The in vivo effect in humans of pyridoxal-5′-phosphate on platelet function and blood coagulation

Vitamin B 6 has an antithrombotic effect. This, based on the results of in vitro studies, has been attributed to an antiplatelet effect. We assessed the in vivo effect of vitamin B 6 by measuring the effect of long-term administration of vitamin B 6 on platelet function and blood coagulation. Vitamin B 6 (pyridoxine hydrochloride), 100mg twice daily p.o. for fifteen days, was administered to 10 healthy volunteers. The bleeding time was measured before the first dose and 15 days after. A baseline value, the acute effect, chronic effect, and the acute-on-chronic effect of vitamin B 6 was estimated by measuring platelet function. The following tests were performed: platelet aggregation induced by collagen, ADP and epinephrine; thromboxane A 2 (TxA 2)-production and prostacyclin inhibition of ADP-induced aggregation. The effects on the coagulation system were monitored by measuring: the prothrombin time, activated partial thromboplastin time and levels of coagulation factor. Vitamin B 6 significantly prolonged the bleeding time from 4.1 ± 1.1 minutes to 6.8 ± 1.0 minutes (p = 0.0063). Aggregation of platelets with collagen was slightly but not significantly inhibited. Platelet aggregation induced with the agonists ADP or epinephrine was significantly inhibited by vitamin B 6, and the platelets tended to aggregate at a slightly decreased rate. The mean TxA 2-production was slightly, but not significantly, decreased. Vitamin B 6 had no effect on the sensitivity of platelets to prostacyclin, or on the coagulation system. Our results indicate that the antithrombotic effects of vitamin B 6 is limited to inhibition of platelet function; there was no measurable influence on coagulation. The results of this in vivo study are however such that clinical trials are warranted to further assess the efficacy of vitamin B 6 as an antiplatelet drug.