Drug Interactions between Omnicef Omni-Pac and Vitatab MV

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.

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