Elevated international normalized ratio associated with concomitant warfarin and erlotinib
Kelly S Thomas1, Amanda Billingsley, Naseem Amarshi
1Central Arkansas Veterans Healthcare System, Little Rock, USA. kelly.thomas@va.gov
Summary
Erlotinib significantly increased International Normalized Ratio (INR) values in a patient taking warfarin for atrial fibrillation and lung cancer. This drug interaction led to elevated INR and hematoma, requiring medical intervention.
Area of Science:
- Oncology
- Pharmacology
- Hematology
Background:
- A 47-year-old male with advanced lung cancer and atrial fibrillation was treated with warfarin for venous thromboembolism.
- Warfarin dosage was managed to maintain a target INR of 2-3, with stable values for over eight weeks prior to erlotinib initiation.
Observation:
- Erlotinib was initiated as part of the patient's chemotherapy regimen for non-small-cell lung cancer.
- Within seven days of starting erlotinib, the patient's INR increased from 2.8 to 5.3, despite no changes in warfarin dosage, diet, or other medications.
Findings:
- A further increase in INR to 9.1 occurred after withholding warfarin doses, leading to the development of an elbow hematoma.
- Anticoagulation was reversed with phytonadione, and erlotinib was discontinued, resulting in a rapid normalization of INR values.
Implications:
- This case highlights a significant drug interaction between erlotinib and warfarin, leading to supratherapeutic anticoagulation.
- Clinicians should closely monitor INR levels in patients receiving concomitant warfarin and erlotinib therapy.
- Awareness of this interaction is crucial for managing anticoagulation in cancer patients undergoing treatment with these medications.
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