Metformin use decreases the anticoagulant effect of phenprocoumon
Abstract
BACKGROUND: Anticoagulant therapy with vitamin K antagonists (VKAs) is affected by interaction of the VKAs with a large number of other drugs. Although metformin is generally not considered to interact with VKAs, we observed a decrease in INR after starting metformin treatment in patients using the VKA phenprocoumon.
OBJECTIVES: To investigate the influence of metformin use on the dosage of phenprocoumon and INR in stably anticoagulated patients.
PATIENTS: We used the database of the Anticoagulation Clinic Leiden for this study. In a population of 369 patients screened, 27 consecutive patients using phenprocoumon were prescribed metformin during the study period (1 January 2007 to 1 March 2009), without use of other concomitant medications or medical interventions that could influence the INR.
RESULTS: The mean phenprocoumon dosage increased from 2.13 to 2.37 mg per day within 6 weeks (mean increase, 0.23 mg; 95% CI, 0.12-0.34) and 2.49 mg per day within 3 months (mean increase, 0.36 mg; 95% CI, 0.24-0.48) after starting metformin. The mean INR decreased from 2.88 to 2.26 (mean decrease, 0.63; 95% CI, 0.41-0.85) within 6 weeks and 2.54 (mean decrease, 0.35; 95% CI, 0.24-0.48) within 3 months after starting metformin.
CONCLUSIONS: This study shows that clinicians should be aware that metformin treatment may lead to an increased optimal dosage of phenprocoumon.
How strong is the evidence?
Evidence Hub reads this as a cohort study, done in people. Its evidence level is 3 of 5 (Moderate · trial / cohort / secondary analysis). Trials without a large randomized design, cohorts and secondary analyses give moderate evidence. Reported size: 369 participants or records.
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