A group of drugs that are used to treat muscular stiffness and cramps
Muscle relaxants are used for the relief of muscle spasm. They are also used to ease the movement of limbs that are stiff because of nervous system disorders such as multiple sclerosis and cerebral palsy. Muscle relaxants are sometimes prescribed to treat conditions such as night-time muscle cramps and torticollis. Certain muscle relaxants are used to paralyse muscles during surgery under general anaesthesia.
How do they work?
Muscle relaxant drugs work in a variety of ways. Some muscle relaxants, such as tizanidine, baclofen, and the antianxiety drug diazepam, work by reducing transmission of nerve signals from the brain and spinal cord to the muscles, causing the muscles to relax.
Dantrolene relieves spasm by acting directly on muscles and making them less sensitive to nerve signals from the brain and spinal cord. Botulinum toxin relaxes muscles by blocking the transmission of signals from nerve endings to muscle cells. The way in which quinine works is not fully understood.
How are they used?
Doses of muscle relaxants need careful adjustment. Too little has no effect, and too much may lead to muscle weakness. For long-standing conditions such as multiple sclerosis, doses begin at a low level and are increased gradually to reach a balance between symptom control and muscle strength.
Involuntary contractions of the neck and facial muscles can be relieved by injecting tiny amounts of botulinum toxin directly into the affected area. A single injection is usually effective for about 3 months. Quinine taken at bedtime, also in tiny amounts, helps to prevent cramp developing in the night.
What are the side effects?
A common side effect of many muscle relaxants is drowsiness, which usually decreases as treatment progresses. With long-term use, the body may become dependent on a muscle relaxant; if the drug is withdrawn suddenly, muscle spasms may become worse than they were before treatment began. Dantrolene can cause diarrhoea. This drug may also cause severe liver problems, as may tizanidine. If you are taking either of these drugs, your doctor will carry out regular blood tests to check your liver function.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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