Drug Groups

approved

Description

Metaxalone (marketed by King Pharmaceuticals under the brand name Skelaxin?) is a muscle relaxant 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. Skelaxin comes in an 800 mg scored tablet. It previously came in both 400 mg and 800 mg tablets. The 400 mg tablet has been discontinued. Possible side effects include nausea, vomiting, drowsiness and CNS side effects such as dizziness, headache, and irritability.

Indication

For the treatment of painful peripheral musculoskeletal conditions and spasticity from upper motor neuron syndromes.

Pharmacology

Metaxalone is a skeletal muscle relaxant 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.

Toxicity

LD₅₀=775mg/kg (Rat, oral); LD₅₀=1690 mg/kg (Mouse, oral). When determining the LD₅₀ in rats and mice, progressive sedation, hypnosis and finally respiratoryfailure were noted as the dosage increased. In dogs, no LD₅₀ could be determined as the higher doses produced an emetic action in 15 to 30 minutes.

Affected Organisms

Biotransformation

Probably hepatic.

Absorption

The absolute bioavailability of metaxalone from Skelaxin tablets is not known.

Half Life

9.2 (+/- 4.8) hours

Elimination

Metaxalone is metabolized by the liver and excreted in the urine as unidentified metabolites.

Distribution

* 800 L

Clearance

* 68 +/- 50 L/h [Subjects received 1×400mg tablet under fasted conditions]
* 66 +/- 51 L/h [Subjects received 2×400 mg tablets under fasted conditions]

References

External Links