Ototoxic potential of gentamicin in ponies

Ototoxicosis was evaluated in 6 healthy ponies given 5 mg of gentamicin/kg of body weight, q 8 h, IM. Ponies 1, 2, and 3 were dosed for 7 days and ponies 4, 5, and 6 were dosed for 14 days. Serum peak and trough concentrations of gentamicin were measured by radioimmunoassay at regular intervals. Brain stem auditory-evoked responses were recorded every 5 days up to 60 days after the first dose to monitor auditory function. Although serum gentamicin concentrations were within or above the accepted clinical therapeutic range, loss of auditory function was not observed at the frequency range (1 to 4 kHz) tested. Serum chemical values remained within the accepted clinical range and no evidence of nephrotoxicosis was observed. Seemingly, gentamicin given IM to healthy ponies was safe and had minimal risk of side effects.