{{Short description|Muscle relaxant}} {{distinguish |text= Metolazone, a diuretic}} {{Drugbox | verifiedrevid = 458442143 | image = Metaxalone.svg | image_class = skin-invert-image | width = 200 | alt = | caption = <!--Clinical data--> | tradename = Skelaxin | Drugs.com = {{drugs.com|monograph|metaxalone}} | MedlinePlus = a682010 | DailyMedID = Metaxalone | pregnancy_US = N | legal_US = Rx-only | legal_US_comment = <ref name="Skelaxin FDA label" /> | routes_of_administration = By mouth | ATC_prefix = None | ATC_suffix = <!--Pharmacokinetic data--> | bioavailability = Unknown | protein_bound = | metabolism = Liver | elimination_half-life = 9.2&nbsp;±&nbsp;4.8 hours | excretion = Kidney <!--Identifiers--> | CAS_number_Ref = {{cascite|correct|??}} | CAS_number = 1665-48-1 | PubChem = 15459 | IUPHAR_ligand = 7609 | DrugBank_Ref = {{drugbankcite|correct|drugbank}} | DrugBank = DB00660 | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 14709 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = 1NMA9J598Y | KEGG_Ref = {{keggcite|correct|kegg}} | KEGG = D00773 | ChEMBL_Ref = {{ebicite|correct|EBI}} | ChEMBL = 1079604 <!--Chemical data--> | IUPAC_name = 5-[(3,5-dimethylphenoxy)methyl]-1,3-oxazolidin-2-one | C=12 | H=15 | N=1 | O=3 | smiles = O=C2OC(COc1cc(cc(c1)C)C)CN2 | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 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) | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = IMWZZHHPURKASS-UHFFFAOYSA-N }} '''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.<ref name="Skelaxin FDA label">{{cite web | title=Skelaxin- metaxalone tablet | work = DailyMed | publisher = U.S. National Library of Medicine | date=27 April 2018 | url=https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7a4163f2-c553-4d14-7e98-d14c5c7f772a | access-date=23 October 2020}}</ref> Its exact mechanism of action is not known, but it may be due to general central nervous system depression.<ref name="Skelaxin FDA label" /> It is a moderately strong muscle relaxant, with relatively low incidence of side effects.{{Cn|date=May 2022}}

Common side effects include nausea, vomiting, drowsiness, and central nervous system (CNS) side effects, such as dizziness, headache, and irritability.<ref name="Skelaxin FDA label" />

The metabolism of metaxalone involves enzymes CYP1A2 and CYP2C19 in the cytochrome P450 system. {{medcn|date=October 2020}} 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.<ref name=label_change_patent>{{cite patent | country = US | number = 7378434 | url = https://patents.google.com/patent/US7378434 | title = Metaxalone products, method of manufacture, and method of use | inventor = Du J, Roberts RH | assign1 = Takeda Pharmaceuticals USA Inc. | gdate = 27 May 2008 }}</ref>

Because of the potential for side effects, this drug is considered high risk in the elderly.{{medcn|date=October 2020}}

==Pharmacokinetics== Metaxalone exhibits increased bioavailability when taken with food.<ref>{{cite web | url = http://www.kingpharm.com/products/product_document.cfm?brand_name=Skelaxin&product_specific_name=&document_type_code=PI | archive-url = https://web.archive.org/web/20100309050550/http://www.kingpharm.com/products/product_document.cfm?brand_name=Skelaxin&product_specific_name=&document_type_code=PI | archive-date = 9 March 2010 | title = Skelaxin Package Insert | publisher = King Pharmaceuticals, Inc. }}</ref> Specifically, in one study, compared to fasted conditions, the presence of food at the time of drug administration increased C<sub>max</sub> by 77.5%, AUC<sub>0-t</sub> by 23.5%, and AUC<sub>0-∞</sub> by 15.4%.<ref name="pmid16803662">{{cite journal | vauthors = Nirogi RV, Kandikere VN, Shukla M, Mudigonda K, Shrivastava W, Datla PV | title = Quantification of metaxalone in human plasma by liquid chromatography coupled to tandem mass spectrometry | journal = Journal of Analytical Toxicology | volume = 30 | issue = 4 | pages = 245–251 | date = May 2006 | pmid = 16803662 | doi = 10.1093/jat/30.4.245 | doi-access = free }}</ref> 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.<ref name=label_change_patent />

==Assay== A literature survey<!-- <ref>Prafulla Kumar Sahu and M. Mathrusri Annapurna, Analytical method development by liquid chromatography, LAP Lambert Academic Publisher, Germany, 2011 ISBN 3-8443-2869-6. [https://www.lap-publishing.com/catalog/details/store/gb/book/978-3-8443-2869-1/analytical-method-development-by-liquid-chromatography]</ref> --> reveals very few methods are reported for the determination of metaxalone to date. Nirogi et al.<ref name="pmid16803662" /> 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.<ref>{{cite journal | vauthors = Sahu PK, Annapurna MM, Kumar SD |title=Development and Validation of Stability Indicating RP-HPLC Method for the Determination of Metaxalone in Bulk and its Pharmaceutical Formulations |journal=e-Journal of Chemistry |date=2011 |volume=8 |issue=s1 |pages=S439–S447 |doi=10.1155/2011/645710 |doi-access=free }}</ref> Metaxalone has been used as an internal standard for few analytical methods.<ref>{{cite journal | vauthors = Mistri HN, Jangid AG, Pudage A, Gomes N, Sanyal M, Shrivastav P | title = High throughput LC-MS/MS method for simultaneous quantification of lamivudine, stavudine and nevirapine in human plasma | journal = Journal of Chromatography. B, Analytical Technologies in the Biomedical and Life Sciences | volume = 853 | issue = 1–2 | pages = 320–332 | date = June 2007 | pmid = 17481969 | doi = 10.1016/j.jchromb.2007.03.047 }}</ref><ref>{{cite journal | vauthors = Mistri HN, Jangid AG, Pudage A, Shrivastav P | title = HPLC-ESI-MS/MS validated method for simultaneous quantification of zopiclone and its metabolites, N-desmethyl zopiclone and zopiclone-N-oxide in human plasma | journal = Journal of Chromatography. B, Analytical Technologies in the Biomedical and Life Sciences | volume = 864 | issue = 1–2 | pages = 137–148 | date = March 2008 | pmid = 18313371 | doi = 10.1016/j.jchromb.2008.02.004 }}</ref>

== References == {{reflist}}

== External links == * {{cite web | url = https://druginfo.nlm.nih.gov/drugportal/name/metaxalone | archive-url = https://web.archive.org/web/20190628221758/https://druginfo.nlm.nih.gov/drugportal/name/metaxalone | url-status = dead | archive-date = June 28, 2019 | publisher = U.S. National Library of Medicine | work = Drug Information Portal | title = Metaxalone }}

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Category:Muscle relaxants Category:Carbamates Category:Oxazolidines Category:Drugs developed by Pfizer Category:Phenol ethers Category: Drugs with unknown mechanisms of action