INTERFERENCE WITH THE COAGULATION PROCESS MAY BE RESPONISBLE FOR THE INCREASED RISK OF HAEMORRHAGE WHEN ASPIRIN, CLOFIBRATE, OR THROID HORMONES ARE USED CONCOMITANTLY WITH ANTICOAGULANTS. NSAIDS INHIBIT PLATELET FUNCTION TO SOME EXTENT AND HAVE AN IRRITANT EFFECT ON THE G.I. TRACT, SO INCREASE THE RISK OF HAEMORRHAGE. ANTIBACTERIALS MAY INTERFERE WITH PLATELET FUNCTION OR WITH THE BACTERIAL SYNTHESIS OF VITAMIN K IN THE G.I. TRACT AND THUS HAVE AN ANTICOAGULANT EFFECT OF THEIR OWN. BARTITURATES SUCH AS PHENOBARBITONE AND PRIMIDONE DIMINISH THE ACTIVITY OF IT AND OTHER COUMARINS THROUGH INICREASED METABOLISM. CARBAMAZEPINE HAS A SIMILAR EFFECT. ( THE SAME CROSS REACTION OF WARFARIN THEN ALSO SEE WARFARIN CROSS REACTION).