation. Ketamine inhibition of human platelets was irreversible in that aggregation could not be restored by either gel filtration of inhibited platelets and the re-addition of normal plasma, or by increasing the concentrations of agonists. Mixtures of human ketamine inhibited and aspirinised platelets failed to aggregated. Thromboxane B2 production was reduced to 3% of the amount produced by non inhibited platelets but the oxygen burst was not inhibited.