Comparison of enzyme immunoassay, radioimmunoassay, and microbiologic assay for amikacin in plasma.

An enzyme-multiplied immunoassay technique (EMIT), radioimmunoassay (RIA), and microbiologic assay (MBA) were compared as methods of measuring amikacin in human plasma. Accuracy of the three methods was assessed in plasma with amikacin added in concentrations of 2.5-50 micrograms/ml. Correlations between the assay methods were compared over a range of 0.5-50 micrograms/ml. Amikacin was also assayed in plasma to which had been added other drugs, including 16 antibiotics and 3 antineoplastic agents; also tested were samples that had been stored at 5 degrees C or -20 degrees C. Within the amikacin concentration range of 2.5-50 micrograms/ml, the coefficients of variation of all methods were within 10%. Correlation was good between EMIT and RIA as well as between EMIT and MBA. Of the other drugs tested, only tobramycin, dibekacin, and kanamycin affected amikacin EMIT determinations, while only kanamycin affected amikacin RIA determinations. No effect of cold and freezing was observed on amikacin determinations. EMIT assay is an acceptable method for routine analysis of amikacin plasma samples. The amikacin assay results for the three methods were highly correlated.