Drug Interactions between Duexis and Fish Oil

MONITOR: Omega-3 fatty acids (e.g., fish oil) may potentiate the pharmacologic effects of anticoagulants and other drugs that affect hemostasis such as platelet inhibitors, thrombin inhibitors, thrombolytic agents, dextran, and nonsteroidal anti-inflammatory drugs (NSAIDs). The exact mechanism of interaction is unknown. Omega-3 fatty acids may possess mild antiplatelet and hypocoagulant activities. In some studies, these substances have been shown to reduce thrombin generation and plasma levels of fibrinogen, prothrombin, and coagulation factors V, VII, and X. Prolongation of bleeding time has been demonstrated, although it did not exceed normal limits and did not produce clinically significant bleeding. The interaction was suspected in a case report of a 67-year-old woman treated with warfarin for 1.5 years who exhibited an increase in INR from 2.8 the previous month to 4.3 approximately one week after doubling her fish oil dosage from 1000 to 2000 mg/day. Prior to the increase, her INR had been stable and therapeutic for 5 months on warfarin 1.5 mg/day. The patient was advised to reduce her fish oil consumption to 1000 mg/day, while her warfarin dose was withheld for one day and then reduced to 1 mg alternating with 1.5 mg per day. Eight days later, her INR was subtherapeutic at 1.6, so the warfarin dosage was increased back to 1.5 mg/day. The patient's INR subsequently returned to therapeutic range.

MANAGEMENT: In general, patients should consult a healthcare provider before taking any herbal or nutritional supplements. Patients using omega-3 fatty acids in combination with anticoagulants or other drugs that affect hemostasis should be advised of the potential for increased risk of bleeding complications.

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H2 antagonists may alter the disposition of nonsteroidal anti-inflammatory drugs (NSAIDs), resulting in increased or decreased plasma concentrations. Data are varied, even for the same NSAID. The mechanism may be related to inhibition of metabolism, changes in gastric pH that decrease absorption, and/or reduced urinary elimination. Statistically significant changes have been small and of limited clinical significance. Clinical monitoring of patient response and tolerance is recommended.

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