Stirring the Pot: Potential Drug Interactions With Marijuana

Warfarin. A single published case report describes an interaction with a patient taking warfarin who also regularly smoked tobacco and marijuana. The patient had multiple comorbidities and was taking at least 10 other medications. On at least two occasions, the patient’s international normalized ratio (INR) increased to values over 10 with episodes of bleeding. The only change reported for both occasions was an increase in the amount and frequency of marijuana smoking.[24] Patients who take warfarin and use marijuana regularly should receive close INR monitoring for any potential interaction.

Antiepileptic drugs (AEDs). A recent study examined baseline serum AED levels to identify drug-drug interactions between CBD and 19 AEDs during an open-label safety study in 81 patients (39 adults, 42 children) with refractory epilepsy.[25] As doses of CBD were increased, the researchers noted an increase in the serum levels of topiramate (P<.01), rufinamide (P<.01), and desmethylclobazam (P<.01) and a decrease in the levels of clobazam (P<.01) in both adult and pediatric patients. In adult patients, a significant increase in the serum levels of zonisamide (P=.02) and eslicarbazepine (P=.04) was observed with increasing CBD dose. No other drug interactions among the 19 AEDs were noted.   The authors recommended monitoring serum AED levels in patients receiving CBD, as drug-drug interactions may be correlated with adverse events and laboratory abnormalities.

Patients using marijuana should be educated to avoid drugs that affect associated CYP450 enzymes. When these drugs cannot be avoided, and marijuana use is expected to continue, the patient should be monitored closely for potential drug interactions.   Be Aware and Educate Patients

Smoking more than two joints weekly is likely to increase the risk for drug-related interactions.[5,10] No data exist monitoring large-scale marijuana use in the United States. However, in Washington, a state in which marijuana use is legal, the average user is estimated to smoke two to three joints per week.[26]  With growing legalization and use throughout the nation, healthcare professionals must exercise heightened caution in the situation of concomitant use of medications and marijuana.

Source:: Stirring the Pot: Potential Drug Interactions With Marijuana – Medscape – Jun 08, 2017.  http://www.medscape.com/viewarticle/881059#vp

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