Drug Interactions between Videx and Zagam Respipac

ADJUST DOSING INTERVAL: Concomitant administration with didanosine buffered tablets or pediatric oral solution may reduce the oral bioavailability of sparfloxacin 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. In 20 healthy volunteers, administration of an antacid containing aluminum and magnesium hydroxide (Maalox 30 mL) 2 hours before and 2 hours after a single 400 mg dose of sparfloxacin reduced the mean peak plasma concentration (Cmax) of sparfloxacin by 29% and 13% and its area under the concentration-time curve (AUC) by 23% and 17%, respectively. Administration of the antacid 4 hours after sparfloxacin showed no significant effect. The pharmacokinetics of sparfloxacin 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. There is some evidence, however, that chelation of sparfloxacin by divalent and trivalent cations is less marked than with ciprofloxacin, enoxacin, or norfloxacin.

MANAGEMENT: Sparfloxacin should be administered at least 4 hours before 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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