Absorption

When Proquin XR is administered with food, approximately 87% of ciprofloxacin is gradually released from the tablet over a 6-hour period. When administered following a meal maximum plasma ciprofloxacin concentrations are attained approximately 4.5-7 hours after dosing with Proquin XR tablets. Proquin XR should be administered with a main meal of the day, preferably the evening meal; if Proquin XR is given while fasting, the bioavailability will be lowered substantially. Administration of Proquin XR with a standardized meal (1000 calories, 50% fat) increased the Cmax and AUC_0-24h by approximately 120% and 170%, respectively, compared to administration under fasting conditions; the mean Tmax was prolonged from 2.3 hours to 4.5 hours. The following table presents the pharmacokinetic parameters obtained at steady state for Proquin XR 500 mg qd versus CIPRO 250 mg bid.

Steady-State Pharmacokinetics for Ciprofloxacin in Plasma of Healthy Subjects (Day 3)^a

Distribution

The in vitro binding of ciprofloxacin to plasma proteins over a concentration ranging from 0.9 to 30 micromolar is 9.9% to 36.6%, which is not likely to cause clinically significant protein binding interactions with other drugs.

Metabolism

Four metabolites of ciprofloxacin have been identified in human urine and feces. The metabolites have antimicrobial activity, but are less active than unchanged ciprofloxacin. The metabolites are desethyleneciprofloxacin (M1), sulfociprofloxacin (M2), oxociprofloxacin (M3), and formylciprofloxacin (M4), which account for approximately 11% of the total dose.

Elimination

The plasma elimination half-life of ciprofloxacin in healthy volunteers following a Proquin XR 500 mg dose was approximately 4.5 hours. Following a 500 mg oral dose of Proquin XR, 26.9% was excreted in the urine over 24 hours as unchanged drug for both formulations.

Following administration of a single 500 mg dose of Proquin XR, approximately 41% of the oral dose was excreted into the urine over 96 hours as unchanged drug and metabolites. The urinary excretion of ciprofloxacin was virtually complete within 24 hours after dosing. Urinary excretion is a main route of elimination of ciprofloxacin and its urinary concentrations relative to the MICs of the bacterial species may be important to understanding the efficacy of ciprofloxacin for the treatment of urinary tract infections. The mean urinary ciprofloxacin concentration after dosing with Proquin XR 500 mg qd and CIPRO 250 mg bid are shown in the following table:

Mean Urinary Concentrations of Ciprofloxacin

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