Drug Interaction Report

GENERALLY AVOID: Concurrent administration of guar gum may decrease the plasma levels of orally administered penicillins by reducing their absorption. In a study of 10 healthy volunteers administered phenoxymethyl penicillin with and without guar gum, both the peak serum concentration and the area under the serum concentration-time curve of penicillin were found to be significantly reduced by the gum.

MANAGEMENT: The use of guar gum should preferably be avoided during oral penicillin therapy. If these agents must be used together, separating the times of administration by as much as possible may help but has not been studied.

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.