Metaxalone, sold under the brand name Skelaxin, is a

muscle relaxant A muscle relaxant is a drug that affects skeletal muscle function and decreases the muscle tone. It may be used to alleviate symptoms such as muscle spasms, pain, and hyperreflexia. The term "muscle relaxant" is used to refer to two major therapeu ...

medication used to relax muscles and relieve pain caused by strains,

sprain A sprain is a soft tissue injury of the ligaments within a joint, often caused by a sudden movement abruptly forcing the joint to exceed its functional range of motion. Ligaments are tough, inelastic fibers made of collagen that connect two or ...

s, and other musculoskeletal conditions. Its exact mechanism of action is not known, but it may be due to general

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...

depression. It is a moderately strong muscle relaxant, with relatively low incidence of side effects. Common side effects include nausea, vomiting, drowsiness, and

(CNS) side effects, such as dizziness, headache, and irritability. The metabolism of metaxalone involves enzymes CYP1A2 and CYP2C19 in the

cytochrome P450 Cytochromes P450 (P450s or CYPs) are a Protein superfamily, superfamily of enzymes containing heme as a cofactor (biochemistry), cofactor that mostly, but not exclusively, function as monooxygenases. However, they are not omnipresent; for examp ...

system. 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. Because of the potential for side effects, this drug is considered high risk in the elderly.

Pharmacokinetics

Metaxalone exhibits increased

bioavailability In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation. By definition, when a medication is administered intravenously, its bioavailability is 100%. H ...

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 77.5%, AUC_0-t by 23.5%, and AUC_0-∞ by 15.4%. Metaxalone is a substrate of CYP1A2 and CYP2C19, an inhibitor of CYP1A2, CYP2B6, CYP2C9, CYP2C19,

CYP2D6 Cytochrome P450 2D6 (CYP2D6) is an enzyme that in humans is encoded by the ''CYP2D6'' gene. ''CYP2D6'' is primarily expressed in the liver. It is also highly expressed in areas of the central nervous system, including the substantia nigra. CYP2 ...

, CYP2E1, and CYP3A, and an inducer of CYP1A2 and

CYP3A4 Cytochrome P450 3A4 (abbreviated CYP3A4) () is an important enzyme in the body, mainly found in the liver and in the intestine, which in humans is encoded by ''CYP3A4'' gene. It organic redox reaction, oxidizes small foreign organic molecules ( ...

Assay

A literature survey reveals very few methods are reported for the determination of metaxalone to date. Nirogi ''et al.'' 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.'' Metaxalone has been used as an internal standard for few analytical methods.

References

External links

* {{Portal bar , Medicine Muscle relaxants Carbamates Oxazolidines Drugs developed by Pfizer Phenol ethers Drugs with unknown mechanisms of action