Metaxalone is a centrally-acting skeletal muscle relaxant used as an adjunct to rest, physical therapy, and other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions. It is a methanesulfonanilide derivative. Its precise mechanism is not fully understood but is believed to involve central nervous system depression, leading to sedative properties and a reduction of tonic somatic motor activity, influencing both polysynaptic and monosynaptic reflexes.
Adult: 800 mg (two 400 mg tablets) three to four times daily. Typical regimen: One 400 mg tablet 3-4 times a day, though 800 mg doses are common.
Note: Administer orally with a full glass of water. Can be taken with or without food, but taking with food may reduce GI upset. Do not crush or chew unless advised. Complete the prescribed course as an adjunct to rest and physiotherapy.
The exact mechanism of action of metaxalone is not fully elucidated. It does not directly relax tense skeletal muscles. Its clinical effects are believed to be due to general central nervous system (CNS) depression. It may produce its effect via sedative properties and by blocking neuronal activity within the descending reticular formation and spinal cord, leading to a reduction in somatic motor activity and modification of central perception of pain without affecting the stretch reflex.
Pregnancy: Category C: Animal reproduction studies have not been conducted. Use during pregnancy only if the potential benefit justifies the potential risk to the fetus. Avoid in first trimester unless absolutely necessary.
Driving: ADVISE NOT TO DRIVE or operate heavy machinery. Metaxalone causes drowsiness and dizziness which can impair mental and/or physical abilities.
| CNS Depressants (Alcohol, Benzodiazepines, Opioids) | Additive CNS depression, increased risk of sedation, respiratory depression, impaired psychomotor performance. | Major |
| CYP450 Inducers (e.g., Rifampicin, Carbamazepine, Phenytoin) | May increase metabolism of metaxalone, reducing its plasma concentration and efficacy. | Moderate |
| CYP450 Inhibitors (e.g., Ciprofloxacin, Fluconazole, Cimetidine) | May decrease metabolism of metaxalone, increasing its plasma concentration and risk of adverse effects. | Moderate |
| MAO Inhibitors (e.g., Phenelzine, Selegiline) | Theoretical risk of serotonin syndrome or hypertensive crisis; avoid combination. | Major |
| Other Serotonergic Drugs (e.g., SSRIs, SNRIs, Tramadol) | Increased risk of serotonin syndrome. | Moderate |
Same composition (Metaxalone (400mg)), different brands: