Increased aminoglycoside dosage requirements in hematologic malignancy

Aminoglycoside pharmacokinetic parameters were studied prospectively in 27 patients with an underlying hematologic malignancy and fever associated with neutropenia and in 18 control patients. Pharmacokinetic parameters and dosages were determined by linear regression analysis of a one-compartment model by the method of Sawchuk et al. (R. J. Sawchuk, D. E. Zaske, R. J. Cippolle, W. A. Wargin, and R. G. Strate, Clin. Pharmacol. Ther. 21:362-369, 1976). Significant differences between the study and control groups were found for aminoglycoside volume of distribution (0.40 +/- 0.1 versus 0.27 +/- 0.05 liter/kg [mean +/- standard deviation], respectively; P less than 0.0001), clearance (116.6 +/- 48.9 versus 68.6 +/- 26.7 ml/min, respectively; P less than 0.0001), half-life (2.27 +/- 0.66 versus 3.5 +/- 1.8 h, respectively; P less than 0.0001), and elimination rate constant (0.33 +/- 0.11 versus 0.24 +/- 0.09 h-1, respectively; P less than 0.001). The percentage of bone marrow blast cells (at the time of diagnosis) in patients with acute leukemia significantly correlated with increased aminoglycoside clearance (R2 = 36.98%; P = 0.0001). Patients with stage IV lymphomas (Hodgkins disease and non-Hodgkins lymphoma) had a significantly increased clearance compared with patients with lower stages of lymphomas (105.1 +/- 18.5 versus 84.1 +/- 14.9 ml/min; P = 0.014). Fever, leukocyte count, or chemotherapy, among other clinical and laboratory parameters that were studied, had no significant correlation or effect on aminoglycoside disposition. The average dose of amikacin required to maintain peak concentrations in serum above 20 micrograms/ml in patients with a hematologic malignancy was 27.5 +/- 8.43 mg/kg per day. Pharmacokinetic parameters and dosages for the control patients were comparable to general literature standards. we conclude that the dosages recommended by the manufacturers or those derived from nomograms underestimate the aminoglycoside volume of distribution and clearance in patients with a hematologic malignancy and result in suboptimal peak aminoglycoside concentrations in serum. We recommend that in febrile neutropenic patients with an underlying hematologic malignancy, amikacin be initiated at 7.5 to 10 mg/kg per dose every 8 h (2 to 2.5 mg/kg per dose every 8 h for gentamicin) and adjusted within 24 h based on individual pharmacokinetic analysis.