Cerebellar tremor is a frequent and disabling symptom in multiple sclerosis (MS) patients. Supportive pharmacological treatment with different drugs showed only minor effects in a few studies and in clinical practice. Encouraged by previous studies with ondansetron, a 5HT3-antagonist, we conducted a small open-label, prospective and controlled study with 14 MS patients suffering predominantly from cerebellar tremor of the upper extremities. Principal outcome measure to evaluate a functional improvement of the single intravenous administered ondansetron injection was the subject performance in the 9-hole-peg-test (9HPT) and 3 blind assessed upper extremity writing and copying tasks. We neither found significant improvement in the upper extremity tests nor in the subjective response of the patients. In conclusion we could not confirm a beneficial effect of ondansetron on cerebellar tremor of MS patients.
