Interactions Reducing Absorption

Metallic cations significantly reduce oral absorption of fluoroquinolones by chelation in the gut. Coadministration of antacids—notably combinations of aluminum and magnesium hydroxide (Maalox)—from 2 hours before to 6 hours after dosing consistently reduces bioavailability by 30-90%. Sucralfate has similar effects. Such combinations may result in therapeutic failure [109]. Oral iron and, to a lesser extent, multivitamin-zinc complexes reduce quinolone bioavailability [110].

Although most such interactions are clinically inapparent, a study of hospital inpatients suggested that up a third receiving ciprofloxacin also received agents known to chelate the drug in the gut [111]. The possibility of therapeutic failure due to impaired absorption is clearly possible, and education of prescribers is necessary.

Coadministration of fluoroquinolones with food does not significantly reduce absorption although Cmax values are decreased. H2 antagonists do not affect absorption except with enoxacin, for which bioavailability is decreased by 40%, but agents with effects on gastric motility (e.g., pirenzepine) may prolong the absorption phase [109].

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