ORALLY ADMINISTERED VITAMIN B PROLONGS THE BLEEDING TIME AND INHIBITS PLATELET AGGREGATION IN HUMAN VOLUNTEERS.

Abstract

It is known that mM concentrations of vitamin B6 inhibit human platelet aggregation and fibrin formation in vitro. There are very few and controversial data on the ex vivo effects of vitamin B6 on hemostatic parameters. We evaluated the effects of oral administration of vitamin B6 on bleeding time (BT), fibrin formation, platelet aggregation (PA) and the release reaction (RR). Vitamin B6 300 mg/day p.o., was given to 18 healthy volunteers (8 M, 10 F, aged 23-35) for 8 days. BT was measured before the first dose (Baseline), 2 hr after the first (Day 1) and the last dose (Day 8). In 7 subjects BT was measured also 7 days after the suspension of the drug (Day 15). Before and 2 hr after the first dose, prothrombin time (PT), partial thromboplastin time (PTT), thrombin time (TT), PA and the RR induced by different concentrations of ADP, PAF-acether, collagen (coll), epinephrine (epi), arachidonate (AA) were studied. BT was significantly prolonged after vitamin B6 administration, and returned to baseline values 7 days after suspension of the drug. PA and the RR induced by 1 uM ADP, 1 ug/ml coll or 5 uM epi were significantly inhibited 2 hours after vitamin B6 administration. Vitamin B6, however, did not affect PA or the RR induced by 0.2-2 uM PAF-acether, 2 uM ADP, 1 mM AA, 2 ug/ml coll, nor did it affect PT, PTT or TT. These data show that orally administered vitamin B impairs primary hemostasis, but does not affect fibrin 6 formation, as measured with standard coagulation tests.