Drug Interaction Report

Concomitant administration of cimetidine may increase alfuzosin plasma concentrations. Multiple doses of cimetidine 1 gram daily iincreased alfuzosin Cmax and AUC by 20%. The mechanism and clinical significance are unknown.

ADJUST DOSING INTERVAL: Administration of alfuzosin with food enhances oral bioavailability. According to the manufacturer, extent of absorption is 50% higher when administered under fed conditions compared to fasting conditions.

MANAGEMENT: To ensure maximal oral absorption, alfuzosin should be administered with or immediately after a meal.

Concurrent use of cimetidine and ethanol may result in increased ethanol concentrations. The mechanism appears to be due to inhibition of gastric alcohol dehydrogenase by cimetidine, leading to increased bioavailability of the alcohol and inhibition of hepatic metabolism of alcohol. The clinical significance of this interaction is limited. More importantly, patients requiring cimetidine for gastrointestinal disease should be counseled to avoid alcohol to prevent worsening of their disease. The other H-2 receptor antagonists appear to have minimal effects on the concentrations of alcohol.

Caffeine effects may be increased in patients also taking cimetidine. The mechanism may be due to decreased caffeine metabolism induced by cimetidine. Although adequate clinical data are lacking, a reduction in dose or elimination of caffeine may be needed if excess CNS stimulation is observed.

H2 antagonists may reduce the clearance of nicotine. Cimetidine, 600 mg given twice a day for two days, reduced clearance of an intravenous nicotine dose by 30%. Ranitidine, 300 mg given twice a day for two days, reduced clearance by 10%. The clinical significance of this interaction is not known. Patients should be monitored for increased nicotine effects when using the patches or gum for smoking cessation and dosage adjustments should be made as appropriate.