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A muscle spasm is an acute condition caused by sudden and involuntary contraction of an individual muscle or a group of muscles. It is usually associated with a partial tear of the involved muscle (muscle strain) or the rupture of a ligament (muscle sprain). Skeletal muscle relaxants are a group of medicines that help provide relief from the muscle spasm. They act in three ways:

  • They help to reduce muscle excitability
  • They help to reduce pain
  • They help in improving motor function

All skeletal muscle relaxants act on the central nervous system. This means that they exert their effect at the level of the cerebrum, brain stem or the spinal cord. They have a negligible effect at the level of the muscle fiber.

Based on their primary function, skeletal muscle relaxants have been grouped under two major categories:

  • Antispasmodic agents
  • Antispastic agents

Antispasmodic muscle relaxants

These muscle relaxants are primarily used to treat peripheral musculoskeletal conditions. They help to relieve muscle spasms and pain caused by conditions like fibromyalgia, myofascial pain syndrome, tension headaches, low backache and neck pain.

The muscular spasms in these conditions are not associated with hypertonicity and hyperreflexia but can produce a considerable functional disability. The skeletal muscle relaxants used to manage peripheral musculoskeletal conditions include carisoprodol (Soma), chlorzoxazone (Paraflex), metaxalone (Skelaxin), methocarbamol (Robaxin) and orphenadrine (Norflex).

Antispastic muscle relaxants

In conditions like multiple sclerosis and injuries to the spinal cord, there is damage to the upper motor neurons. This may cause spasticity, stiffness of muscles and awkward movements. The FDA has approved only a few skeletal muscle relaxants for treating spasticity. These muscle relaxants include baclofen (Lioresal), dantrolene (Dantrium) and tizanidine (Zanaflex).

Let us look into details of two of the commonly prescribed skeletal muscle relaxants used for treating peripheral musculoskeletal conditions namely, Soma and Robaxin.

Soma (Carisoprodol)

This drug primarily acts by inhibiting the interneuronal transmission of pain sensations between the spinal cord and the descending reticular formation.

Soma is metabolized into meprobamate, a controlled substance with abuse potential. Soma should be taken only when prescribed by a doctor and only in the prescribed doses. It should never be stopped suddenly, but should rather be tapered off gradually.

It can produce drowsiness and dizziness and slows down thinking and reactions. As it is a habit-forming drug, Soma is only used to treat those painful musculoskeletal conditions that last for a short duration.

Robaxin (Methocarbamol)

This is a skeletal muscle relaxant that acts by blocking the pain sensations sent to the brain. It can cause blurry vision, hypotension, nasal congestion, dizziness and headache.

Soma and Robaxin both treat the same peripheral musculoskeletal disorders, so the medication of choice depends on an individual's response to the drug. While some patients respond well to Soma, others prefer Robaxin.

However, physicians tend to avoid prescribing Soma because of its abuse potential. Moreover, if the patient has to work throughout the day despite his pain, it is better to prescribe Robaxin. This is because Soma has a more profound effect on thinking and reaction and is more likely to cause drowsiness.

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