Drug Interaction Report

CONTRAINDICATED: Some sulfonamides can form an insoluble precipitate with formaldehyde, which is generated from the hydrolysis of methenamine in acidic urine maintained by the presence of hippuric acid.

MANAGEMENT: Methenamine preparations should not be given to patients taking sulfonamides due to the risk of crystalluria. An alkalinizing agent should not be added because this may render methenamine less effective.

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.