Analysis of serum for gentamicin by radioimmunoassay

A radioimmunoassay method for the determination of combined gentamicin isomers in serum has been adapted and tested. The procedure uses tritiated gentamicin, rabbit antiserum against a gentamicin-human albumin conjugate, and dextran-charcoal separation. The day-to-day coefficient of variation is 6 percent, and frozen samples are stable for at least one month. There was no cross reactivity of the antiserum with any of several tested antibiotics or with any of some tested commonly used non-antibiotic hospital pharmacy preparations. The results from the procedure correlated well with those of an enzymatic radioacetylation technique and, except for a significant incidence of "outliers", with a microbiological assay. As expected, patient serum values, both maximum and minimum, showed no correlation with dose size.