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1. Dantrolene, Dantrium, Dantamacrin, Dantrolen
Dantrolene sodium is a muscle relaxant that acts by abolishing excitation-contraction coupling in muscle cells, probably by action on the ryanodine receptor and decreasing free intracellular calcium concentration. It is the only specific and effective treatment for malignant hyperthermia, a rare, life-threatening disorder triggered by general anesthesia. It is also used in the management of neuroleptic malignant syndrome, muscle spasticity (e.g. after strokes, in paraplegia, cerebral palsy, or patients with multiple sclerosis), 3,4-methylenedioxymethamphetamine ("ecstasy") intoxication, serotonin syndrome, and 2,4-dinitrophenol poisoning. Chemically it is a hydantoin derivative, but does not exhibit antiepileptic activity like other hydantoin derivates such as phenytoin.
Central nervous system side effects are quite frequently noted and encompass speech and visual disturbances, mental depression and confusion, hallucinations, headache, insomnia, exacerbation or precipitation of seizures, and increased nervousness. Infrequent cases of respiratory depression or a feeling of suffocation have been observed. Dantrolene often causes sedation severe enough to incapacitate the patient to drive or operate machinery. Gastrointestinal effects include bad taste, anorexia, nausea, vomiting, abdominal cramps, and diarrhea.
Hepatic side effects may be seen either as asymptomatic elevation of liver enzymes and/or bilirubin or, most severe, as fatal and nonfatal hepatitis. The risk of hepatitis is associated with the duration of treatment and the daily dose. In patients treated for hyperthermia, no liver toxicity has been observed so far.
Pleural effusion with pericarditis (oral treatment only), rare cases of bone marrow damage, diffuse myalgias, backache, dermatologic reactions, transient cardiovascular reactions, and crystalluria have additionally been seen. Muscle weakness may persist for several days following treatment. Drugs.com
1. Schreiber AL, Vasudevan JM, Fetouh SK, Ankam NS, Hussain A, Rakocevic G. Atypical clinically diagnosed stiff-person syndrome response to dantrolene--a refractory case. Muscle Nerve. 2012 Mar;45(3):454-5. doi: 10.1002/mus.22331. Link to article
2. Carbamazepine, Tegretol, Equetro
Carbamazepine is an anticonvulsant and mood-stabilizing drug used primarily in the treatment of epilepsy and bipolar disorder, as well as trigeminal neuralgia. It is also used off-label for a variety of indications, including attention-deficit hyperactivity disorder (ADHD), schizophrenia, phantom limb syndrome, complex regional pain syndrome, paroxysmal extreme pain disorder, neuromyotonia, intermittent explosive disorder, borderline personality disorder, myotonia congenita and post-traumatic stress disorder.
The mechanism of action of carbamazepine and its derivatives is relatively well-understood. Carbamazepine stabilizes the inactivated state of voltage-gated sodium channels, making fewer of these channels available to subsequently open. This leaves the affected cells less excitable until the drug dissociates. Carbamazepine has also been shown to potentiate GABA receptors made up of alpha1, beta2, and gamma2 subunits. This may be relevant to its efficacy in neuropathic pain and manic-depressive illness. Drugs.com
3. Cyclobenzaprine, Flexeril, Fexmid, Amrix
Flexeril is a muscle relaxer used to relieve skeletal muscle spasms and associated pain in acute musculoskeletal conditions. It is the best-studied drug for this application. It has also been used off-label for fibromyalgia. The sedative effects are likely due to its antagonistic effect on histamine, serotonin, and muscarinic receptors. Drugs.com
4. Metaxalone, Skelaxin
Skelaxin is used to relax muscles and relieve pain caused by strains, sprains, and other musculoskeletal conditions. Its exact mechanism of action is not known, but it may be due to general central nervous system depression. It is considered to be a moderately strong muscle relaxant, with relatively low incidence of side effects. Drugs.com
5. Robaxin, Methocarbamol
Methocarbamol is a central muscle relaxant used to treat skeletal muscle spasms. The mechanism of action is currently unknown, but may involve the inhibition of carbonic anhydrase. The muscle relaxant effects of methocarbamol are largely attributed to central depressant effects; however, peripheral effects of methocarbamol to prolong muscle refractory period have also been reported. Unlike other carbamates, such as meprobamate and its prodrug carisoprodol, methocarbamol has greatly reduced abuse potential. Studies comparing it to lorazepam (Ativan) and diphenhydramine (Benadryl) along with placebo, find that methocarbamol produces increased "liking" responses and some sedative-like effects. However, at higher doses dysphoria is reported. It is considered to have an abuse profile similar to, but weaker than, lorazepam. Drugs.com.
1. Voci JM, al-Hakim M, Dokko Y, Katirji MB. Intravenous methocarbamol in the treatment of stiff-man syndrome. Muscle Nerve. 1993 Apr;16(4):434-5. Link to article
6. Tizanidine, Zanaflex, Sirdalud
Tizanidine is a centrally acting α2 adrenergic agonist. It is used to treat spasms, cramping, and tightness of muscles caused by medical problems such as multiple sclerosis, ALS, spastic diplegia, back pain, or certain other injuries to the spine or central nervous system. It is also prescribed off-label for migraine headaches, as a sleep aid, and as an anticonvulsant. It is also prescribed for some symptoms of fibromyalgia. Tizanidine has been found to be as effective as other antispasmodic drugs and has superior tolerability to that of baclofen and diazepam. Drugs.com.
1. Meinck HM, Ricker K, Conrad B. The stiff-man syndrome: new pathophysiological aspects from abnormal exteroceptive reflexes and the response to clomipramine, clonidine, and tizanidine. J Neurol Neurosurg Psychiatry 1984, 47:280–287. Link to article