Pharmacokinetics of the Aminoglycoside Antibiotic Tobramycin in Humans

The pharmacokinetics, distribution, and plasma and renal clearance of a new aminoglycoside antibiotic, tobramycin, was studied in the treatment of 18 elderly male patients (average age, 69 years) with urinary tract infections. Ten of these patients had normal renal function and eight had impaired renal function of various degrees. After administration of 1 mg of tobramycin/kg of body weight every 6 to 8 h (two to three times the half-life), urine concentrations were found to be sufficient in the treatment of urinary tract infections caused by susceptible organisms. The renal clearance of tobramycin during constant intravenous infusion was also studied in eight patients. Good correlation was found between the patients serum creatinine and the half-life of tobramycin. The half-life of tobramycin in patients with normal renal function (serum creatine [Formula: see text] to 1.5 mg/100) was on the average 3 h. For practical purposes, therefore, the dosage of tobramycin in the treatment of urinary tract infections should be 1 mg/kg of body weight every 6 to 8 h in patients with normal renal function. For patients with impaired renal function, the dosage interval is calculated by multiplying the patients' serum creatinine by six. If the dosage intervals are kept unchanged, the dosage must be divided by the patients' serum creatinine. The initial loading dose should always be 1 mg/kg. The total renal clearance of tobramycin (92% of the glomerular filtration rate) was not influenced by the administration of probenecid, which indicates that tobramycin is excreted only by glomerular filtration.