Methylcobalamin as antagonist to transient ototoxic action of gentamicin

The objective of this study was to determine whether methylcobalamin inhibi ts the ototoxic action of gentamicin. Fourteen pigmented guinea pigs were r andomly divided into experimental and control groups. Each animal in the ex perimental group was given a large single dose of gentamicin (125 mg/kg i.m .), followed by immediate administration of methylcobalamin (1 mg kg i.m.). In the control group, the animals received gentamicin only, at the same do se as the experimental group. The compound action potentials (CAPs) in the right ears of animals were measured using a signal processor before and 15, 30, 45, 60 and 75 min after injection of the drugs. The sound stimulus was presented by means of clicks and tone pips at 2, 4 and 8 kHz. Following th e electro-physiological tests, the animal was sacrificed and prepared for s canning electron microscopic observation. There was prolongation of latency and diminution of amplitude of CAPs N-1 and N-2 15 min after injection of gentamicin. Although the N-1-N-2 intervals increased as the time after inje ction of gentamicin increased, the variations were still within normal rang es. In contrast, there was no prolongation of N-1 latencies or N-1-N-2 inte rvals 30 min after injection in the experimental group. There were no marke d changes in N-1 or N-2 amplitudes, compared with the results before inject ion, in the experimental group. The firing mechanism of the inner ear may b e affected by a single dose of gentamicin. This suggests that the transient ototoxic action of gentamicin hardly affected the conductive function of t he nerve fibres, even though the firing function of the inner ear was influ enced. Methylcobalamin may inhibit the ototoxic side effects of gentamicin.