Drug Interaction Report

MONITOR: Theoretically, coadministration of trospium chloride with other drugs that are eliminated by active tubular secretion may result in increased plasma concentrations of trospium and/or the coadministered drug(s). The mechanism is competitive inhibition of renal excretion. Drugs that are thought to undergo active tubular secretion include acyclovir/valacyclovir, cidofovir, cimetidine, digoxin, flecainide, ganciclovir/valganciclovir, metformin, midodrine, morphine, pancuronium, procainamide, quinidine, ranitidine, tenofovir, triamterene, and vancomycin.

MANAGEMENT: Patients receiving trospium chloride in combination with other drugs that undergo active tubular secretion should be monitored for excessive pharmacologic effects of one or both drugs, and the dosages of the drugs adjusted if necessary.

ADJUST DOSING INTERVAL: Food may reduce the oral absorption and bioavailability of trospium chloride. According to the product labeling, administration of trospium chloride with a high fat meal reduced the peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) by 70% to 80% compared to administration while fasting.

MANAGEMENT: To ensure maximal oral absorption, trospium chloride should be administered at least 1 hour before meals or on an empty stomach. If trospium chloride is administered as a combination with xanomeline, the manufacturer recommends administering the capsules at least 1 hour before a meal or at least 2 hours after a meal. Capsules should be taken whole.

ADJUST DOSING INTERVAL: Oral products containing zinc such as mineral supplements and multivitamins may interfere with the gastrointestinal absorption of cephalexin, ceftibuten or cephradine. In one pharmacokinetic study (n=12), concurrent administration of zinc sulfate (250 mg, single oral dose) and cephalexin (500 mg, single oral dose) decreased cephalexin maximum concentration (Cmax) and systemic exposure (AUC; 0-inf) by 31.05% and 27.4%, respectively. However, in the same study, when zinc sulfate was administered 3 hours after the cephalexin dose, no significant alteration in cephalexin pharmacokinetics were observed.

MANAGEMENT: Oral medications or mineral supplements that contain zinc are recommended to be administered at least 3 hours after the cephalexin, ceftibuten or cephradine dose.