Drug Interaction Report

Anticholinergic agents may increase the absorption and oral bioavailability of nitrofurantoin. The proposed mechanism involves increased gastrointestinal transit time due to reduction of stomach and intestinal motility by anticholinergic agents. In six healthy volunteers, pretreatment with propantheline 45 minutes before a single 100 mg dose of nitrofurantoin significantly increased the oral bioavailability of nitrofurantoin as indicated by a 68% increase in urinary recovery. In another study, atropine 500 mcg given subcutaneously one-half hour before a single 100 mg dose of nitrofurantoin delayed the absorption and urinary excretion of nitrofurantoin but did not affect its overall bioavailability in ten healthy volunteers. The clinical significance of these changes is unknown.

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.