Wikipedia

Methocarbamol

Methocarbamol,sold under the brand nameRobaxinamong others, is a medication used for short-termmusculoskeletalpain.[3][4]It may be used together with rest, physical therapy, andpain medication.[3][5][6]It is less preferred inlow back pain.[3]It has limited use forrheumatoid arthritisandcerebral palsy.[3][7]Effects generally begin within half an hour.[3]It is taken by mouth orinjection into a vein.[3]

Methocarbamol
Clinical data
Trade namesRobaxin, Marbaxin, others
AHFS/Drugs.comMonograph
MedlinePlusa682579
License data
Pregnancy
category
  • AU:B2
Routes of
administration		By mouth,intravenous
ATC code
Legal status
Legal status
Pharmacokineticdata
MetabolismLiver
Eliminationhalf-life1.14–1.24 hours[2]
Identifiers
  • (RS)-2-hydroxy-3-(2-methoxyphenoxy)propyl carbamate
CAS Number
PubChemCID
IUPHAR/BPS
DrugBank
ChemSpider
UNII
KEGG
ChEBI
ChEMBL
CompTox Dashboard(EPA)
ECHA InfoCard100.007.751Edit this at Wikidata
Chemical and physical data
FormulaC11H15NO5
Molar mass241.243g·mol−1
3D model (JSmol)
  • O=C(OCC(O)COc1ccccc1OC)N
  • InChI=1S/C11H15NO5/c1-15-9-4-2-3-5-10(9)16-6-8(13)7-17-11(12)14/h2-5,8,13H,6-7H2,1H3,(H2,12,14)checkY
  • Key:GNXFOGHNGIVQEH-UHFFFAOYSA-NcheckY
☒NcheckY(what is this?)(verify)

Common side effects include headaches, sleepiness, and dizziness.[3][8]Serious side effects may includeanaphylaxis,liver problems, confusion, andseizures.[4]Use is not recommended inpregnancyandbreastfeeding.[3][4]Because of the risk of injury, skeletal muscle relaxants should generally be avoided in geriatric patients.[3]Methocarbamol is a centrally actingmuscle relaxant.[3]How it works is unclear, but it does not appear to affect muscles directly.[3]

Methocarbamol was developed in 1956 in the laboratories ofA. H. Robins(later acquired byPfizer). Studies were directed towards the development ofpropanediolderivatives which possessed muscle relaxant properties superior to those ofmephenesin,which had low potency and a short duration of action.[9]It was approved for medical use in the United States in 1957.[3]It is available as ageneric medication.[3][4]In 2022, it was the 126th most commonly prescribed medication in the United States, with more than 5million prescriptions.[10][11]Methocarbamol is available in afixed-dose combinationwith ibuprofen asmethocarbamol/ibuprofen(sold under the brand name (Summit Ultra).[12]

Medical use

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Methocarbamol is a muscle relaxant used to treat acute, painful musculoskeletal spasms in a variety of musculoskeletal conditions.[13]However, there is limited and inconsistent published research on the medication's efficacy and safety in treating musculoskeletal conditions, primarily neck and back pain.[13]

Methocarbamol injection may have a beneficial effect in the control of the neuromuscular spasms oftetanus.[6]It does not, however, replace the current treatment regimen.[6]

It is not useful in chronic neurological disorders, such ascerebral palsyor otherdyskinesias.[3]

Currently, there is some suggestion that muscle relaxants may improve the symptoms ofrheumatoid arthritis;however, there is insufficient data to prove its effectiveness or to answer concerns regarding optimal dosing, choice of muscle relaxant, adverse effects, and functional status.[7]

Comparison to similar agents

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The clinical effectiveness of methocarbamol compared to other muscle relaxants is not well known.[13]One trial of methocarbamol versuscyclobenzaprine,a well-studied muscle relaxant, in those with localized muscle spasm found there were no significant differences in their effects on muscle spasm, limitation of motion, or limitation of daily activities.[13]

Contraindications

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Contraindications for methocarbamol include:

Side effects

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Methocarbamol is a centrally acting skeletal muscle relaxant that has significant potential adverse effects, especially on the central nervous system.[3]

Potential side effects of methocarbamol include:

  • Most commonly drowsiness, blurred vision, headache, nausea, and skin rash.[8]
  • Possible clumsiness (ataxia), upset stomach, flushing, mood changes, trouble urinating, itchiness, and fever.[14][15]
  • Bothtachycardia(fast heart rate) andbradycardia(slow heart rate) have been reported.[15]
  • Hypersensitivity reactions andanaphylaticreactions are also reported.[5][6]
  • May cause respiratory depression when combined withbenzodiazepines,barbiturates,codeine,or other muscle relaxants.[16]
  • May cause urine to turn black, blue, or green.[14]

While the product label states that methocarbamol can causejaundice,there is minimal evidence to suggest that methocarbamol causes liver damage.[8]During clinical trials of methocarbamol, there were no laboratory measurements of liver damage indicators, such as serumtransaminase(AST/ALT) levels, to confirmhepatotoxicity.[8]Although unlikely, it is impossible to rule out that methocarbamol may cause mild liver injury with use.[8]

Elderly

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Skeletal muscle relaxants are associated with an increased risk of injury among older adults.[17]Methocarbamol appeared to be less sedating than other muscle relaxants, most notablycyclobenzaprinebut had a similarly increased risk of injury.[16][17]Methocarbamol is cited along with "most muscle relaxants" in the 2012Beers Criteriaas being "poorly tolerated by older adults, because of anticholinergic adverse effects, sedation, increased risk of fractures," noting that "effectiveness dosages tolerated by older adults is questionable."[18]

Pregnancy

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Methocarbamol is labeled by the FDA as apregnancy categoryC medication.[6]Theteratogeniceffects of the medication are not known and should be given to pregnant women only when indicated.[6]

Overdose

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There is limited information available on the acute toxicity of methocarbamol.[5][6]Overdose is observed frequently in conjunction with CNS depressants such asalcoholorbenzodiazepinesand will have symptoms of nausea, drowsiness, blurred vision,hypotension,seizures, and coma.[6]There are reported deaths with an overdose of methocarbamol alone or in the presence of other CNS depressants.[5][6]

Abuse

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Unlike other carbamates such asmeprobamateand its prodrugcarisoprodol,methocarbamol has greatly reduced abuse potential.[19]Studies comparing it to the benzodiazepinelorazepamand the antihistaminediphenhydramine,along with placebo, find that methocarbamol produces increased "liking" responses and some sedative-like effects; however, at higher dosesdysphoriais reported.[19]It is considered to have an abuse profile similar to, but weaker than,lorazepam.[19]

Interactions

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Methocarbamol may inhibit the effects ofpyridostigmine bromide.[5][6]Therefore, methocarbamol should be used with caution in those withmyasthenia gravistakinganticholinesterasemedications.[6]

Methocarbamol may disrupt certain screening tests as it can cause color interference in laboratory tests for5-hydroxy-indoleacetic acid (5-HIAA)and in urinary testing forvanillylmandelic acid (VMA)using the Gitlow method.[6]

Pharmacology

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Mechanism of action

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The mechanism of action of methocarbamol has not currently been established.[3]Its effect is thought to be localized to the central nervous system rather than a direct effect on skeletal muscles.[3]It does not affect the motor end plate or the peripheral nerve fiber.[6]The efficacy of the medication is likely related to its sedative effect.[3]Alternatively, methocarbamol may act via inhibition of acetylcholinesterase, similarly tocarbamate.[20]

Pharmacokinetics

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In healthy individuals, the plasma clearance of methocarbamol ranges between 0.20 and 0.80 L/h/kg.[6]The mean plasma elimination half-life ranges between 1 and 2 hours, and the plasma protein binding ranges between 46% and 50%.[6]The elimination half-life was longer in the elderly, those withkidneyproblems, and those withliverproblems.[6]

Metabolism

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Methocarbamol is thecarbamatederivative ofguaifenesin,but does not produce guaifenesin as ametabolite,because the carbamate bond is not hydrolyzed metabolically;[8][6]its metabolism is by Phase I ring hydroxylation andO-demethylation, followed by Phase II conjugation.[6]All the major metabolites are unhydrolyzed carbamates.[21][22]Small amounts of unchanged methocarbamol are also excreted in the urine.[5][6]

Society and culture

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Methocarbamol was approved as a muscle relaxant for acute, painful musculoskeletal conditions in the United States in 1957.[8]Muscle relaxants are widely used to treat low back pain, one of the most frequent health problems in industrialized countries. Currently, there are more than 3 million prescriptions filled yearly.[8]Methocarbamol andorphenadrineare each used in more than 250,000 U.S. emergency department visits for lower back pain each year.[23]In the United States, low back pain is the fifth most common reason for all physician visits and the second most common symptomatic reason.[24]In 80% of primary care visits for low back pain, at least one medication was prescribed at the initial office visit and more than one third were prescribed two or more medications.[25]The most commonly prescribed drugs for low back pain included skeletal muscle relaxants.[26]Cyclobenzaprineand methocarbamol are on the U.S.Medicareformulary, which may account for the higher use of these products.[17]

Economics

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It is relatively inexpensive as of 2016.[27]The generic formulation of the medication is relatively inexpensive, costing less than the alternativemetaxalonein 2016.[28][27]

Marketing

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Generic methocarbamol 750mg tablet.

Methocarbamol without other ingredients is sold under the brand name Robaxin in the U.K., U.S., Canada[29]and South Africa; it is marketed as Lumirelax in France, Ortoton in Germany and many other names worldwide.[30]In combination with other active ingredients it is sold under other names: withacetaminophen(paracetamol), under trade names Robaxacet and Tylenol Body Pain Night; withibuprofenas Robax Platinum; withacetylsalicylic acidas Robaxisal in the U.S. and Canada.[31][32]However, in Spain the tradename Robaxisal is used for the paracetamol combination instead of Robaxacet.[citation needed]These combinations are also available from independent manufacturers under generic names.[citation needed]

Research

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Althoughopioidsare typically first-line treatments in severe pain, several trials suggest that methocarbamol may improve recovery and decrease hospital length of stay in those with muscle spasms associated withrib fractures.[33][34][35]However, methocarbamol was less useful in the treatment of acute traumatic pain in general.[36]

Long-term studies evaluating the risk of development of cancer in using methocarbamol have not been performed.[5][6]There are currently no studies evaluating the effect of methocarbamol on mutagenesis or fertility.[5][6]

The safety and efficacy of methocarbamol have not been established in pediatric individuals below the age of 16 except intetanus.[5][6]

References

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  1. ^"Robaxin-750 - Summary of Product Characteristics (SmPC)".(emc).8 August 2017.Retrieved19 April2020.
  2. ^Sica DA, Comstock TJ, Davis J, Manning L, Powell R, Melikian A, et al. (1990). "Pharmacokinetics and protein binding of methocarbamol in renal insufficiency and normals".European Journal of Clinical Pharmacology.39(2):193–194.doi:10.1007/BF00280060.PMID2253675.S2CID626920.
  3. ^abcdefghijklmnopqr"Methocarbamol Monograph for Professionals".Drugs.com.American Society of Health-System Pharmacists.
  4. ^abcdBritish national formulary: BNF 76(76 ed.). Pharmaceutical Press. 2018. p. 1093.ISBN9780857113382.
  5. ^abcdefghi"Robaxin- methocarbamol tablet, film coated".DailyMed.18 July 2019.Retrieved19 April2020.
  6. ^abcdefghijklmnopqrstuvwx"Robaxin- methocarbamol injection".DailyMed.10 December 2018.Retrieved19 April2020.
  7. ^abRichards BL, Whittle SL, Buchbinder R (January 2012)."Muscle relaxants for pain management in rheumatoid arthritis".The Cochrane Database of Systematic Reviews.1:CD008922.doi:10.1002/14651858.CD008922.pub2.PMC11702505.PMID22258993.S2CID73769165.
  8. ^abcdefgh"Methocarbamol".LiverTox: Clinical and Research Information on Drug-Induced Liver Injury.National Institute of Diabetes and Digestive and Kidney Diseases. 30 January 2017.PMID31643609.
  9. ^Analytical Profiles of Drug Substances and Excipients, pp. 373
  10. ^"The Top 300 of 2022".ClinCalc.Archivedfrom the original on 30 August 2024.Retrieved30 August2024.
  11. ^"Methocarbamol Drug Usage Statistics, United States, 2013 - 2022".ClinCalc.Retrieved30 August2024.
  12. ^"Summit Ultra Product information".Health Canada.2 August 2018.Retrieved17 February2025.
  13. ^abcdChou R, Peterson K, Helfand M (August 2004)."Comparative efficacy and safety of skeletal muscle relaxants for spasticity and musculoskeletal conditions: a systematic review".Journal of Pain and Symptom Management.28(2):140–175.doi:10.1016/j.jpainsymman.2004.05.002.PMID15276195.
  14. ^ab"Methocarbamol".MedlinePlus.Retrieved18 April2020.
  15. ^ab"Methocarbamol Side Effects: Common, Severe, Long Term".Drugs.com.Retrieved18 April2020.
  16. ^abSee S, Ginzburg R (August 2008). "Choosing a skeletal muscle relaxant".American Family Physician.78(3):365–370.PMID18711953.
  17. ^abcSpence MM, Shin PJ, Lee EA, Gibbs NE (July 2013). "Risk of injury associated with skeletal muscle relaxant use in older adults".The Annals of Pharmacotherapy.47(7–8):993–998.doi:10.1345/aph.1R735.PMID23821610.S2CID9037478.
  18. ^"Beers Criteria Medication List".DCRI.Archived fromthe originalon 7 November 2020.Retrieved18 October2020.
  19. ^abcPreston KL, Wolf B, Guarino JJ, Griffiths RR (August 1992). "Subjective and behavioral effects of diphenhydramine, lorazepam and methocarbamol: evaluation of abuse liability".The Journal of Pharmacology and Experimental Therapeutics.262(2):707–720.PMID1501118.
  20. ^"Methocarbamol".PubChem.U.S. National Library of Medicine.Retrieved6 July2020.
  21. ^Methocarbamol. In:DRUGDEX System[intranet database]. Greenwood Village, Colorado: Thomson Healthcare; c1974–2009 [cited 2009 Feb 10].
  22. ^Bruce RB, Turnbull LB, Newman JH (January 1971). "Metabolism of methocarbamol in the rat, dog, and human".Journal of Pharmaceutical Sciences.60(1):104–106.doi:10.1002/jps.2600600120.PMID5548215.
  23. ^Friedman BW, Cisewski D, Irizarry E, Davitt M, Solorzano C, Nassery A, et al. (March 2018)."A Randomized, Double-Blind, Placebo-Controlled Trial of Naproxen With or Without Orphenadrine or Methocarbamol for Acute Low Back Pain".Annals of Emergency Medicine.71(3): 348–356.e5.doi:10.1016/j.annemergmed.2017.09.031.PMC5820149.PMID29089169.
  24. ^Chou R, Huffman LH (October 2007). "Medications for acute and chronic low back pain: a review of the evidence for an American Pain Society/American College of Physicians clinical practice guideline".Annals of Internal Medicine.147(7):505–514.doi:10.7326/0003-4819-147-7-200710020-00008.PMID17909211.S2CID32719708.
  25. ^Cherkin DC, Wheeler KJ, Barlow W, Deyo RA (March 1998). "Medication use for low back pain in primary care".Spine.23(5):607–614.doi:10.1097/00007632-199803010-00015.PMID9530793.S2CID23664539.
  26. ^Luo X, Pietrobon R, Curtis LH, Hey LA (December 2004). "Prescription of nonsteroidal anti-inflammatory drugs and muscle relaxants for back pain in the United States".Spine.29(23):E531 –E537.doi:10.1097/01.brs.0000146453.76528.7c.PMID15564901.S2CID72742439.
  27. ^abFine PG (2016).The Hospice Companion: Best Practices for Interdisciplinary Care of Advanced Illness.Oxford University Press. p. PT146.ISBN978-0-19-045692-4.
  28. ^Robbins LD (2013).Management of Headache and Headache Medications.Springer Science & Business Media. p. PT147.ISBN978-1-4612-2124-1.
  29. ^"ROBAXIN product appearance in Canada".ctchealth.ca.13 July 2021.Retrieved13 December2021.
  30. ^"Methocarbamol".Drugs.com.Retrieved12 May2018.
  31. ^"New Drugs and Indications Reviewed at the May 2003 DEC Meeting"(PDF).ESI Canada.Archived fromthe original(PDF)on 10 July 2011.Retrieved14 November2008.
  32. ^"Tylenol Body Pain Night Overview and Dosage".Tylenol Canada.Archived fromthe original(website)on 31 March 2012.Retrieved23 April2012.
  33. ^Patanwala AE, Aljuhani O, Kopp BJ, Erstad BL (October 2017). "Methocarbamol use is associated with decreased hospital length of stay in trauma patients with closed rib fractures".American Journal of Surgery.214(4):738–742.doi:10.1016/j.amjsurg.2017.01.003.PMID28088301.
  34. ^Deloney L, Smith M, Carter C, Privette A, Leon S, Eriksson E (January 2020)."946: Methocarbamol reduces opioid use and length of stay in young adults with traumatic rib fractures".Critical Care Medicine.48(1): 452.doi:10.1097/01.ccm.0000633320.62811.06.ISSN0090-3493.
  35. ^Smith M, Deloney L, Carter C, Leon S, Privette A, Eriksson E (January 2020)."1759: Use of methocarbamol in geriatric patients with rib fractures is associated with improved outcomes".Critical Care Medicine.48(1): 854.doi:10.1097/01.ccm.0000649332.10326.98.ISSN0090-3493.
  36. ^Aljuhani O, Kopp BJ, Patanwala AE (2017). "Effect of Methocarbamol on Acute Pain After Traumatic Injury".American Journal of Therapeutics.24(2):e202 –e206.doi:10.1097/mjt.0000000000000364.PMID26469684.S2CID24284482.
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