Muscle spasm is one of the most common musculoskeletal complaints, and usually involve the neck, back or extremities. Muscle spasms and spasticity can be caused by neurological disorders such as multiple sclerosis, muscular dystrophy or nervous system trauma, as well as musculoskeletal conditions such as back strain, degenerative joint disease, tension headaches and fibromyalgia, notes the American Academy of Family Physicians. Both underlying causes can result in significant pain and limitation of movement. Muscle relaxants are sometimes used for relief of muscle spasms when acetaminophen or nonsteroidal anti-inflammatory drugs have failed.
Types
Muscle relaxants can be divided into two broad categories: antispasmotic agents mainly used to treat musculoskeletal-related muscle spasm, and antispasticity drugs used for neurologically-mediated muscle spasticity. Examples of antispasmotic drugs include cyclobenzaprine, metaxalone, carisoprodol, orphenadrine, chlorzoxazone and methocarbamol. Antispasticity drug examples include baclofen and dantrolene. Some drugs, including tizanidine and diazepam, are approved to treat both spasms and spasticity.
Function
Muscle relaxants come from a wide variety of drug classes, including antihistamines, tricyclic antidepressants, central alpha-2 adrenergic agonists, central nervous system depressants and gamma-aminobutyric acid, or GABA, agonists. Exactly how these drugs work to relieve the symptoms of muscle spasm is not known; however, according to PubMed, all cause sedation, which may contribute to their effectiveness as muscle relaxers.
Considerations
In comparison studies, baclofen and tizanidine appear to be effective in treating muscle spasticity, according to PubMed. There are insufficient studies comparing dantrolene to other available agents. Cyclobenzaprine is the most studied antispasmotic medication, as reported by the American Academy of Family Physicians, and is effective in treating neck and back muscle spasms when compared to a placebo in all studies. The only other antispasmotic drugs demonstrated to be more effective than a placebo include tizanidine, carisoprodol and orphenadrine.
Side Effects
Muscle relaxants have many different modes of action, and thus many different side effects. All muscle relaxants appear to be equally tolerated, and all cause sedation, though some--particularly carisoprodol and diazepam--more than others. Dizziness, confusion, nausea and vomiting are other commonly shared side effects. Muscle relaxants are metabolized by the liver and excreted out of the body by the kidneys, and should therefore be used with great caution in patients with liver or kidney disease, according to "P & J Journal." Severe liver damage may occur with dantrolene, as well as other liver-toxic effects from tizanidine and chlorzoxazone.
Warning
According to "P & T Journal," carisoprodol has the highest potential for abuse because it is metabolized to meprobamate, a controlled substance which causes physical and psychological dependence. Carisoprodol has also been reported to be used by substance abusers to augment the effect of alcohol and alprazolam. Diazepam, like all benzodiazepines, also has significant abuse potential. Because of the potential for abuse and lack of superiority over other muscle relaxants, carisoprodol and diazepam are usually used only after other drugs have failed.
