Methocarbamol

Methocarbamol

Systematic (IUPAC) name
2-hydroxy-3-(2-methoxyphenoxy)propyl carbamate
Clinical data
AHFS/Drugs.com	monograph
MedlinePlus	a682579
Pregnancy cat.	C
Legal status	℞-only (US) OTC(Canada)
Routes	Oral, intravenous
Pharmacokinetic data
Metabolism	Hepatic
Half-life	1.14–1.24 hours[1]
Identifiers
CAS number	532-03-6 Y
ATC code	M03BA03
PubChem	CID 4107
DrugBank	APRD01102
ChemSpider	3964 Y
UNII	125OD7737X Y
KEGG	D00402 Y
ChEMBL	CHEMBL1201117 N
Chemical data
Formula	C11H15NO5
Mol. mass	241.241 g/mol
SMILES	eMolecules & PubChem
InChI 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) Y Key:GNXFOGHNGIVQEH-UHFFFAOYSA-N Y
N(what is this?)  (verify)

Methocarbamol (trade name Robaxin, which is marketed by Actient Pharmaceuticals LLC in the United States and Pfizer in Canada) is a central muscle relaxant used to treat skeletal muscle spasms. It is the carbamate of guaifenesin, but does not produce guaifenesin as a metabolite, since the carbamate bond is not hydrolyzed metabolically; metabolism is by Phase I ring hydroxylation and O-demethylation, followed by Phase II conjugation. All the major metabolites are unhydrolyzed carbamates.^[2][3]

Generic Methocarbamol 750mg Oral Tablet.

Methocarbamol is marketed under different names when presented in combination with other active ingredients. In combination with acetaminophen (Paracetamol), its trade name is Robaxacet, whereas Robax Platinum is the trade name for a formulation of methocarbamol and ibuprofen.^[4] A combination of methocarbamol and aspirin is marketed as Robaxisal. Unlike other carbamates such as carisoprodol and meprobamate, Methocarbamol has greatly reduced abuse potential. Studies comparing it to lorazepam (Ativan) and diphenhydramine (Benadryl), along with placebo, find that methocarbamol produces increased 'liking' responses and some sedative-like effects, however, at higher doses dysphoria is reported. It is considered to have an abuse profile similar to, but weaker than, lorazepam. ^[5]

Potential side-effects include: drowsiness, dizziness, upset stomach, flushing, blurred vision, and fever. Serious side-effects include the development of a severe skin rash or itching, slow heart rate, fainting, jaundice, persistent nausea/vomiting, stomach/abdominal pain, mental/mood changes, clumsiness, trouble urinating, signs of infection. ^[6] In addition, methocarbamol may cause urine to turn black, blue, or green. However, this effect is harmless.^[7]

Because of potential for side-effects, this drug is on the list for High-Risk Medications in the elderly. (See NCQA’s HEDIS Measure: Use of High Risk Medications in the Elderly, http://www.ncqa.org/Portals/0/Newsroom/SOHC/Drugs_Avoided_Elderly.pdf).

Chemistry

Methocarbamol, 3-(2-methoxyphenoxy)-1,2-propanediol-1 carbamate, is synthesized by successive reaction with phosgene and then ammonia into 3-(2-methoxyphenoxy)propane-1,2-diol.

• R.S. Murphey, U.S. Patent 2,770,649 (1956).
• Yale, H. L.; Pribyl, E. J.; Braker, W.; Bergeim, F. H.; Lott, W. A. (1950). Journal of the American Chemical Society 72 (8): 3710. doi:10.1021/ja01164a107.  edit

References

1. ^ Sica DA, Comstock TJ, Davis J, Manning L, Powell R, Melikian A, Wright G. (1990). "Pharmacokinetics and protein binding of methocarbamol in renal insufficiency and normals". European Journal of Clinical Pharmacology 39 (2): 193–4. doi:10.1007/BF00280060. PMID 2253675. 
2. ^ Methocarbamol. In: DRUGDEX System [intranet database]. Greenwood Village, Colorado: Thomson Healthcare; c1974–2009 [cited 2009 Feb 10].
3. ^ Bruce RB, Turnbull LB, Newman JH. (1971 Jan). "Metabolism of methocarbamol in the rat, dog, and human". J Pharm Sci 60 (1): 104–106. doi:10.1002/jps.2600600120. PMID 5548215. 
4. ^ "New Drugs and Indications Reviewed at the May 2003 DEC Meeting" (PDF). ESI Canada. http://www.esi-canada.com/aboutus/news/health_newsflashes/volume5_issue9_newdrugsmay2003.pdf. Retrieved 2008-11-14. 
5. ^ "Subjective and behavioral effects of diphenhydramine, lorazepam and methocarbamol: evaluation of abuse liability". Journal of Pharmacology and Experimental Therapeutics. http://www.ncbi.nlm.nih.gov/pubmed/1501118. Retrieved 2011-05-06. 
6. ^ METHOCARBAMOL – ORAL (Robaxin) side effects, medical uses, and drug interactions. Medicinenet.com. Retrieved on 2011-11-09.
7. ^ Methocarbamol: MedlinePlus Drug Information. Nlm.nih.gov. Retrieved on 2011-11-09.