Assay of gentamicin concentrations in serum specimens by microbiological and radioenzymatic methods

Assay of gentamicin concentrations were performed on 167 patient sera by two methods in the routine work. A radioenzymatic method that measures the acetylation of getamicin by a bacterial enzyme extract and the overnight agar diffusion method, using cups as diffusion centres, were used. The methods correlated well (r = 0.87), although the results of the microbiological assay in some cases were higher than the results of the enzymatic assay. When artificial samples were tested the microbiological methods gave variable results. Therefore careful standardization is necessary for accuracy and reproducibility. The enzymatic assay, however, offered advantages of specificity, reproducibility and rapidity.