Other Central Muscle Relaxants
· Chlormezanone use is associated with drowsiness, weak-ness, nausea, vertigo, skin rash, confusion, and dry mouth. Anticholinergic effects (mydriasis, hot, dry skin), coma, flac-cidity, and absent reflexes have been reported. Rarely it may cause Stevens-Johnson syndrome, erythema multiforme, and cholestatic jaundice. Several cases of hepatitis associated with therapeutic use of chlormezanone have been reported. As of November, 1996, Sanofi Winthrop manufacturers worldwide have voluntarily instituted a recall of all products which contain chlormezanone, due to toxic epidermal necrolytic reactions.
· Chlorzoxazone may induce anaphylactoid reactions, drowsi-ness, vertigo, GI disturbances, headache, skin rash, and jaundice.
· Tizanidine use may result in drowsiness, vertigo, nausea, drymouth, insomnia, headache, mild hypotension, and bradycardia. It is a centrally acting (alpha2-adrenergic agonist) muscle relaxant structurally related to clonidine, and is a short-acting drug used to treat spasticity. In a retrospective study, hypotension was observed in 8 of 45 patients following tizanidine overdose, while bradycardia was observed in 14 patients. Palpitations, ventricular extrasystoles, rash, sweating, skin ulcer, pruritus, vomiting, dyspepsia, abdominal pain, diarrhoea, constipation, elevated liver enzymes, back pain, lethargy, anxiety, syncope, tremor, depression, weakness, paraesthesia, miosis, visual hallu-cinations, and fever are uncommon adverse effects. Dryness of the mouth has been observed relatively frequently during tizanidine therapy, particularly during initiation of therapy. This effect generally subsides with continued administration. Concurrent administration of tizanidine and ethanol may result in additive central nervous system depression.
· Methocarbamol is a carbamate derivative used for thesymptomatic relief of muscle spasm. Toxicity results when blood levels exceed 40 mcg/ml. Symptomatology manifests as hypotension, bradycardia, convulsions, diplopia, headache, and vomiting.
· Metaxalone can cause muscle rigidity and CNS depression.