A Safety/Efficacy Trial of Zonisamide for Essential Tremor

Essential tremor is common, affecting about four percent of the population above age 40 years. Of these, about half have troublesome tremor that warrants medical therapy, but only half of these find satisfactory treatment. Thus it can be estimated that about one million Americans have not been able to find adequate therapy for their essential tremor. Presently used medications may fail due to lack of efficacy or tolerance. After encountering anecdotal experience of zonisamide's efficacy for essential tremor we decided to conduct a single-site open-treatment rising-dose study with blinded videotape ratings of tremor. Zonisamide is presently on the market in the United States for epilepsy. Its use in other conditions is experimental.

Healthy participants with bilateral hand tremor will initially sign an IRB-approved informed consent form, then have assessments in a Screening Visit to determine that they are healthy (physical and neurological examinations, routine blood tests, electrocardiogram) and tremor assessments with rating scales. Tremor at each visit will be videotaped, as well as assessed openly by a rater. If participants meet eligibility criteria, they will return to a Baseline Visit (Visit 1) for repeat tremor assessment and the initial dispensation of zonisamide.

The study drug initially will taken as one 50-mg tablet a day, then the dose increased by one tablet each two weeks, to no more than 3 tablets (150 mg) taken twice a day. During this 12-week dose adjustment phase, the participant will be seen in clinic each 4 weeks for tremor assessments and review of health status. In addition, the participant will be contacted by telephone each week. If any symptom occurs suggestive of side effects, the escalation will be stopped or the dose reduced in order to resolve the symptom.

At the end of the 12-week dose adjustment phase, at Visit 4, it will be determined whether meaningful tremor reduction has occurred at the target dose of 300 mg per day or at a lesser but tolerated dose. If not, the participant will discontinue from the study. If benefit has occurred, the subject will be invited to continue taking zonisamide for another 12 weeks, at the conclusion of which the participant will be seen in the final visit (Visit 5).

The videotapes will be coded so that the order they were made is not apparent, and the degree of tremor will be rated by a rater who does not know the study participants.