zantac-efferdose and Coumadin Interactions

Interactions between zantac-efferdose(ranitidine) and Coumadin (warfarin)

ranitidine and warfarin (Moderate Drug-Drug)

MONITOR: Limited data suggest that ranitidine may occasionally alter the hypoprothrombinemic effect of coumarin anticoagulants. There have been rare reports of altered prothrombin time or INR (both increases and decreases) during coadministration of ranitidine and warfarin. The mechanism of interaction is unknown. Ranitidine at usual therapeutic dosages has not been shown to significantly affect CYP450-mediated metabolism. Ranitidine also did not alter the pharmacokinetics or pharmacodynamics of warfarin in three out of four interaction studies. In the fourth study, oral clearance of a single dose of warfarin was reduced by 27% in five healthy subjects given ranitidine 150 mg twice a day for 7 days, and by more than 50% in two subjects given ranitidine 750 mg daily.

MANAGEMENT: Until more data are available, caution may be advisable if ranitidine is used in combination with coumarin anticoagulants. The INR should be checked regularly and anticoagulant dosage adjusted accordingly, particularly following initiation or discontinuation of ranitidine in patients who are stabilized on their anticoagulant regimen. Patients should be advised to promptly report any signs of bleeding to their doctor, including pain, swelling, headache, dizziness, weakness, prolonged bleeding from cuts, increased menstrual flow, vaginal bleeding, nosebleeds, bleeding of gums from brushing, unusual bleeding or bruising, red or brown urine, or red or black stools.