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.

ADJUST DOSING INTERVAL: Bowel cleansing products can increase the gastrointestinal transit rate. Oral medications administered within one hour of the start of administration of the bowel cleansing solution may be flushed from the gastrointestinal tract and not properly absorbed.

MANAGEMENT: Patients should be advised that absorption of oral medications may be impaired during bowel cleansing treatment. Oral medications (e.g., anticonvulsants, oral contraceptives, antidiabetic agents, antibiotics) should not be administered during and within one hour of starting bowel cleansing treatment whenever possible. However, if concomitant use cannot be avoided, monitoring for reduced therapeutic effects may be advisable.