Caffeine: Some quinolones, including ciprofloxacin, have also been shown to interfere with the metabolism of caffeine. This may lead to reduced clearance of caffeine and a prolongation of its serum half-life.

Cyclosporine: Some quinolones, including ciprofloxacin, have been associated with transient elevations in serum creatinine in patients receiving cyclosporine concomitantly.

Glyburide: The concomitant administration of ciprofloxacin with the sulfonylurea glyburide has, on rare occasions, resulted in severe hypoglycemia.

Histamine H2-receptor antagonists: Histamine H2-receptor antagonists appear to have no significant effect on the bioavailability of ciprofloxacin.

Methotrexate: Renal tubular transport of methotrexate may be inhibited by concomitant administration of ciprofloxacin, potentially leading to increased plasma levels of methotrexate. This might increase the risk of methotrexate toxic reactions. Therefore, patients under methotrexate therapy should be carefully monitored when concomitant ciprofloxacin therapy is indicated.

Multivalent cation-containing products: Concurrent administration of a quinolone, including ciprofloxacin, with multivalent cation-containing products such as magnesium or aluminum antacids, sucralfate, VIDEX® chewable/buffered tablets or pediatric powder, or products containing calcium, iron, or zinc may substantially decrease the absorption of ciprofloxacin, resulting in serum and urine levels considerably lower than desired. Proquin XR should be administered at least 4 hours before or 2 hours after these products. This time window is different than for other oral formulations of ciprofloxacin, which are usually administered 2 hours before or 6 hours after antacids. (See CLINICAL PHARMACOLOGY: Drug Interactions, PRECAUTIONS: Information for Patients, and DOSAGE AND ADMINISTRATION)

Non-steroidal anti-inflammatory drugs (but not aspirin): These drugs in combination with very high doses of quinolones have been shown to provoke convulsions in pre-clinical studies.

Omeprazole: The rate and extent of absorption of ciprofloxacin was bioequivalent when Proquin XR was given alone or when Proquin XR was given 2 hours after omeprazole at the dose that maximally suppresses gastric acid secretion. Omeprazole should be taken as directed and Proquin XR should be taken with a main meal of the day, preferably the evening meal. (See CLINICAL PHARMACOLOGY: Drug Interactions and Information for Patients).

Phenytoin: Altered serum levels of phenytoin (increased and decreased) have been reported in patients receiving concomitant ciprofloxacin.

Probenecid: Probenecid interferes with renal tubular secretion of ciprofloxacin and produces an increase in the level of ciprofloxacin in serum.

Theophylline: As with some other quinolones, concurrent administration of ciprofloxacin with theophylline may lead to elevated serum concentrations of theophylline and prolongation of its elimination half-life. This may result in increased risk of theophylline-related adverse reactions. (See WARNINGS) If concomitant use cannot be avoided, serum levels of theophylline should be monitored and dosage adjustments made as appropriate.

Warfarin: Quinolones have been reported to enhance the effects of the oral anticoagulant warfarin or its derivatives. When these products are administered concomitantly, prothrombin time or other suitable coagulation tests should be monitored.