Centrally Acting Skeletal Muscle Relaxants

What is the prototype?

Baclofen

• Given PO or intrathecal

Why is it prescribed?

• Baclofen: tx of muscle spasticity assoc. with neuromuscular diseases and spinal cord injury

• Cyclobenzaprine, metaxalone, tizanidine, methocarbamol: tx of acute musculoskeletal spasms

How does it work?

Works in the CNS to interfere with the neurons controlling muscle reflexes causing spams

What happens if it works too well?

Since these work on the CNS, oversedation, coordination problems, falls, insomnia, and suppression of the parasympathetic nervous system (i.e., dry mouth, constipation, anorexia, and arrhythmias though rare) may occur

What is special about it (4)?

• Tizanidine: possible liver toxicity and hypotension

• Chlorzoxazone: can turn urine purple or orange

• Metaxalone: only type for children <12 yrs old

• DI: any sedating substance (i.e., opiates, ETOH, benzodiazepines, etc.) should be not be combined with muscle relaxants