Ciprofloxacin concentrations in human fluids and tissues following a single oral dose

Ciprofloxacin is a new quinolone carboxylic acid derivative which exerts its antibacterial activity at very low concentrations against a wide spectrum of microorganisms. Ciprofloxacin serum and urine concentrations were studied in 10 healthy volunteers after a single 250 and 500 mg oral dose. The concentration in ascitic fluid was determined in four male patients undergoing paracentesis after a single oral 250 mg dose (two patients) and 500 mg dose (two other patients). The penetration of ciprofloxacin into the human tonsils and turbinate bones was also determined in eight patients undergoing tonsillectomy or turbinectomy 3 h after a single oral 250 mg administration. Ciprofloxacin concentrations were determined by an agar diffusion test utilizing E. coli as reference strain. Ciprofloxacin is rapidly absorbed after oral administration (Ka = 2.67 and 1.93 mcg/ml) and its serum concentration does not vary significantly with sex and dosage (Cmax = 2.61 and 1.99 mcg/ml after a single 500 mg and 250 mg oral dose). Urinary concentrations of ciprofloxacin are twice higher after a single 500 mg dose than after a 250 mg one and are still high after 24 h (37.2 and 25.3 mcg/ml). The concentrations of ciprofloxacin in ascites, tonsils and turbinate bones are several times higher than its MICs against the majority of Gram+ and Gram- aerobic bacteria. The in vitro activity of ciprofloxacin and its human pharmacology suggest a twice daily 250 of 500 mg dosing for infections caused by multiple antibiotic-resistant bacteria, and a once a day dose in the treatment of urinary tract infections.