Drug Interaction Report

MONITOR: Limited data suggest that methylcellulose may interfere with the gastrointestinal absorption of pyridostigmine. The mechanism of interaction has not been established. In a study evaluating plasma pyridostigmine levels in 16 patients receiving pyridostigmine for myasthenia gravis, one subject who was also taking oral methylcellulose during the study was found to have undetectable pyridostigmine levels on two separate occasions. After stopping methylcellulose, the subject demonstrated a pattern of pyridostigmine in plasma similar to that of the other subjects. No other detail is available regarding the potential interaction.

MANAGEMENT: Caution may be advisable during concomitant use of pyridostigmine and methylcellulose. Consideration may be given to separating the times of administration by as much as possible or avoiding the use of methylcellulose if an interaction is suspected. It is not known if cellulose can also cause this interaction.

ADJUST DOSING INTERVAL: Bulk-forming laxatives such as guar gum, psyllium, polycarbophil, or methylcellulose may affect the bioavailability of concomitantly administered substances due to their effect on the rate of gastrointestinal transit and gastric emptying.

MANAGEMENT: In general, oral medications should be administered at least 2 hours before or 2 hours after dosing of the bulk-forming laxative.