Impact of aminoglycoside serum assays on clinical decisions and renal toxicity

To determine whether serum aminoglycoside assays aided clinicians in treating infections and avoiding aminoglycoside nephrotoxicity, we reviewed the charts of patients treated with aminoglycoside antibiotics parenterally. We compared 78 episodes of aminoglycoside-treated infections during which serum assays were done (group B) to 51 episodes without serum assays (group A). The groups of patients were comparable in age, outcome of infection, incidence of aminoglycoside nephrotoxicity, mean total dose of aminoglycosides given, and number of courses. Toxic trough levels of tobramycin (the most frequently used aminoglycoside) were seldom detected before the onset of nephrotoxicity, and peak tobramycin levels were frequently suboptimal. While 71% of decisions to increase or decrease the aminoglycoside dose after serum assays were considered appropriate, only 57% of noninterventions were appropriate. At our hospital, serum aminoglycoside assays did not help improve the outcome of infection or the incidence of nephrotoxicity. Their major clinical contribution was to alert the physician that serum concentrations were low.