Drug Interactions between entecavir and Sulfatrim

ADJUST DOSING INTERVAL: Food delays the oral absorption and reduces the oral bioavailability of entecavir. According to the product labeling, administration of entecavir 0.5 mg with a standard high-fat meal or a light meal resulted in a delay in absorption by 0.25 to 0.75 hours, a decrease in the peak plasma concentration (Cmax) by 44% to 46%, and a decrease in the area under the plasma concentration-time curve (AUC) by 18% to 20% compared to administration in the fasting state.

MANAGEMENT: To ensure maximal oral absorption, entecavir should be administered on an empty stomach at least 2 hours after a meal and 2 hours before the next meal.

MONITOR: Two cases have been reported in which patients on sulfamethoxazole-trimethoprim therapy, after consuming beer, reported flushing, heart palpitations, dyspnea, headache, and nausea (disulfiram - alcohol type reactions). First-generation sulfonylureas have been reported to cause facial flushing when administered with alcohol by inhibiting acetaldehyde dehydrogenase and subsequently causing acetaldehyde accumulation. Since sulfamethoxazole is chemically related to first-generation sulfonylureas, a disulfiram-like reaction with products containing sulfamethoxazole is theoretically possible. However, pharmacokinetic/pharmacodynamic data are lacking and in addition, the two reported cases cannot be clearly attributed to the concomitant use of sulfamethoxazole-trimethoprim and alcohol.

MANAGEMENT: Patients should be alerted to the potential for this interaction and although the risk for this interaction is minimal, caution is recommended while taking sulfamethoxazole-trimethoprim concomitantly with alcohol.