?-9-tetrahydrocannabinol dose increase leads to warfarin drug interaction and elevated INR

ObjectiveWe have reported a case of drug-drug interaction (DDI) involving warfarin and ?-9-tetrahydrocannabinol (THC) that resulted in supratherapeutic international normalized ratio (INR) level. The purpose this report is to highlight the possibility pharmacokinetic DDI between THC warfarin.Case summaryA 67-year-old Caucasian man suffering from chronic pain presented dispensary Buffalo, NY, for refill his medical cannabis (MC). patient asked speak with pharmacist, during their discussion stated he had INR level 5.2 measured at home self-test device. no evidence bleeding, administration was held 2 days before returned normal range. occurred when self-titrating dose scored an 8, or “probable,” on Naranjo Adverse Drug Effect Probability Scale.Practice implicationsWarfarin cannabinoids such as are both metabolized by cytochrome P450 (CYP) isozymes present liver gastrointestinal tract. In described, increase 7.35 mg preceded elevation 5.2, but did not result any bleeding. These observations suggestive THC. Clinicians involved MC should adequate knowledge drugs act substrates, inhibitors, inducers CYP enzymes, including major cannabinoids.