Drug Interactions between cephalexin and Scopace

GENERALLY AVOID: Use of anticholinergic agents with alcohol may result in sufficient impairment of attention so as to render driving and operating machinery more hazardous. In addition, the potential for abuse may be increased with the combination. The mechanism of interaction is not established but may involve additive depressant effects on the central nervous system. No effect of oral propantheline or atropine on blood alcohol levels was observed in healthy volunteers when administered before ingestion of a standard ethanol load. However, one study found impairment of attention in subjects given atropine 0.5 mg or glycopyrrolate 1 mg in combination with alcohol.

MANAGEMENT: Alcohol should generally be avoided during therapy with anticholinergic agents. Patients should be counseled to avoid activities requiring mental alertness until they know how these agents affect them.

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.

The coadministration with grapefruit juice may delay the absorption and increase the bioavailability of oral scopolamine. The proposed mechanism is delay of gastric emptying as well as inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall induced by certain compounds present in grapefruits. In an open-label, crossover study consisting of 14 subjects, the consumption of grapefruit juice (compared to water) was associated with a 30% increase in mean systemic bioavailability and a 153% increase in time to reach peak serum concentration (Tmax) of scopolamine. However, the perceived pharmacodynamic effect of the drug, as measured by % change in subjective alertness compared to baseline, was similar after coadministration with water and grapefruit juice. Based on these findings, grapefruit juice is unlikely to affect the overall safety profile of of scopolamine but may delay its onset of action following oral administration. However, as with other drug interactions involving grapefruit juice, the pharmacokinetic alterations are subject to a high degree of interpatient variability.