Drug interactions of ciprofloxacin with other non-antibiotic agents.

Interactions between ciprofloxacin and other non-antibiotic agents occur; some can be predicted from in vitro results and general pharmacodynamic rules, whereas other interactions appear to be unpredictable. In the absorptive phase, neither food nor ranitidine, a histamine (H2)-receptor blocker, alters the absorption of ciprofloxacin. Pirenzipine, a cholinergic agent, and N-butyl-scopolaminium bromide delay the absorption of ciprofloxacin, whereas metclopramide accelerates absorption. Both magnesium- and aluminum-containing antacids significantly decrease the absorption of ciprofloxacin, probably through formation of a chelate complex. Patients receiving ciprofloxacin and theophylline simultaneously have higher serum theophylline levels than do recipients of theophylline alone. The interaction is probably due to the inhibition by ciprofloxacin of hepatic microsomal enzymes that metabolize theophylline. Ciprofloxacin does not displace bilirubin from albumin; thus, interactions resulting from displacement of highly protein-bound agents by ciprofloxacin are unlikely. Ciprofloxacin and other quinolones inhibit gamma-aminobutyric acid receptors through reduction of their binding capacity and thus may potentiate convulsions induced by other agents. Cimetidine, a cytochrome P450 antagonist, affects metabolizable quinolones, and it is likely that it may affect ciprofloxacin's disposition after prolonged use. Currently, the only clinically significant interactions are the inactivation of ciprofloxacin by antacids and an increase in theophylline blood levels in the presence of ciprofloxacin. In the future, attention should be paid to other possible interactions.