Warfarin dose adjustment required after cannabidiol initiation and titration.

Purpose: A case of a possible interaction between cannabidiol and warfarin is presented along with a brief overview of cytochrome enzymes involved in these drugs' metabolism.
Summary: A 46-year-old male taking warfarin for treatment of a deep venous thrombosis was initiated on a Food and Drug Administration (FDA)-approved cannabidiol product (Epidiolex, Greenwich Biosciences) for intractable epilepsy. The patient's International Normalized Ratio (INR) was monitored closely during cannabidiol initiation and dose titration. The patient required a nearly 20% warfarin dose reduction to maintain an INR within the goal range after starting therapy with cannabidiol. There is 1 other case report describing a clinically significant interaction between cannabidiol (specifically Epidiolex) and warfarin in a patient receiving warfarin who was enrolled in a study involving the initiation and titration of cannabidiol; that patient developed a supratherapeutic INR of 6.86 and required a 30% reduction in the weekly warfarin dose to reachieve the goal INR.
Conclusion: A previously published report suggesting an interaction between cannabidiol and warfarin is supported by this case report. INR should be monitored frequently in patients taking warfarin who begin to take FDA-approved cannabidiol. Additional studies should be performed to clarify the interaction potential of cannabidiol and warfarin.
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