Centrally acting oral skeletal muscle relaxants.

A critical examination of the literature on centrally acting, orally administered skeletal muscle relaxants (SMRs) is presented. The available comparative clinical studies are reviewed, and the pharmacology, metabolism and adverse effects of the oral SMRs are discussed briefly. The drugs covered are carisoprodol, chlorphenesin carbamate, chlorzoxazone, cyclobenzaprine hydrochloride, diazepam, metaxalone, methocarbamol, and orphenadrine citrate. The mechanism of action of these agents is not well defined, and their effects are measured mainly by subjective responses. Thus, acceptable evidence of efficacy is difficult to obtain, especially if clinical studies continue to be designed inadequately. There are inadequate data to support the superiority of any one drug. Further, unique clinical efficacy of any oral SMR in comparison to nonspecific sedation has not been established. Based on subjective responses, all agents, except diazepam, have been shown to be superior to placebo in acute disorders; cyclobenzaprine has not been evaluated in acute conditions. SMRs are less effective in chronic disorders. Combination muscle relaxant-analgesic products appear to be superior to their individual components, but the relative efficacy of these combination products in comparison to combined use of individual sedative and analgesic agents is unknown.