Measurements of serum gentamycin levels by rapid tests

Gentamicin is a very useful antimicrobial agent for the treatment of serious infections caused by gram-negative bacteria. However, it's low therapeutic index and potential ototoxic and nephrotoxic side effects necessitate frequent determinations of serum concentration to assist in maintaining therapeutic levels and avoiding toxic levels. Two bioassays and a latex agglutination inhibition card (LAIC) test were evaluated to determine gentamicin levels in nearly 100 patient sera. Results were compared with a radioimmunoassay (RIA). Two bioassays, the Bio-Monitor and the GentaSak, gave correlation coefficients of 0.987 and 0.982, respectively. The correlation coefficient for the LAIC test was 0.987. All three tests compared well with RIA in accurately detecting gentamicin levels in patients as well as simulated sera. The LAIC test, however, was more rapid, giving results within half an hour whereas bioassays required 6--8 hours for completion. The LAIC test was also found to be more economical. It provides a suitable alternative to RIA procedures in small laboratories and for performing 'stat' tests since batching is not necessary.