Metaxalone

Metaxalone

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Systematic (IUPAC) name
5-[(3,5-dimethylphenoxy)methyl]-1,3-oxazolidin-2-one
Clinical data
Pregnancy category	US: C (Risk not ruled out)
Routes of administration	Oral
Legal status
Legal status	US: ℞-only
Pharmacokinetic data
Bioavailability	Unknown
Metabolism	Hepatic
Biological half-life	9.2 (± 4.8) hours
Excretion	Renal
Identifiers
CAS Number	1665-48-1
ATC code	none
PubChem	CID 15459
DrugBank	APRD00514
Chemical data
Formula	C12H15NO3
Molar mass	221.252 g/mol[[]]
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Not to be confused with Metolazone, a diuretic.

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.

Metaxalone exhibits increased bioavailability when taken with food. Specifically, in one study, compared to fasted conditions, the presence of food at the time of drug administration increased C(max) by 177.5% and increased AUC(last) by 123.5% and AUC(inf) by 115.4%. Thus, based on the information in the labeling, patients receiving metaxalone therapy are directed to take metaxalone with food, and are informed that taking metaxalone with food results in an increase in the oral bioavailability of metaxalone compared to taking metaxalone without food.

Metabolism of metaxalone involves the liver cytochrome P450 system. Based on the information in the labeling, patients receiving metaxalone therapy and physicians prescribing metaxalone are directed to take precaution when co-administering with other medications involving the P450 system.

Because of potential for side effects, this drug is on the list for High Risk Medications in the elderly. (See NCQA’s HEDIS Measure: Use of High Risk Medications in the Elderly, http://www.ncqa.org/Portals/0/Newsroom/SOHC/Drugs_Avoided_Elderly.pdf).

External links

• Skelaxin (manufacturer's website)
• skelaxin_side_effects.htm uncited reports of side effects