DRUGS USED TO TREAT ACUTE LOCAL MUSCLE SPASM
A large number of less well-studied, centrally active drugs (eg, carisoprodol, chlorphenesin, chlorzoxazone, cycloben-zaprine, metaxalone, methocarbamol, and orphenadrine)are promoted for the relief of acute muscle spasm caused by local tissue trauma or muscle strains. It has been suggested that these drugs act primarily at the level of the brainstem. Cyclobenzaprine may be regarded as the prototype of the group. Cyclobenzaprine is structurally related to the tricyclic antidepressants and produces antimuscarinic side effects. It is ineffective in treating muscle spasm due to cerebral palsy or spinal cord injury. As a result of its strong antimuscarinic actions, cyclobenzaprine may cause significant sedation, as well as confusion and transient visual hallucinations. The dosage of cyclobenzaprine for acute injury-related muscle spasm is 20–40 mg/d orally in divided doses.