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This information is generalized and not intended as specific medical advice. Consult your healthcare professional before taking or discontinuing any drug or commencing any course of treatment.

Medical warning:

Serious. These medicines may interact and cause very harmful effects. Contact your healthcare professional (e.g. doctor or pharmacist) for more information.

How the interaction occurs:

When these two medicines are taken together, the barbiturate may cause your body to process the blood-thinner more quickly.

What might happen:

The effect of the blood-thinner may decrease.There is an increased chance of bleeding if you are taking these medicines together and you stop taking the barbiturate. You may experience bleeding from your gums, nose bleeds, unusual bruising, or dark stools.

What you should do about this interaction:

Contact your healthcare professionals (e.g. doctor or pharmacist) as soon as possible about taking these two medicines together. If your doctor prescribes these medicines together, you may need to check your bleeding times more often.Your healthcare professionals may already be aware of this interaction and may be monitoring you for it. Do not start, stop, or change the dosage of any medicine before checking with them first.


1.Levy G, O'Reilly RA, Aggeler PM, Keech GM. Pharmacokinetic analysis of the effect of barbiturate on the anticoagulant action of warfarin in man. Clin Pharmacol Ther 1970 May-Jun;11(3):372-7.

2.Goss JE, Dickhaus DW. Increased bishydroxycoumarin requirements in patients receiving phenobarbital. N Engl J Med 1965 Nov 11;273(20):1094-5.

3.MacDonald MG, Robinson DS. Clinical observations of possible barbiturate interference with anticoagulation. JAMA 1968 Apr 8;204(2):97-100.

4.Lucas ON. Study of the interaction of barbiturates and dicumarol and their effect on prothrombin activity, hemorrhage, and sleeping time in rats. Can J Physiol Pharmacol 1967 Sep;45(5):905-13.

5.Aggeler PM, O'Reilly RA. Effect of heptabarbital on the response to bishydroxycoumarin in man. J Lab Clin Med 1969 Aug;74(2):229-38.

6.Breckenridge A, Orme M. Clinical implications of enzyme induction. Ann N Y Acad Sci 1971 Jul 6;179:421-31.

7.Johansson SA. Apparent resistance to oral anticoagulant therapy and influence of hypnotics on some coagulation factors. Acta Med Scand 1968 Oct;184(4):297-300.

8.Welch RM, Harrison YE, Conney AH, Burns JJ. An experimental model in dogs for studying interactions of drugs with bishydroxycoumarin. Clin Pharmacol Ther 1969 Nov-Dec;10(6):817-25.

9.Antlitz AM, Tolentino M, Kosai MF. Effect of butabarbital on orally administered anticoagulants. Curr Ther Res Clin Exp 1968 Feb;10(2):70-3.

Selected from data included with permission and copyrighted by First Databank, Inc. This copyrighted material has been downloaded from a licensed data provider and is not for distribution, expect as may be authorized by the applicable terms of use.

CONDITIONS OF USE: The information in this database is intended to supplement, not substitute for, the expertise and judgment of healthcare professionals. The information is not intended to cover all possible uses, directions, precautions, drug interactions or adverse effects, nor should it be construed to indicate that use of a particular drug is safe, appropriate or effective for you or anyone else. A healthcare professional should be consulted before taking any drug, changing any diet or commencing or discontinuing any course of treatment.

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