Comparison of standard versus pharmacokinetically adjusted amikacin dosing in granulocytopenic cancer patients

The capabilities of two pharmacokinetic amikacin dosing methods were evaluated and compared with the standard amikacin dosage recommended by the manufacturer. Study patients participated in two consecutive prospective randomized double-blind trials of empiric antibiotic therapy for febrile episodes during granulocytopenia. Patients in study 1 received amikacin at a dosage of 15 mg/kg per day in four divided doses in combination with either ticarcillin or piperacillin. Patients in study 2 received either ticarcillin or moxalactam in combination with amikacin. Amikacin dosages in study 2 were adjusted to achieve a 1-h-postinfusion concentration of approximately 25 micrograms/ml and a trough concentration of approximately 8 micrograms/ml. Initial amikacin dosage requirements were established based on the lean body weight and estimated renal function of the patient. If amikacin serum concentrations were not within acceptable ranges, further dosage adjustments were made by using patient-specific pharmacokinetic parameters. The median 1-h-postinfusion concentration of amikacin in study 1 was 13.0 micrograms/ml, with a median trough concentration of 6.1 micrograms/ml. In study 2 the median 1-h-postinfusion concentration was 20.8 micrograms/ml, with a median trough of 6.4 micrograms/ml. Patients in study 2 required a mean dosage of 29.4 mg/kg per day. The incidence of amikacin-induced nephrotoxicity was not increased despite the substantial increase in dosage. Ototoxicity was not evaluated in study 1, but the incidence of ototoxicity in study 2 (17%) exceeded the incidence observed in a previous amikacin-plus-ticarcillin trial in which patients received 15 mg of amikacin per kg per day.