Skeletal muscle tremor and the influence of adrenergic drugs

Physiologic postural skeletal muscle tremor is enhanced by beta 2 receptor agonist such as those used in the treatment of asthma. This is a peripheral response rather than one occurring at the central nervous system level. It is greatest when drugs are administered by the oral or parenteral routes, and is the most important dose-limiting factor for oral administration. Clinically important tremor is minimal after aerosolized administration of clinically recommended doses of aerosolized beta 2 receptor agonists, but can be significant when larger doses are administered. Sympathomimetic drugs which can selectively stimulate airway beta 2 receptors, as opposed to skeletal muscle beta 2 receptors, do not currently exist. Combining orally administered beta 2 agents with theophylline potentiates the effects on muscle tremor. There does not seem to be a clinical advantage, in terms of reduced side effects such as muscle tremor, to combining "small doses" of oral beta agonists and theophylline as opposed to using either agent alone in optimal doses. Tolerance to the tremoregenic effects of beta 2 agonists appears to occur when these agents are administered on a chronic basis. Thus, there may be some rationale for beginning oral beta agonists initially with lower doses and progressively increasing to full doses over a period of days to weeks.