Metaxalone

Not to be confused with Metolazone, a diuretic.

Metaxalone, sold under the brand name Skelaxin, is a muscle relaxant medication used to relax muscles and relieve pain caused by strains, sprains, and other musculoskeletal conditions.^[1] Its exact mechanism of action is not known, but it may be due to general central nervous system depression.^[1] It is a moderately strong muscle relaxant, with relatively low incidence of side effects.^{[citation needed]}

Metaxalone

Clinical data
Trade names	Skelaxin
AHFS/Drugs.com	Monograph
MedlinePlus	a682010
License data	US DailyMed: Metaxalone
Routes of administration	By mouth
ATC code	None
Legal status
Legal status	US: ℞-only[1]
Pharmacokinetic data
Bioavailability	Unknown
Metabolism	Liver
Elimination half-life	9.2 ± 4.8 hours
Excretion	Kidney
Identifiers
IUPAC name 5-[(3,5-dimethylphenoxy)methyl]-1,3-oxazolidin-2-one
CAS Number	1665-48-1 Y
PubChem CID	15459
IUPHAR/BPS	7609
DrugBank	DB00660 Y
ChemSpider	14709 Y
UNII	1NMA9J598Y
KEGG	D00773 Y
ChEMBL	ChEMBL1079604 Y
CompTox Dashboard (EPA)	DTXSID3023269
ECHA InfoCard	100.015.253
Chemical and physical data
Formula	C12H15NO3
Molar mass	221.256 g·mol−1
3D model (JSmol)	Interactive image
SMILES O=C2OC(COc1cc(cc(c1)C)C)CN2
InChI InChI=1S/C12H15NO3/c1-8-3-9(2)5-10(4-8)15-7-11-6-13-12(14)16-11/h3-5,11H,6-7H2,1-2H3,(H,13,14) Y Key:IMWZZHHPURKASS-UHFFFAOYSA-N Y
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Common side effects include nausea, vomiting, drowsiness, and central nervous system (CNS) side effects, such as dizziness, headache, and irritability.^[1]

The metabolism of metaxalone involves enzymes CYP1A2 and CYP2C19 in the cytochrome P450 system. ^{[medical citation needed]} Because many medications are metabolized by enzymes in this system, precaution must be taken when administering it with other medications involving the P450 system to avoid interactions.^[2]

Because of the potential for side effects, this drug is considered high risk in the elderly.^{[medical citation needed]}

Pharmacokinetics

Metaxalone exhibits increased bioavailability when taken with food.^[3] Specifically, in one study, compared to fasted conditions, the presence of food at the time of drug administration increased C_max by 77.5%, AUC_0-t by 23.5%, and AUC_0-∞ by 15.4%.^[4] Metaxalone is a substrate of CYP1A2 and CYP2C19, an inhibitor of CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A, and an inducer of CYP1A2 and CYP3A4.^[2]

Assay

A literature survey reveals very few methods are reported for the determination of metaxalone to date. Nirogi et al.^[4] reported a liquid chromatographic method coupled to tandem mass spectrometry for the quantification of metaxalone in human plasma. A stability-indicating HPLC method was introduced by P. K. Sahu et al.^[5] Metaxalone has been used as an internal standard for few analytical methods.^[6][7]