Antacids: The interaction of Proquin XR (administered as a single 1000 mg [2 x 500 mg] dose) and magnesium/aluminum-containing antacids (900 mg aluminum hydroxide and 600 mg magnesium hydroxide administered as a single oral dose) was evaluated in healthy volunteers. When Proquin XR was given 2 hours after antacids and 6 hours before antacids, the Cmax values were similar to those when Proquin XR was given alone and AUC values were reduced by approximately 10%. When Proquin XR was given 4 hours before antacids, Cmax was reduced by approximately 11% and AUC was reduced by approximately 22%. Thus, to minimize the effect of antacids on the absorption of ciprofloxacin, Proquin XR should be given either 2 hours after or at least 4 hours before antacids (see PRECAUTIONS: Drug Interactions, and Information for Patients).

Caffeine: Some quinolones, including ciprofloxacin also decrease caffeine clearance and inhibit the formation of paraxanthine after caffeine administration. (See PRECAUTIONS: Drug Interactions)

Calcium-containing beverages: Concomitant administration of ciprofloxacin with milk products or calcium-fortified juices alone should be avoided since decreased absorption is possible. (See PRECAUTIONS: Drug Interactions and Information for Patients, and DOSAGE AND ADMINISTRATION)

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

Metronidazole: The serum concentrations of ciprofloxacin and metronidazole were not altered when these two drugs were given concomitantly.

Multivalent cation-containing products: Concomitant administration of ciprofloxacin with sucralfate, VIDEX® (didanosine) chewable/buffered tablets, metal cations such as iron and calcium, and multivitamin preparations with zinc should be avoided. (See PRECAUTIONS: Drug Interactions and Information for Patients)

Omeprazole: When Proquin XR was administered following a meal as a single 1000 mg dose (2 x 500 mg), 2 hours after the third dose of omeprazole (given 40 mg once daily for three days) to 27 healthy volunteers, the mean AUC and Cmax of ciprofloxacin were bioequivalent to the mean AUC and Cmax values when Proquin XR was administered alone. Omeprazole should be taken as directed and Proquin XR should be taken with a main meal of the day, preferably the evening meal. (See PRECAUTIONS: Drug Interactions and Information for Patients)

Probenecid: Co-administration of probenecid with fluoroquinolones results in a reduction in the renal clearance and an increase in their concentrations in the systemic circulation.

Theophylline: Previous studies with quinolones, including ciprofloxacin, have shown that concomitant administration of these drugs with theophylline decreases the clearance of theophylline resulting in elevated serum theophylline levels and increased risk of a patient developing central nervous system (CNS) or other adverse reactions. (See WARNINGS, PRECAUTIONS: Drug Interactions)

Warfarin: Ciprofloxacin and other 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 closely monitored. The co-administration of single doses of Proquin XR and Coumadin® (7.5 mg) did not result in significant changes in the pharmacokinetics of ciprofloxacin nor did it significantly affect the pharmacodynamics of S-warfarin and R-warfarin. Although the Cmax and AUC of the two warfarin enantiomers and the elimination half-life of S-warfarin were not significantly altered by ciprofloxacin co-administration, the half-life of R-warfarin was statistically significantly prolonged (P=0.029). (See PRECAUTIONS: Drug Interactions)