Inefficacy of propranolol in attenuation of drug-induced parkinsonian tremor.

We investigated the tremolytic effect of long-acting propranolol (propranolol-LA) in six subjects with drug-induced parkinsonism (DIP), using a double-blind, placebo-controlled, crossover experimental design. Subjects received propranolol-LA for 2 weeks and placebo for 2 weeks, with no change in neuroleptic treatment. Tremor frequency and amplitude were objectively quantified at the end of each 2-week period by computerized tremorgram recording. There were no significant differences in attenuation of DIP tremor by propranolol-LA and placebo. Previous investigations reported in the literature have found propranolol to attenuate the tremor of idiopathic parkinsonism (IPD). It is expected that DIP and IPD tremor would respond similarly to propranolol if a solely peripheral or spinal cord tremolytic action were operative. A possible differential attenuation of IPD tremor and DIP tremor provides support for the concept of a higher central tremolytic mechanism of beta-adrenergic receptor-blocking drugs.