Predictability of serum gentamicin concentrations in renal failure

To assess the problem of maintaining blood concentrations of gentamicin at therapeutically adequate levels while avoiding toxic levels, serum concentrations were determined by radioimmunoassay on 133 occasions in 18 patients who received a total of 22 courses of therapy. Creatinine clearances (C(cr)) ranged from 6 to 65 ml/min; the mean duration of therapy was nine days. A linear relationship was found between the ratio of actual dose to dose calculated by the Chan nomogram and the mean serum levels for both peak and trough values. An inverse relationship was found between mean trough levels and C(cr) values, but peak values did no correlate significantly with C(cr). No evidence of nephrotoxicity was seen, but transient ototoxicity occurred in one patient. Although serum gentamicin levels are reasonably predictable in patients with impaired renal function, they should be monitored at least twice weekly throughout the course of therapy.