Predictability of blood levels of gentamicin in man

Data from 42 patients were analyzed to determine the predictability of the peak serum level and the t1/2 of gentamicin on the bases of age, sex, body weight, serum concentration of creatinine, and blood hematocrit. Renal function was normal in 21 patients and impaired in 21. The most striking finding was the relatively poor predictability of t1/2 of gentamicin from serum concentration of creatinine. The overall correlation coefficient was 0.749 (P less than 0.001) in contrast to values of greater than 0.9 reported by others. tthere was a significant correlation of the t1/2 of gentamicin with the reciprocal of hematocrit (r * 0.647, P less than 0.001). Linear regression equations taking account of sex, serum creatinine concentration, and reciprocal of hematocrit provided a somewhat higher correlation coefficient (0.821) with the t1/2 of gentamicin than did the equation including serum creatinine concentration alone but were still not fully satisfactory. Thus the pharmacokinetics of gentamicin may not be adequately predictable from standardized equations or nomograms.