Tobramycin therapy--two or three doses per day?

11 patients with moderate infections were treated with bolus injections of tobramycin in a fixed dose of 4.5 mg/kg and day for 8 days. The patients were randomized to injections every 8 h (TID) for 4 days followed by injection every 12 h (BID) or vice versa. Serum concentrations were measured on day 2 of each regimen. The TID regimen gave peak levels less than 4 micrograms/ml in 5/11 patients, mean value 4.2 micrograms/ml. With the BID regimen 2 patients had peaks less than 4 micrograms/ml, mean value 5.9 micrograms/ml. The BID regimen seems preferable when treating patients with normal renal function. The bolus injections were well tolerated.