DESCRIPCION

Metaxalone is an oral CNS depressant used as adjunct therapy for acute, painful musculoskeletal conditions. Although the drug is classified as a skeletal muscle relaxant, it does not directly relax skeletal muscle. Most of the beneficial effects of metaxalone are thought to be due to its sedative properties. Metaxalone does not effectively treat skeletal muscle hyperactivity secondary to chronic neurologic disorders (e.g., cerebral palsy). This drug was approved by the FDA in 1962. Mechanism of Action: The mechanism of action of metaxalone has not been established. Metaxalone has no direct effect on the contractile mechanism of striated muscle, the motor end plate, or the nerve fiber. Its mode of action may be related to its sedative properties. Pharmacokinetics: Metaxalone is administered orally, with mean peak plasma concentrations occurring about 2 hours after a single 800 mg dose. The onset of action is usually within 1 hour, and the duration of effect is about 4—6 hours. It is not known if metaxalone crosses the placenta or if it is distributed into milk. Metaxalone is metabolized by the liver and excreted in urine as unidentified metabolites. The elimination half-life is approximately 2—3 hours.

ndications...Dosage For use as an adjunct to rest, physical therapy, and other measures for the relief of acute, painful musculoskeletal conditions (e.g., muscle spasm): Oral dosage: Adults and adolescents: 800 mg PO three times daily or four times daily. Elderly: Avoid use in the elderly due to the potential for anticholinergic side effects, sedation, and weakness. Drug efficacy at doses tolerated in the elderly is questionable. Children, infants, and neonates: Safe and effective use has not been established. Maximum Dosage Limits: •Adults: 3200 mg/day PO. •Elderly: Not advised for use in the elderly due to potential anticholinergic effects. •Adolescents: 3200 mg/day PO. •Children: Safe and effective use has not been established. Patients with hepatic impairment: According to the manufacturer, metaxalone is contraindicated in patients with significant hepatic impairment. Patients with renal impairment: According to the manufacturer, metaxalone is contraindicated in patients with significant renal impairment. Intermittent hemodialysis: Not applicable. Metaxalone is contraindicated in patients with significant renal impairment.

Oral Administration •Administered with or without food.

CONTRAINDICACIONES

According to the manufacturer, metaxolone is contraindicated in patients with significant renal impairment or hepatic dysfunction (hepatic disease). The drug is also contraindicated in patients with a history of drug-induced hemolytic anemia or other types of anemia. Metaxalone is a CNS depressant. Patients should be cautioned about driving or operating machinery until the effects of the drug are known. Metaxalone is not advised for use in the elderly due to the potential for anticholinergic side effects, sedation, and weakness. The effectiveness of metaxalone at doses tolerated in the geriatric population is questionable. No FDA pregnancy category is available for metaxalone. Reproduction studies in rats revealed no evidence of impaired fertility or harm to the fetus due to metaxalone. Adequate and well-controlled studies have not been conducted in pregnant women. Metaxalone should only be used during pregnancy if the potential benefits outweigh the possible risk to the fetus. It is not known if metaxalone is distributed into human milk. Thus, metaxalone should be used with caution in a woman who is breast-feeding. Safety and effectiveness of metaxalone have not been established in children 12 years of age or younger.

INTERACCIONES

Concomitant administration of metaxalone with CNS depressants, including anxiolytics, sedatives, and hypnotics; barbiturates; benzodiazepines; opiate agonists; butorphanol; nalbuphine; pentazocine; phenothiazines; chlorpheniramine; clemastine; cyproheptadine; diphenhydramine; ethanol; hydroxyzine; promethazine; tricyclic antidepressants; tramadol; or the phytomedicinal herbs valerian, Valeriana officinalis or kava kava, Piper methysticum can potentiate the sedative effects of either agent.

REACCIONES ADVERSAS

The most frequent reactions to metaxalone include nausea/vomiting, GI upset, drowsiness, dizziness, headache, and anxiety or irritability. Hypersensitivity reactions have occurred and are characterized by maculopapular rash with or without pruritus. Leukopenia, hemolytic anemia, and jaundice have occurred rarely. Use of metaxalone has been associated with elevated hepatic enzymes such as increased serum concentrations of AST, ALT, alkaline phosphatase, and bilirubin. Liver function tests should be performed periodically in patients receiving metaxalone.

Metaxalone Skelaxin®