[Evaluation of ototoxic effect of micronomicin by intravenous drip infusion].

Ototoxic effect of micronomicin (MCR) in intravenous drip administration was investigated in guinea pigs (300--400 g) receiving MCR for 30 days at dose of 50 and 100 mg/kg, respectively. MCR was dissolved in physiologic saline and 1.5 ml of the solution was infused through polyethylene tube into the left external jugular vein with Perista mini-pump for 60 minutes every day after measurement of body weight. Auditory impairment was monitored by pinna reflex audiometry. Pinna reflex loss was not detected in any animal in frequency range (0.5 to 20 kHz). Cochlear hair cell damage generally was of mild degree. Two out of 6 animals treated with MCR 50 mg/kg (Table 1) showed outer hair cell loss confined to unilateral basal end and posterior 3/4 of the first turn, respectively. Outer hair cell loss was noticed in 4 of 9 animals receiving MCR 100 mg/kg (Table 2); much less extensive in 3 animals, unsymmetrical slightly extensive in remaining 1. Unilateral circumscribed loss of inner hair cells was noticed at lower part of the hook in the latter one. Vestibular hair cell loss was scattered and less extensive and occurred in 4 of the 6 50 mg/kg given animals and in 7 of the 9 100 mg/kg ones. Comparison in incidence and extension of the outer hair cell loss of the cochlea (Tables 3, 4) in the present study and previous ones on the ototoxic effect of MCR in intramuscular and intravenous administration suggests that there was no distinct difference in enhancement of the ototoxic effect in the intravenous drip administration.