Drug Interactions between gemifloxacin and Videx EC

ADJUST DOSING INTERVAL: Concomitant administration with didanosine buffered tablets or pediatric oral solution may reduce the oral bioavailability of gemifloxacin and other quinolone antibiotics. The mechanism is reduced quinolone absorption due to chelation with metallic cations from buffering agents and antacids used in certain formulations of didanosine. According to the product labeling, the peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of gemifloxacin were reduced by 87% and 85%, respectively, during concomitant administration of an aluminum- and magnesium-containing antacid. Administration of the antacid or ferrous sulfate (325 mg) at 3 hours before or 2 hours after gemifloxacin showed negligible effects. The pharmacokinetics of gemifloxacin have not been studied in combination with the various didanosine formulations, but significant reductions in bioavailability have been reported for ciprofloxacin, another quinolone, in interaction studies with didanosine.

MANAGEMENT: Gemifloxacin should be administered at least 2 hours before or 3 hours after didanosine buffered tablets or pediatric oral solution, and patients should be monitored for potentially decreased antimicrobial efficacy during concomitant therapy. Didanosine buffered powder for oral solution, which uses a citrate-phosphate buffer, and the delayed-release capsules, which are not buffered, are not expected to cause this interaction.

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