Metaxalone Drug Information

Metaxalone is indicated as an adjunct to rest, physical therapy, and other measures for the relief of discomforts associated with acute, painful musculoskeletal conditions. The mode of action of this drug has not been clearly identified, but may be related to its sedative properties. Metaxalone does not directly relax tense skeletal muscles in man.

The recommended dose for adults and children over 12 years of age is one 800 mg tablet three to four times a day.

• The most frequent reactions to metaxalone include: CNS : drowsiness, dizziness, headache, and nervousness or “irritability”; Digestive : nausea, vomiting, gastrointestinal upset.
• Other adverse reactions are: Immune System : anaphylaxis, hypersensitivity reaction, rash with or without pruritus; Hematologic : leukopenia; hemolytic anemia; Hepatobiliary : jaundice; CNS : cases of serotonin syndrome, a potentially life-threatening condition, have been reported during concomitant use of serotonergic drugs with metaxalone used within the recommended dosage range and with metaxalone as a single agent taken at doses higher than the recommended dose (see WARNINGS, PRECAUTIONS: Drug Interactions, and OVERDOSAGE ).

• Drug Interactions CNS Depressants: The sedative effects of Metaxalone and other CNS depressants (e.g., alcohol, benzodiazepines, opioids, tricyclic antidepressants (TCAs)) may be additive. Exercise caution with patients who take more than one of these CNS depressants simultaneously. Follow patients closely for signs and symptoms of respiratory depression and sedation (see WARNINGS ).
• Serotonergic Drugs: Serotonin syndrome has resulted from concomitant use of serotonergic drugs with Metaxalone used within the recommended dosage range (see WARNINGS ). If concomitant use is warranted, carefully observe the patient, particularly during treatment initiation and dose adjustment. Discontinue Metaxalone if serotonin syndrome is suspected.
• Examples of serotonergic drugs include: selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), triptans, 5-HT3 receptor antagonists, opioids (particularly fentanyl, meperidine, and methadone), drugs that affect the serotonin neurotransmitter system (e.g., mirtazapine, trazodone, tramadol), monoamine oxidase (MAO) inhibitors (those intended to treat psychiatric disorders and also others, such as linezolid and intravenous methylene blue).

Pregnancy Reproduction studies in rats have not revealed evidence of impaired fertility or harm to the fetus due to metaxalone. Post marketing experience has not revealed evidence of fetal injury, but such experience cannot exclude the possibility of infrequent or subtle damage to the human fetus. Safe use of metaxalone has not been established with regard to possible adverse effects upon fetal development.

Therefore, metaxalone tablets should not be used in women who are or may become pregnant and particularly during early pregnancy unless, in the judgement of the physician, the potential benefits outweigh the possible hazards.

Pediatric Use Safety and effectiveness in children 12 years of age and below have not been established.

Known hypersensitivity to any components of this product. Known tendency to drug induced, hemolytic, or other anemias. Significantly impaired renal or hepatic function.

Deaths by deliberate or accidental overdose have occurred with metaxalone, particularly in combination with antidepressants, and have been reported with this class of drug in combination with alcohol. Serotonin syndrome has been reported when metaxalone was used at doses higher than the recommended dose (see WARNINGS and ADVERSE REACTIONS ). When determining the LD 50 in rats and mice, progressive sedation, hypnosis, and finally respiratory failure were noted as the dosage increased. In dogs, no LD 50 could be determined as the higher doses produced an emetic action in 15 to 30 minutes.

Treatment - Gastric lavage and supportive therapy. Consultation with a regional poison control center is recommended.