Skeletal muscle relaxants are drugs that relax striated muscles (those that control the skeleton).
The term "muscle relaxant" is used to refer to 2 major therapeutic groups:
1) Neuromuscular Blockers
2) Spasmolytics
Neuromuscular Blockers act by interfering with transmission at the neuromuscular end plate and have no CNS activity. They are often used during surgical procedures and in intensive care and emergency medicine to cause paralysis.
Spasmolytics, also known as "centrally-acting" muscle relaxants, are used to alleviate musculoskeletal pain and spasms and to reduce spasticity in a variety of neurological conditions.
1) Skeletal muscle relaxants may be used for relief of spasticity in neuromuscular diseases such as multiple sclerosis, as well as for spinal cord injury and stroke.
2) They may also be used for pain relief in minor strain injuries and control of the muscle symptoms of tetanus.
The muscle relaxants are divided into 2 groups:
1. Centrally Acting
2. Peripherally Acting
The centrally acting group appears to act on the central nervous system (CNS), and contains 10 drugs that are chemically different. Only dantrolene has a direct action at the level of the nerve-muscle connection.
Baclofen (Lioresal) may be administered orally or intrathecally (introduced into the space under the arachnoid membrane that covers the brain and spinal cord) for control of spasticity due to neuromuscular disease.
LIST OF MUSCLE RELAXANTS
These drugs are used primarily as an adjunct for rest in management of acute muscle spasms associated with sprains.
Diazepam and methocarbamol are also used by injection for relief of tetanus.
All drugs in the muscle relaxant class may cause sedation.
Note: Baclofen, when administered intrathecally, may cause severe CNS depression with cardiovascular collapse and respiratory failure.
Dantrolene has a potential for hepatotoxicity. The incidence of symptomatic hepatitis is dose related, but may occur even with a short period of doses at or above 800 mg per day, which greatly increases the risk of serious liver injury.
Tizanidine may cause low blood pressure, but this may be controlled by starting with a low dose and increasing it gradually.
Methocarbamol and chlorzoxazone may cause harmless color changes in urine—orange or reddish purple with chlorzoxazone; and purple, brown, or green with methocarbamol.
The urine will return to its normal color when the patient stops taking the medicine.