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Coumadin oral

Anticoagulants/Penicillinase Resistant Penicillins

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:

The cause of the interaction is not known. When these two medicines are taken together, your body may process your blood thinner more quickly.

What might happen:

The effect of your blood thinner may decrease.

What you should do about this interaction:

Contact your healthcare professionals (e.g. doctor or pharmacist) about taking these drugs together. If your doctor prescribes these drugs 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.Qureshi GD, Reinders TP, Somori GJ, Evans HJ. Warfarin resistance with nafcillin therapy. Ann Intern Med 1984 Apr;100(4):527-9.
2.Fraser GL, Miller M, Kane K. Warfarin resistance associated with nafcillin therapy. Am J Med 1989 Aug;87(2):237-8.
3.Davis RL, Berman W Jr, Wernly JA, Kelly HW. Warfarin-nafcillin interaction. J Pediatr 1991 Feb;118(2):300-3.
4.Shovick VA, Rihn TL. Decreased hypoprothrombinemic response to warfarin secondary to the warfarin-nafcillin interaction. DICP 1991 Jun; 25(6):598-600.
5.Kim KY, Frey RJ, Epplen K, Foruhari F. Interaction between warfarin and nafcillin: case report and review of the literature. Pharmacotherapy 2007 Oct;27(10):1467-70.
6.Taylor AT, Pritchard DC, Goldstein AO, Fletcher JL Jr. Continuation of warfarin-nafcillin interaction during dicloxacillin therapy. J Fam Pract 1994 Aug;39(2):182-5.
7.Heilker GM, Fowler JW Jr, Self TH. Possible nafcillin-warfarin interaction. Arch Intern Med 1994 Apr 11;154(7):822-4.
8.Lacey CS. Interaction of dicloxacillin with warfarin. Ann Pharmacother 2004 May;38(5):898.
9.Mailloux AT, Gidal BE, Sorkness CA. Potential interaction between warfarin and dicloxacillin. Ann Pharmacother 1996 Dec;30(12):1402-7.
10.Krstenansky PM, Jones WN, Garewal HS. Effect of dicloxacillin sodium on the hypoprothrombinemic response to warfarin sodium. Clin Pharm 1987 Oct; 6(10):804-6.
11.Halvorsen S, Husebye T, Arnesen H. Prosthetic heart valve thrombosis during dicloxacillin therapy. Scand Cardiovasc J 1999;33(6):366-8.
12.Khalili H, Nikvarz N, Najmeddin F, Dashti-Khavidaki S. A probable clinically significant interaction between warfarin and cloxacillin: three case reports. Eur J Clin Pharmacol 2012 Sep 4.
13.Marusic S, Gojo-Tomic N, Bacic-Vrca V, Franic M. Enhanced anticoagulant effect of warfarin in a patient treated with cloxacillin. Int J Clin Pharmacol Ther 2012 Jun;50(6):431-3.
14.Choi PY, Phillips KL, Rae I. High-dose intravenous flucloxacillin may affect warfarin therapy. Med J Aust 2011 Jun 6;194(11):613.
15.Merwick A, Hannon N, Kelly PJ, O'Rourke K. Warfarin-flucloxacillin interaction presenting as cardioembolic ischemic stroke. Eur J Clin Pharmacol 2010 Jun;66(6):643-4.
16.Garg A, Mohammed M. Decreased INR response secondary to warfarin-flucloxacillin interaction. Ann Pharmacother 2009 Jul; 43(7):1374-5.

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