Centrally acting muscle relaxants reduce muscle tone and tension by interfering with the postsynaptic reflexes in the central nervous system.
Centrally acting drugs are classified into spasmolytic and antispasmodic drugs. Spasmolytic drugs such as baclofen, diazepam, and tizanidine inhibit spinal motor neurons and decrease muscle tone. Spasmolytic drugs are administered for severe and chronic spasms due to multiple sclerosis, cerebral palsy, stroke, and spinal cord and muscle injuries. However, side effects like sedation, weakness, hypotension, and spasticity upon drug withdrawal may occur.
Cyclobenzaprine, methocarbamol, and orphenadrine are examples of antispasmodic drugs. They primarily act on the brain stem and reduce hyperactive muscle reflexes. Antispasmodic drugs are given orally to treat acute spasms due to muscle injury, trauma, and inflammation. Their side effects can include strong antimuscarinic effects like constipation, bradycardia, and urinary retention.
