Ototoxicity of 12 mg/kg cisplatin in the Fischer 344/NHsd rat using multiple dosing strategies.

Ototoxicity continues to be a major dose-limiting side effect of cis-diamminedichloroplatinum(II) (cisplatin). With an ongoing need to develop pharmaceutical protection strategies for cisplatin's ototoxicity, there is also a need to develop stable in-vivo mammalian models of cisplatin ototoxicity. The current study examined the difference in ototoxicity of a cumulative 12 mg/kg dose of cisplatin in the Fischer 344/NHsd rat when administered over four different dosing protocols. Hearing sensitivity was measured using free-field auditory brainstem response thresholds under anesthesia. Rats were divided into four groups. The first group was administered 12 mg/kg of cisplatin in a single bolus infusion. The second group was administered two 6 mg/kg infusions separated by 7 days. The third group was administered 3 mg/kg injections once per day for 4 consecutive days. The fourth group was administered 3 mg/kg injections in four injections separated by 3 days each. Hearing thresholds and body weights were measured at 3 and 7 days after the final cisplatin exposure. Postmortem sensory cell counts were used to confirm injury to the auditory system. The 4 consecutive days of 3 mg/kg induced a greater mortality rate and greater hearing loss at day 3 than the other experimental protocols. The 3 mg/kg administered every 3 days induced less sensory cell loss than the other conditions. The findings indicate that 4 consecutive days of 3 mg/kg cisplatin is not a viable ototoxicity model in the Fischer 344/NHsd rat, but that the other models are all effective in inducing comparable cochlear injuries.