The Effects of Betahistine and Dimenhydrinate on Caloric Test Parameters; Slow-Phase Velocity of Nystagmus

OBJECTIVE: The aim of this study is to determine the effects of betahistine and dimenhydrinate on the slow phase velocity. MATERIALS and METHODS: Forty patients with complaints of vertigo and dizziness volunteered to be included in the study. All patients who were included the study were treated at the other medical centers. The patients were divided into two Groups. Patients in the first Group were given betahistine 24 mg three times per day. During this treatment, caloric testing was performed, and the dose was increased to 48 mg three times a day due to ongoing complaints. The test was then repeated four weeks after using this higher dosage. Patients in the second Group had caloric testing while using and four weeks after stopping dimenhydrinate. RESULTS: The study Group was comprised of 40 patients; 20 patients (13 female, 7 male, 18-68 years, median age 46) in the betahistine Group and 20 patients (14 female, 6 male, 24-74 years, median age 44.5) in the dimenhydrinate Group. The average slow phase maximum velocity in the first Group of patients was 18 -/+ 8.2 and 21.1 -/+ 10.8 deg/s at 24 mg betahistine three times a day and 48 mg three times a day, respectively. In the second Group of patients, the average slow phase velocity was 13.4 -/+ 5.1 and 18.2 -/+ 7.5 deg/s during and after stopping the treatment of dimenhydrinate, respectively. The caloric test-induced slow-phase velocity was decreased with dimenhydrinate and increased with the higher dosage of betahistine. CONCLUSION: To our knowledge, this is the first study to demonstrate that betahistine increases caloric-induced slow-phase velocity in humans. Dimenhydrinate and betahistine should not be used together because of their opposite effects on the vestibular system. Dimenhydrinate can be used to treat acute episodes of vertigo, whereas betahistine should not be used during the episode but may be used in the period between the attacks to stimulate the vestibular system.