Why the study?
Do concomitant medications alter the response to oral anticoagulants?
Do concomitant medications alter the response to oral anticoagulants?
Concomitant use of various drugs can significantly alter the efficacy and safety of oral anticoagulants, necessitating careful monitoring to prevent bleeding or subtherapeutic anticoagulation.
May warrant close INR monitoring with interacting drugs; leaves open the need for prospective validation of interaction risks.
In recent years, a number of drugs have been identified which may alter the response to oral anticoagulants in man. Phenylbutazone and its congeners are probably the most widely recognized drugs capable of enhancing the hypoprothrombinemic action of oral anticoagulants. Other drugs which may enhance the anticoagulant response include acetaminophen, antibiotics, clofibrate, diphenylhydantoin, disulfiram, indomethacin, methylphenidate hydrochloride, methandrostenolone and norethandrolone, phenyramidol hydrochloride, quinidine and quinine, salicylates, thiouracils, and dextrothyroxine sodium. Conversely, barbiturates may decrease the anticoagulant effect of coumarin drugs and necessitate larger doses for effective anticoagulation. The failure to anticipate a reduced coumarin requirement when the barbiturate is discontinued may result in excessive anticoagulation. A similar effect has been demonstrated for the following drugs: antacids, chloral hydrate, cholestyramine resin, corticosteroids, ethchlorvynol, glutethimide, griseofulvin, haloperidol, meprobamate, and contraceptives administered orally. Mechanisms responsible for these interactions have been elucidated for a number of drugs.1-10Numerous case reports confirm bleeding complications
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Peter D. Kleinman (1970) studied this question.
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