Drug interactions with quinolones.

The mechanisms involved in drug interactions may be either pharmacokinetic or pharmacodynamic. Pharmacokinetic interactions are the leading events and are caused by alterations in absorption, distribution, metabolism, and elimination of one drug by another. The reported interactions of new quinolones are due to a decrease in antimicrobial activity at low pH, a Mg++-dependent reduction in efficacy, and a probenecid-induced decrease in tubular secretion of ciprofloxacin. The reduction of theophylline clearance by those quinolones that are metabolized primarily in the liver (enoxacin and ciprofloxacin) is of clinical relevance; also, the interactions of quinolones with Mg++-containing antacids, which result in tremendous loss of bioavailability, are of therapeutic importance.