Drug Interactions between amoxicillin / clarithromycin / omeprazole and guar gum

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.

Although some in vitro data indicate synergism between macrolide antibiotics and penicillins, other in vitro data indicate antagonism. When these drugs are given together, neither has predictable therapeutic efficacy. Data are available for erythromycin, although theoretically this interaction could occur with any macrolide. Except for monitoring of the effectiveness of antibiotic therapy, no special precautions appear to be necessary.

Clarithromycin may increase and prolong the omeprazole plasma concentration. The mechanism may be related to clarithromycin inhibition of hepatic cytochrome P450 enzymes responsible for omeprazole metabolism. Coadministration of omeprazole may result in an increase in clarithromycin and 14-(R)-hydroxyclarithromycin plasma concentrations. These increases may be due to the effect of omeprazole on gastric pH.