Drug Interactions between gatifloxacin and lanthanum carbonate

GENERALLY AVOID: Lanthanum carbonate should be administered with food for therapeutic efficacy. However, it is insoluble in water (<0.01 mg/mL at pH 7.5) and therefore cannot be dissolved in liquid for administration through an enteral feeding tube, because it may result in blockage of the tube.

MANAGEMENT: Administration of lanthanum carbonate with enteral feedings is not recommended. Alternative medications such as calcium carbonate suspension should be considered.

Concurrent ingestion of calcium-fortified foods (i.e., cereal, orange juice) may alter the bioavailability of gatifloxacin. The mechanism is chelation of calcium and the quinolone, resulting in decreased bioavailability. In the case of orange juice, inhibition of intestinal transport mechanisms (P-glycoprotein or organic anion-transporting polypeptides) by flavones may also be involved. Data have been conflicting: One study has reported no effect with milk coadministration. Another study reported a modest decrease in gatifloxacin bioavailability (13.5% decrease in Cmax,12% decrease in AUC, 15% increase in total clearance) when taken with 12 ounces of calcium-fortified orange juice instead of water, which could be clinically significant if the infecting organisms have borderline susceptibilities. The manufacturer states that gatifloxacin may be taken without regard to food, milk, or calcium. Clinicians should be aware of the possibility of an interaction if subtherapeutic effects are observed.