Drug Interaction Report

ADJUST DOSING INTERVAL: The oral bioavailability of cefdinir may be significantly decreased by concomitant administration of iron preparations. The proposed mechanism is chelation of cefdinir by the iron cation, forming a complex that is poorly absorbed from the gastrointestinal tract. According to the product labeling, coadministration of cefdinir with a therapeutic iron supplement containing 60 mg of elemental iron (as ferrous sulfate) or vitamins supplemented with 10 mg of elemental iron resulted in a reduction of cefdinir absorption by 80% and 31%, respectively. In a study of six healthy volunteers, simultaneous administration of cefdinir (200 mg single oral dose) with a sustained-release formulation of ferrous sulfate (1050 mg, equivalent to 210 mg elemental iron) led to greater than 90% decreases in mean cefdinir peak plasma concentration (Cmax) and systemic exposure (AUC) compared to administration of cefdinir alone. Even when the iron preparation was administered 3 hours after cefdinir, cefdinir Cmax was still reduced by 25% and AUC by 36%.

MANAGEMENT: To minimize potential interaction with iron, the product labeling recommends that cefdinir be taken at least 2 hours before or 2 hours after administration of iron-containing products. However, this separation time may not be sufficient to prevent the interaction when sustained-release iron products are used, especially in higher dosages. Patients should be advised that reddish stools may occur due to formation of a nonabsorbable complex between cefdinir or its breakdown products and iron in the gastrointestinal tract.

ADJUST DOSING INTERVAL: Concomitant use of some oral medications may reduce the bioavailability of orally administered iron, and vice versa.

Food taken in conjunction with oral iron supplements may reduce the bioavailability of the iron. However, in many patients intolerable gastrointestinal side effects occur necessitating administration with food.

MANAGEMENT: Ideally, iron products should be taken on an empty stomach (i.e., at least 1 hour before or 2 hours after meals), but if this is not possible, administer with meals and monitor the patient more closely for a subtherapeutic effect. Some studies suggest administration of iron with ascorbic acid may enhance bioavailability. In addition, administration of oral iron products and some oral medications should be separated whenever the bioavailability of either agent may be decreased. Consult the product labeling for specific separation times and monitor clinical responses as appropriate.