125I-Radioimmunoassay of amikacin and comparison with a microbioassay

A radioimmunoassay (RIA) has been developed using 125I-amikacin. Amikacin was iodinated by a modified BOLTON and HUNTER method. Dextran-charcoal was used to separate bound from free drug. The standard curve was linear on a logit-log plot in the range of 0.5 ng to 4 ng amikacin per tube. There was no cross-reactivity of amikacin antisera to the amino-glycosides gentamicin, tobramycin, netilmicin, and sisomicin but a 70% cross-reaction was observed with kanamycin, the compound from which amikacin is synthetically derived. Correlation of the RIA with a microbioassay for the determination of serum amikacin levels in 18 patient samples was excellent (r = 0.94). This new RIA technique is more sensitive, rapid, versatile, and less costly than the RIA using 3H-amikacin, and is far more sensitive and faster than microbioassay.