Drug Interaction Report

MONITOR: Coadministration with inhibitors of CYP450 2C8 and/or 2C9 may increase the plasma concentrations of montelukast, which is metabolized by these isoenzymes in addition to CYP450 3A4. When montelukast was administered with the potent CYP450 2C8/2C9 inhibitor gemfibrozil, montelukast systemic exposure (AUC) increased by 4.4-fold. The addition of itraconazole, a potent CYP450 3A4 inhibitor, to gemfibrozil and montelukast did not further increase the AUC of montelukast. Administration of itraconazole alone with montelukast also resulted in no significant increase in the AUC of montelukast, which would suggest that montelukast is primarily metabolized by CYP450 2C8 and 2C9 in vivo.

MANAGEMENT: According to the product labeling, no dosage adjustment of montelukast is required when used in combination with gemfibrozil. However, it may be advisable to monitor patients for potentially increased adverse effects during coadministration with gemfibrozil or other CYP450 2C8/2C9 inhibitors.

MONITOR: Coadministration with inhibitors of CYP450 2C8 and/or 2C9 may increase the plasma concentrations of montelukast, which is metabolized by these isoenzymes in addition to CYP450 3A4. When montelukast was administered with the potent CYP450 2C8/2C9 inhibitor gemfibrozil, montelukast systemic exposure (AUC) increased by 4.4-fold. The addition of itraconazole, a potent CYP450 3A4 inhibitor, to gemfibrozil and montelukast did not further increase the AUC of montelukast. Administration of itraconazole alone with montelukast also resulted in no significant increase in the AUC of montelukast, which would suggest that montelukast is primarily metabolized by CYP450 2C8 and 2C9 in vivo.

MANAGEMENT: According to the product labeling, no dosage adjustment of montelukast is required when used in combination with gemfibrozil. However, it may be advisable to monitor patients for potentially increased adverse effects during coadministration with gemfibrozil or other CYP450 2C8/2C9 inhibitors.

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.