Intravenous administration of local anesthetics such as xylocaine has been widely used to determine the indication to use anticonvulsant for tinnitus or simply to relief tinnitus. Main drawback of this prescription is its side effects, such as cardiovascular depression. Since the effectiveness of the local anesthetic to tinnitus is attributed to its anticonvulsive effect, we thought intravenous administration of anticonvulsant itself might be effective for tinnitus and prepare more direct information about it. With the patient in sitting position, 250 mg of Phenytoin (also known as diphenylhydantoin, Aleviatine®) in 100 ml of saline was intravenously administrated in about 10 min. If the tinnitus disappeared, the administration was discontinued at that point. Fourty patients with tinnitus were submitted to the Aleviatine test. Thirty (75%) had a positive result, i. e. 60% or more reduction in the intensity of tinnitus. Within this group, 22 (55%) experienced complete relief (disappearance) of tinnitus for a while. Seven (17.5%) had a negative result, i. e. less than 40% improvement, and in 1 (2.5%) the tinnitus was worse following the Aleviatine injection. Major side effects, such as blackout sensation of eyes, flushing of face and numbness of extremities were observed in 3 (7.5%). The concentration of Aleveatine in serum drawn three minutes after the completion of injection was measured by homogenous enzyme immunoassay. The concentration ranged from 3.5 to 22 μg/ml. The positive relationship between serum concentration and administrated doses per body weight was observed. There was, however, no significant relationship between effectiveness and serum concentration of drug. In order to determine the site and mode of action of Aleviatine we have given it intravenously while recording the auditory brainstem response (ABR). None of patient showed any significant changes of ABR. In guinea pig, however, given more than 20 mg/Kg body weight of Aleviatine, a significant change of ABR was observed. Latency and amplitude of Pi as well as those of other peak was dosedependently prolonged. From these results site and mode of action was briefly discussed, especially in terms of biochemical neuropharmacology.(This research was supported by the Grant-in-Aid for Co-operative Research, No 56370028 from the Ministry of Education, Science and Culture of Japan.)
