Urinary concentrations of fosfomycin after a single 3 g dose of fosfomycin to elderly nursing-home patients.

The urinary concentrations of fosfomycin in 7 elderly patients with impaired renal function (mean creatinine clearance 40 ml/min) were studied after a single oral dose of 3 g fosfomycin as the trometamol salt. Urine samples were collected as 12 h portions for 84 h. Urinary concentrations of fosfomycin were 1,383 mg/l (range 314 to 4,200 mg/l) in the first 12 h and gradually declined to 165 mg/l (range 65 to 365 mg/l) between 36 and 48 h. 37% of the oral dose was recovered in the urine unchanged after 84 h, but a wide range (15-60%) in urinary recovery was observed. The elimination half-lives in the patients (estimated from the renal excretion profile of fosfomycin) ranged between 7 and 24 h. These data suggest that the urinary levels obtained in this patient population exceed the minimum inhibiting concentration of the usual pathogens involved in uncomplicated cystitis for at least 48 h. After 24 h the urinary concentrations of fosfomycin are higher than those reported for healthy young subjects.