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2D Structure
Also known as: 1665-48-1, Skelaxin, Zorane, Methaxalonum, Metaxalon, Methoxolone
Molecular Formula
C12H15NO3
Molecular Weight
221.25  g/mol
InChI Key
IMWZZHHPURKASS-UHFFFAOYSA-N
FDA UNII
1NMA9J598Y

Metaxalone is an oxazolidinone with centrally-acting skeletal muscle relaxant properties. Although the exact mechanism through which metaxalone exerts its effect is largely unknown, it might be due to general central nervous system (CNS) depression. Metaxalone has no direct effect on the contractile mechanisms of striated muscle, the motor end plate, or the nerve fiber.
The physiologic effect of metaxalone is by means of Centrally-mediated Muscle Relaxation.
1 2D Structure

2D Structure

2 Identification
2.1 Computed Descriptors
2.1.1 IUPAC Name
5-[(3,5-dimethylphenoxy)methyl]-1,3-oxazolidin-2-one
2.1.2 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)
2.1.3 InChI Key
IMWZZHHPURKASS-UHFFFAOYSA-N
2.1.4 Canonical SMILES
CC1=CC(=CC(=C1)OCC2CNC(=O)O2)C
2.2 Other Identifiers
2.2.1 UNII
1NMA9J598Y
2.3 Synonyms
2.3.1 MeSH Synonyms

1. Ahr 438

2. Skelaxin

2.3.2 Depositor-Supplied Synonyms

1. 1665-48-1

2. Skelaxin

3. Zorane

4. Methaxalonum

5. Metaxalon

6. Methoxolone

7. 5-((3,5-dimethylphenoxy)methyl)oxazolidin-2-one

8. Metazalone

9. Metazolone

10. Metaxolone

11. Ahr-438

12. Metaxalonum [latin]

13. Metassalone [dcit]

14. 5-[(3,5-dimethylphenoxy)methyl]-1,3-oxazolidin-2-one

15. 2-oxazolidinone, 5-[(3,5-dimethylphenoxy)methyl]-

16. Ahr 438

17. Metaxalonum [inn-latin]

18. Metaxalona [inn-spanish]

19. Nsc 170959

20. 5-(3,5-xyloloxymethyl)oxazolidin-2-one

21. Cl 39,148

22. Flexura

23. 5-((3,5-xylyloxy)methyl)-2-oxazolidinone

24. 5-[(3,5-xylyloxy)methyl]-2-oxazolidinone

25. 2-oxazolidinone, 5-((3,5-xylyloxy)methyl)-

26. 5-((3,5-dimethylphenoxy)methyl)-2-oxazolidinone

27. Mfcd00867700

28. Nsc170959

29. 5-[(3,5-dimethylphenoxy)methyl]oxazolidin-2-one

30. Nsc-170959

31. 2-oxazolidinone, 5-((3,5-dimethylphenoxy)methyl)-

32. 5-(3,5-dimethylphenoxymethyl)-1,3-oxazolidin-2-one

33. Mls003106749

34. 1nma9j598y

35. Chebi:6797

36. 5-[(3,5-dimethylphenoxy)methyl]-2-oxazolidinone

37. Ncgc00095116-01

38. Dsstox_cid_3269

39. 2-oxazolidinone, 5-[(3,5-xylyloxy)methyl]-

40. Dsstox_rid_76949

41. Dsstox_gsid_23269

42. Metaxalona [spanish]

43. Metassalone

44. Metaxalona

45. Metaxalonum

46. Cas-1665-48-1

47. Metaxalone [usan:inn:ban]

48. Hsdb 3236

49. Sr-05000001978

50. Einecs 216-777-6

51. 5-((3,5-dimethylphenoxy)methyl)-1,3-oxazolidin-2-one

52. Brn 0884592

53. Unii-1nma9j598y

54. .meta.xalone

55. .meta.zalone

56. .meta.zolone

57. .meta.xalon

58. Metaxalone Solution

59. Skelaxin (tn)

60. Spectrum_001741

61. Metaxalone [mi]

62. Specplus_000656

63. Metaxalone (usp/inn)

64. Metaxalone [inn]

65. Spectrum2_000548

66. Spectrum3_001666

67. Spectrum4_000612

68. Spectrum5_001685

69. Metaxalone [hsdb]

70. Metaxalone [usan]

71. Metaxalone [vandf]

72. 5-(3,5-dimethylphenoxymethyl)-2-oxazolidinone

73. Metaxalone [mart.]

74. Metaxalone [usp-rs]

75. Metaxalone [who-dd]

76. Oprea1_438855

77. Schembl34908

78. Bspbio_003451

79. Kbiogr_001164

80. Kbioss_002221

81. Divk1c_006752

82. Spectrum1504229

83. Spbio_000595

84. Ahr438

85. Gtpl7609

86. Chembl1079604

87. Dtxsid3023269

88. Metaxalone [orange Book]

89. Metaxalone, >=98% (hplc)

90. Kbio1_001696

91. Kbio2_002221

92. Kbio2_004789

93. Kbio2_007357

94. Kbio3_002671

95. Hms1922h07

96. Hms2093c22

97. Metaxalone [usp Monograph]

98. Pharmakon1600-01504229

99. Bcp28377

100. Hy-b0678

101. Tox21_111428

102. Wln: T5mvotj D1or C1 E1

103. 2-oxazolidinone,5-xylyloxy)methyl]-

104. Ccg-39592

105. Nsc758703

106. S3730

107. Stl450994

108. Stl451511

109. Akos009035315

110. Tox21_111428_1

111. Db00660

112. Fs-3218

113. Nsc-758703

114. Ncgc00095116-02

115. Ncgc00095116-03

116. Ncgc00095116-05

117. Smr001821638

118. Sy052772

119. Sbi-0052859.p002

120. 2-oxazolidinone,5-dimethylphenoxy)methyl]-

121. Db-043656

122. Am20060525

123. Ft-0603568

124. M2578

125. 5-(3,5-dimethylphenoxy)methyl-2-oxazolidinone

126. C07934

127. D00773

128. Ab00053284_04

129. 665m481

130. A810747

131. J-010295

132. Q6823309

133. Sr-05000001978-1

134. Sr-05000001978-3

135. Brd-a94709349-001-02-6

136. Brd-a94709349-001-03-4

137. 5-[(3,5-dimethylphenoxy)methyl]-1,3-oxazolidin-2-one #

138. 5-{[(3,5-dimethylphenyl)oxy]methyl}-1,3-oxazolidin-2-one

139. 5-[(3,5-dimethylphenoxy)methyl]-4,5-dihydro-1,3-oxazol-2-ol

140. Metaxalone, United States Pharmacopeia (usp) Reference Standard

141. Metaxalone Solution, 1.0 Mg/ml In Methanol, Ampule Of 1 Ml, Certified Reference Material

2.4 Create Date
2005-03-26
3 Chemical and Physical Properties
Molecular Weight 221.25 g/mol
Molecular Formula C12H15NO3
XLogP32.2
Hydrogen Bond Donor Count1
Hydrogen Bond Acceptor Count3
Rotatable Bond Count3
Exact Mass221.10519334 g/mol
Monoisotopic Mass221.10519334 g/mol
Topological Polar Surface Area47.6 Ų
Heavy Atom Count16
Formal Charge0
Complexity247
Isotope Atom Count0
Defined Atom Stereocenter Count0
Undefined Atom Stereocenter Count1
Defined Bond Stereocenter Count0
Undefined Bond Stereocenter Count0
Covalently Bonded Unit Count1
4 Drug and Medication Information
4.1 Drug Information
1 of 4  
Drug NameMetaxalone
PubMed HealthMetaxalone (By mouth)
Drug ClassesSkeletal Muscle Relaxant, Centrally Acting
Drug LabelDESCRIPTION Metaxalone tablets are available as an 800 mg oval, convex pink tablet.Chemically, metaxalone is 5-[(3,5- dimethylphenoxy) methyl]-2-oxazolidinone. The empirical formula is C12H15NO3, which corresponds to a molecular weight of 221.25. The...
Active IngredientMetaxalone
Dosage FormTablet
Routeoral; Oral
Strength400mg; 800mg
Market StatusTentative Approval; Prescription
CompanyCorepharma; Amneal Pharms; Sandoz

2 of 4  
Drug NameSkelaxin
PubMed HealthMetaxalone (By mouth)
Drug ClassesSkeletal Muscle Relaxant, Centrally Acting
Drug LabelSKELAXIN (metaxalone) is available as an 800 mg oval, scored pink tablet.Chemically, metaxalone is 5-[(3,5- dimethylphenoxy) methyl]-2-oxazolidinone. The empirical formula is C12H15NO3, which corresponds to a molecular weight of 221.25. The structu...
Active IngredientMetaxalone
Dosage FormTablet
RouteOral
Strength800mg
Market StatusPrescription
CompanyKing Pharms

3 of 4  
Drug NameMetaxalone
PubMed HealthMetaxalone (By mouth)
Drug ClassesSkeletal Muscle Relaxant, Centrally Acting
Drug LabelDESCRIPTION Metaxalone tablets are available as an 800 mg oval, convex pink tablet.Chemically, metaxalone is 5-[(3,5- dimethylphenoxy) methyl]-2-oxazolidinone. The empirical formula is C12H15NO3, which corresponds to a molecular weight of 221.25. The...
Active IngredientMetaxalone
Dosage FormTablet
Routeoral; Oral
Strength400mg; 800mg
Market StatusTentative Approval; Prescription
CompanyCorepharma; Amneal Pharms; Sandoz

4 of 4  
Drug NameSkelaxin
PubMed HealthMetaxalone (By mouth)
Drug ClassesSkeletal Muscle Relaxant, Centrally Acting
Drug LabelSKELAXIN (metaxalone) is available as an 800 mg oval, scored pink tablet.Chemically, metaxalone is 5-[(3,5- dimethylphenoxy) methyl]-2-oxazolidinone. The empirical formula is C12H15NO3, which corresponds to a molecular weight of 221.25. The structu...
Active IngredientMetaxalone
Dosage FormTablet
RouteOral
Strength800mg
Market StatusPrescription
CompanyKing Pharms

4.2 Therapeutic Uses

Metaxalone is used as an adjunct to rest, physical therapy, analgesics, and other measures for the relief of discomfort associated with acute, painful musculoskeletal conditions. /Included in US product label/

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 1394


4.3 Drug Warning

The most frequent adverse effects of metaxalone are drowsiness, dizziness, headache, nervousness or irritability, nausea, vomiting, and GI upset. Other adverse effects include confusion, anorexia, dry mouth, and urinary retention. Exacerbation of tonic-clonic (grand mal) seizures has also been reported.

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 1394


Hypersensitivity reactions and rash (with or without pruritus) have occurred in patients receiving metaxalone. Anaphylactoid reactions, leukopenia, hemolytic anemia, and jaundice have occurred rarely. Abnormalities in liver function tests, such as increased serum concentrations of AST (SGOT), ALT (SGPT), alkaline phosphatase, and bilirubin, and increased sulfobromophthalein (BSP) retention and thymol turbidity, have occurred in patients receiving metaxalone. Although a causal relationship to metaxalone has not been established, nephrotoxicity and proteinuria have occurred rarely during treatment with the drug; pyuria and nephrolithiasis have also been reported.

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 1394


Safety and efficacy of metaxalone in children 12 years of age or younger have not been established; therefore, the drug should not be administered to children in this age group.

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 1394


Patients should be warned that metaxalone may impair ability to perform hazardous activities requiring mental alertness or physical coordination, such as operating machinery or driving a motor vehicle. In addition, patients should be warned that additive CNS depression may occur when the drug is administered concomitantly with other CNS depressants, including alcohol. Metaxalone should be used with caution in geriatric patients and in patients with hepatic or renal impairment. Liver function studies should be performed periodically during metaxalone therapy in patients with preexisting liver damage. The drug is contraindicated in patients with substantially impaired hepatic or renal function, known hypersensitivity to the drug or any ingredient in the formulation, or a history of drug-induced, hemolytic, or other anemias.

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 1394


For more Drug Warnings (Complete) data for METAXALONE (8 total), please visit the HSDB record page.


4.4 Drug Indication

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


FDA Label


5 Pharmacology and Biochemistry
5.1 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.


5.2 MeSH Pharmacological Classification

Neuromuscular Agents

Drugs used for their actions on skeletal muscle. Included are agents that act directly on skeletal muscle, those that alter neuromuscular transmission (NEUROMUSCULAR BLOCKING AGENTS), and drugs that act centrally as skeletal muscle relaxants (MUSCLE RELAXANTS, CENTRAL). Drugs used in the treatment of movement disorders are ANTI-DYSKINESIA AGENTS. (See all compounds classified as Neuromuscular Agents.)


5.3 FDA Pharmacological Classification
5.3.1 Active Moiety
METAXALONE
5.3.2 FDA UNII
1NMA9J598Y
5.3.3 Pharmacological Classes
Centrally-mediated Muscle Relaxation [PE]
5.4 Absorption, Distribution and Excretion

Absorption

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


Route of Elimination

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


Volume of Distribution

800 L


Clearance

68 +/- 50 L/h [Subjects received 1400mg tablet under fasted conditions]

66 +/- 51 L/h [Subjects received 2400 mg tablets under fasted conditions]


Although plasma protein binding and absolute bioavailability of metaxalone are not known, the apparent volume of distribution (V/F ~ 800 L) and lipophilicity (log P = 2.42) of metaxalone suggest that the drug is extensively distributed in the tissues. Metaxalone is metabolized by the liver and excreted in the urine as unidentified metabolites.

US Natl Inst Health; DailyMed. Current Medication Information for Skelaxin (metaxalone) tablet (June 2007). Available from, as of October 15, 2010: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=4505


Peak plasma concentrations of metaxalone occur approximately 3 hours after a 400 mg oral dose under fasted conditions. Thereafter, metaxalone concentrations decline log-linearly with a terminal half-life of 9.0 + or - 4.8 hours. Doubling the dose of skelaxin from 400 mg to 800 mg results in a roughly proportional increase in metaxalone exposure as indicated by peak plasma concentrations (Cmax) and area under the curve (AUC). Dose proportionality at doses above 800 mg has not been studied. The absolute bioavailability of metaxalone is not known

US Natl Inst Health; DailyMed. Current Medication Information for Skelaxin (metaxalone) tablet (June 2007). Available from, as of October 15, 2010: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=4505


5.5 Metabolism/Metabolites

Probably hepatic.


Biotransformations...studied in dogs and in man. 5-(3-methyl-5-carboxyphenoxymethyl)-2-oxazolidinone, major metabolite, is excreted in urine and feces; this also occurs in urine as ester glucuronide. Fission of ether linkage...affords...3,5-xylenol and 5-hydroxymethyloxazolidinone. Oxazolidinone ring is stable in mammals.

The Chemical Society. Foreign Compound Metabolism in Mammals. Volume 1: A Review of the Literature Published Between 1960 and 1969. London: The Chemical Society, 1970., p. 175


Yields 5-(5-carboxy-3-methylphenoxymethyl)-2-oxazolidone in man & in dogs, yields 3,5-dimethylphenol in man and in dogs. /From table/

Goodwin, B.L. Handbook of Intermediary Metabolism of Aromatic Compounds. New York: Wiley, 1976., p. D-93


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

US Natl Inst Health; DailyMed. Current Medication Information for Skelaxin (metaxalone) tablet (June 2007). Available from, as of October 15, 2010: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=4505


5.6 Biological Half-Life

9.2 (+/- 4.8) hours


Terminal half-life /is/ 9.0 + or - 4.8 hours

US Natl Inst Health; DailyMed. Current Medication Information for Skelaxin (metaxalone) tablet (June 2007). Available from, as of October 15, 2010: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=4505


5.7 Mechanism of Action

The mechanism of action of metaxalone in humans has not been established, but may be due to general central nervous system depression.


Metaxalone is a CNS depressant that has sedative and skeletal muscle relaxant effects. The precise mechanism of action of the drug is not known. The skeletal muscle relaxant effects of orally administered metaxalone are minimal and are probably related to its sedative effect. The drug does not directly relax skeletal muscle and, unlike neuromuscular blocking agents, does not depress neuronal conduction, neuromuscular transmission, or muscle excitability.

American Society of Health System Pharmacists; AHFS Drug Information 2010. Bethesda, MD. (2010), p. 1395


The mechanism of action of metaxalone in humans has not been established, but may be due to general central nervous system depression. Metaxalone has no direct action on the contractile mechanism of striated muscle, the motor end plate or the nerve fiber.

US Natl Inst Health; DailyMed. Current Medication Information for Skelaxin (metaxalone) tablet (June 2007). Available from, as of October 15, 2010: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=4505