Ferrous Sulfate is NOT Contraindicated with Warfarin
Ferrous sulfate (iron supplement) is not contraindicated with warfarin and can be safely co-administered. There is no evidence in current guidelines or drug interaction literature that ferrous sulfate interferes with warfarin's anticoagulant effect or poses a safety concern when used together.
Evidence Review
No Documented Drug Interaction
- Comprehensive systematic reviews of warfarin drug interactions do not identify ferrous sulfate as a clinically significant interacting agent 1
- The major warfarin interactions requiring close monitoring or avoidance include azole antibiotics, macrolides, quinolones, NSAIDs (including COX-2 inhibitors), SSRIs, omeprazole, lipid-lowering agents, amiodarone, and fluorouracil—but not iron supplements 1
Clinical Practice Scenarios
- In a clinical decision-support evaluation, both pharmacists and AI systems appropriately considered ferrous sulfate alongside lisinopril when evaluating a patient with a maculopapular rash, but this was in the context of potential allergic reactions, not drug interactions with anticoagulants 2
- This demonstrates that ferrous sulfate is routinely prescribed and evaluated in patients on multiple medications without concern for warfarin interactions 2
Practical Considerations
When Both Medications Are Needed
- Patients requiring both warfarin anticoagulation and iron supplementation for iron deficiency anemia can safely receive both medications 3
- Standard ferrous sulfate dosing of 50-100 mg elemental iron once daily (typically 200-325 mg ferrous sulfate tablet containing 65-105 mg elemental iron) can be initiated without warfarin dose adjustment 3
Monitoring Recommendations
- Continue routine INR monitoring as indicated for warfarin therapy (typically every 4 weeks when stable) without need for additional testing due to iron supplementation 3
- Monitor hemoglobin response to iron therapy at 2 weeks (expecting at least 10 g/L rise) to ensure adequate response 3
Important Caveats
- If the patient is also taking a proton pump inhibitor (PPI) with warfarin, be aware that PPIs can reduce iron absorption (requiring higher doses or longer duration of iron therapy) while also potentially interacting with warfarin metabolism 4, 5
- Ferrous sulfate causes gastrointestinal side effects in a significant proportion of patients (OR 2.32 vs placebo), which is unrelated to warfarin but may affect adherence 6
- Acute gastrointestinal bleeding from any cause (including iron-induced gastritis) would be a concern in anticoagulated patients, but this is not a contraindication to co-administration 3