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Metformin use decreases the anticoagulant effect of phenprocoumon
J C F Wijnen1, I R van de Riet, W M Lijfering
1Anticoagulation Clinic, Leiden University Medical Center, Leiden, the Netherlands.
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.
Insights
Metformin use in patients on phenprocoumon (a vitamin K antagonist) requires increased phenprocoumon dosage to maintain therapeutic INR levels. Clinicians should monitor patients closely when initiating metformin during VKA therapy.
Area of Science:
- Pharmacology
- Clinical Medicine
- Drug Interactions
Background:
- Vitamin K antagonist (VKA) anticoagulant therapy is susceptible to drug interactions.
- Metformin is not typically associated with VKA interactions.
- A decrease in INR was observed in patients taking phenprocoumon when metformin was initiated.
Purpose of the Study:
- To assess the impact of metformin on phenprocoumon dosage and INR in patients on stable anticoagulation.
- To investigate potential drug interactions between metformin and phenprocoumon.
Main Methods:
- Retrospective analysis of patient data from Anticoagulation Clinic Leiden.
- Inclusion of 27 patients on phenprocoumon who were prescribed metformin.
- Exclusion of patients with other interacting medications or interventions.
Main Results:
- Mean phenprocoumon dosage increased by 0.23 mg/day within 6 weeks and 0.36 mg/day within 3 months after starting metformin.
- Mean INR decreased by 0.63 within 6 weeks and 0.35 within 3 months after initiating metformin.
- These changes indicate a reduced anticoagulant effect of phenprocoumon during metformin co-administration.
Conclusions:
- Metformin therapy necessitates an increased phenprocoumon dosage to achieve and maintain therapeutic INR.
- Clinicians must be vigilant for this interaction and adjust phenprocoumon dosage accordingly.
- Awareness of this interaction is crucial for safe and effective VKA anticoagulation management.
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