ENZYME-IMMUNOASSAY OF GENTAMICIN WITH USE OF A CENTRIFUGAL ANALYZER

Gentamicin was determined in [human] serum by the homogeneous enzyme immunoassay system (EMIT) adapted to the Multistat centrifugal analyzer. The standard curve can be extended to 16 mg/L; poor precision is obtained at concentrations > 10 mg/l because a small difference in change in absorbance there produces a significant variation in gentamicin concentration. The within-run precision of the method (CV) was 3.4% for a 5.0 mg/l sample (range 4.6-5.4 mg/l and 11.1% for a 12.2 mg/l sample (range 10.4-15.4 mg/l. All samples containing gentamicin at concentrations exceeding 10 mg/l should be diluted with Tris buffer. Recovery of gentamicin added to 4 serum specimens averaged 102%. There is no interference from bilirubin at concentrations up to 200 mg/l or from moderately lipemic samples. Hb in serum in excess of 625 mg/l results in lower gentamicin values. Gentamicin is stable for 6 days in serum stored at 23, 4 or -20.degree. C. Comparison of gentamicin results by the proposed method with those by a manual EMIT procedure, and with those by a homogeneous fluorescence immunoassay method gave correlation coefficients of 0.986 and 0.947.