Radioimmunoassay of tobramycin compared to microbial methods

A commercial radioimmunoassay (RIA) for tobramycin was compared with microbial methods by determining the concentrations of known standards prepared with pooled human serum. The correlation coefficients were r=0.94 for the RIA method and an agar diffusion procedure using commercial paper disk standard, and r=o.95 for a standard agar well diffusion procedure. The agar well method tended to overestimate the real concentrations.