INSENSITIVITY OF THE CHICKEN-EMBRYO TO THE OTOTOXICITY OF AMINOGLYCOSIDE ANTIBIOTICS AND A LOOP DIURETIC

Guinea pigs are routinely used in the histological evaluation of the c ochlea as a method of testing for ototoxicity, but the procedures are very time-consuming. Because the avian cochlea is easier to examine an d newly hatched chicks are sensitive to the ototoxic effects of gentam icin, birds may be useful in testing for ototoxicity. The use of chick en embryos would be even better for testing, but whether or not chicke n embryos are sensitive to ototoxicants is unknown. In an attempt to d etermine whether or not chicken embryos may be used instead of guinea pigs in screening tests for ototoxicity, aminoglycoside antibiotics an d a loop diuretic, ethacrynic acid, were administered to chicken embry os. A maximum-tolerated dose of gentamicin, kanamycin, streptomycin, e thacrynic acid, or a combination of gentamicin and ethacrynic acid was administered to fertile eggs of White Leghorn chickens on incubation days 10-17. To compare the effect of route of exposure on ototoxicity, gentamicin was administered by injection into the allantoic space, yo lk sac, and air cell as well as by submerging the egg in gentamicin so lution. With the preferred air cell route the effects of the ototoxic drugs kanamycin, streptomycin, ethacrynic acid, and a combination of e thacrynic acid and gentamicin were compared. On incubation day 18, coc hleas were removed from the chicken embryos. Serial sections of these avian cochleas were examined and hair cells were counted. No significa nt difference was seen between the number of hair cells in cochleas of control chicken embryos and those from chicken embryos treated with d rugs. Therefore, the chicken embryo appears to be insensitive to the o totoxicity of aminoglycoside antibiotics and a loop diuretic.