OBJECTIVETo determine pharmacokinetics profiles of methylprednisolone (MTH) in perilymph and plasma of guinea pig after intratympanic injection of MTH in different concentrations.

METHODSBy auripuncture, three different concentrations of MTH were used in guinea pigs: 32.0 mg/ml, 40.0mg/ml and 62.5 mg/ml. Samples of plasma and perilymph of the scala tympani were collected at 1-12 h after administration and the concentrations of MTH were assayed using high-performance liquid chromatography. Auditory brainstem response (ABR) was detected before and 12h after MTH administration.

RESULTSThe concentrations of MTH in perilymph were dose-related. The differences of MTH concentrations in perilymph before and at series sampling time after administration were significant in statistics (P < 0.05), except for the intervals of 5 h, 6 h and 12 h. In addition, the concentration of MTH in perilymph was the highest in 62.5 mg/ml group. No MTH was detected in plasma after local administration, except for 1.5 h and 2 h after administration with 62.5 mg/ml. There were not differences in the thresholds of wave III of ABR before and 12h after local MTH administration among three groups (P > 0.05).

CONCLUSIONSThe experimental results indicates that the concentration of 62.5 mg/ml of MTH is optimal for treatment inner ear diseases by intratympanic administration among three groups, it get a high concentration in perilymph and not effect on the function of inner ear.