Update on quinolone drug interactions.

Concurrent administration of both ciprofloxacin and norfloxacin with sucralfate leads to a decrease in quinolone bioavailability. It is unknown whether this decrease is clinically significant because studies have focused primarily on pharmacokinetics and not therapeutic outcomes. A reasonable recommendation may be to avoid using sucralfate and norfloxacin concurrently, or avoid administration of norfloxacin and ciprofloxacin within two hours of sucralfate administration. Magnesium- and aluminum-containing antacids may also interfere with quinolone absorption. Calcium carbonate and H2 receptor antagonists do not appear to interact with quinolones and may be considered as an alternative to sucralfate or magnesium- and aluminum-containing antacids when quinolones are administered. Concurrent administration of ciprofloxacin and theophylline may precipitate theophylline toxicity if not monitored carefully. Some clinicians recommend a 30% empiric reduction in theophylline dosage when ciprofloxacin therapy is initiated. Because the drug interaction is not completely predictable, the patient's theophylline levels should be monitored and signs and symptoms of toxicity noted, adjusting the dose as needed. Decreased theophylline clearance may persist for as long as five days following discontinuation of ciprofloxacin. Some potential for slight increases in serum theophylline concentrations secondary to norfloxacin administration may exist. However, it is unlikely to be clinically significant, based on currently available information.