- Adverse effects
- Food Interactions
Methocarbamol was developed in the early 1950s as a treatment for muscle spasticity and the associated pain.[
Methocarbamol was developed in the early 1950s as a treatment for muscle spasticity and the associated pain.[6,7] It is a guaiacol glyceryl ether.
Methocarbamol tablets and intramuscular injections are prescription medicines indicated in the United States as an adjunct to rest, physical therapy, and other measures for the relief of discomforts associated with acute, painful musculoskeletal conditions.[Label,9] In Canada, methocarbamol can be sold as an over the counter oral medicine at a lower dose that may be combined with [acetaminophen] or [ibuprofen]. A combination product with [acetylsalicylic acid] and [codeine] is available in Canada by prescription.
Methocarbamol was FDA approved on 16 July 1957.
Methocarbamol tablets and intramuscular injections are indicated in the United States as an adjunct...
Methocarbamol tablets and intramuscular injections are indicated in the United States as an adjunct to rest, physical therapy, and other measures for the relief of discomforts associated with acute, painful musculoskeletal conditions.[Label,9] Oral methocarbamol in America may be given up to 1500mg 4 times daily for 2-3 days.
In Canada, methocarbamol containing oral formulations are sold over the counter for pain associated with muscle spasm. However, if these combination formulations include codeine, they are prescription only. Read more
Methacarbamol is a skeletal muscle relaxant with an unknown mechanism of action.[ Methacarbamol is a skeletal muscle relaxant with an unknown mechanism of action. Methacarbamol has been shown to block spinal polysynaptic reflexes, decrease nerve transmission in spinal and supraspinal polysynaptic pathways, and prolong the refractory period of muscle cells.[5,4] Methocarbamol does not act as a local anesthetic upon injection. In animal studies, methocarbamol also prevents convulsions after electric shock. Read more
Mechanism of action
The mechanism of action of methocarbamol is thought to be dependant on its central nervous system de... The mechanism of action of methocarbamol is thought to be dependant on its central nervous system depressant activity. This action may be mediated through blocking spinal polysynaptic reflexes, decreasing nerve transmission in spinal and supraspinal polysynaptic pathways, and prolonging the refractory period of muscle cells.[5,4] Methocarbamol has been found to have no effect on contraction of muscle fibres, motor end plates, or nerve fibres. Read more
The time to maximum concentration is 1.1 hours for both healthy patients and those on hemodialysis.[...
The time to maximum concentration is 1.1 hours for both healthy patients and those on hemodialysis. The maximum plasma concentration is 21.3mg/L for healthy patients and 28.7mg/L in hemodialysis patients. The area under the curve for healthy patients is 52.5mg/L\*hr and 87.1mg/L*hr in hemodialysis patients. AUC% based on terminal elimination half life is 2% for healthy patients and 4% for hemodialysis patients.
Older studies report maximum plasma concentrations in 0.5 hours. Read more
Methocarbamol is 46-50% protein bound in healthy patients and 47.3-48.9% protein bound in hemodialys... Methocarbamol is 46-50% protein bound in healthy patients and 47.3-48.9% protein bound in hemodialysis patients. Read more
Volume of distribution
Volume of distribution data in humans is scarce. In horses, the volume of distribution is 515-942mL/... Volume of distribution data in humans is scarce. In horses, the volume of distribution is 515-942mL/kg at steady state or 724-1130mL/kg. Read more
The elimination half life is 1.14 hours in healthy subjects and 1.24 hours in subjects with renal in... The elimination half life is 1.14 hours in healthy subjects and 1.24 hours in subjects with renal insufficiency. Older studies report half lives of 1.6-2.15 hours. Read more
Route of elimination
In humans the majority of the dose is eliminated in the urine.[ In humans the majority of the dose is eliminated in the urine. In dogs, 88.85% of the dose is eliminated in urine and 2.14% in the feces. In rats, 84.5-92.5% of the dose is eliminated in the urine and 0-13.3% is eliminated in the feces. Read more
Overdose of methocarbamol may be associated with alcohol and other central nervous system depressant...
Overdose of methocarbamol may be associated with alcohol and other central nervous system depressants.[Label] Patients may experience nausea, drowsiness, blurred vision, hypotension, seizures, and coma.[Label] Treatment of overdose is generally through airway maintenance, monitoring urinary output, vital signs, and giving fluid intravenously if necessary.[Label]
The oral LD50 in rats is 3576.2mg/kg.
The FDA has classified methocarbamol as pregnancy category C.[Label] Animal and human studies have not been performed to determine the risks to a fetus, however fetal and congenital abnormalities have been reported.[Label] Methocarbamol is excreted in the milk of dogs, however it is unknown if this is also the case for humans.[Label] Caution should be exercised when taking methocarbamol while breastfeeding.[Label]
Studies to assess the carcinogenicity, mutagenicity, or effects on fertility of methocarbamol have not been performed.[Label] Read more
|Effect||Regions||Age Groups||Incidences||Evidence Type|
|Mild muscular incoordination||US||
- Avoid alcohol.
- Take without regard to meals.
- 1 . Sica DA, Comstock TJ, Davis J, Manning L, Powell R, Melikian A, Wright G: Pharmacokinetics and protein binding of methocarbamol in renal insufficiency and normals. Eur J Clin Pharmacol. 1990;39(2):193-4. [PubMed: 2253675]
- 2 . Bruce RB, Turnbull LB, Newman JH: Metabolism of methocarbamol in the rat, dog, and human. J Pharm Sci. 1971 Jan;60(1):104-6. [PubMed: 5548215]
- 3 . Witenko C, Moorman-Li R, Motycka C, Duane K, Hincapie-Castillo J, Leonard P, Valaer C: Considerations for the appropriate use of skeletal muscle relaxants for the management of acute low back pain. P T. 2014 Jun;39(6):427-35. [PubMed: 25050056]
- 4 . Crankshaw DP, Raper C: Mephenesin, methocarbamol, chlordiazepoxide and diazepam: actions on spinal reflexes and ventral root potentials. Br J Pharmacol. 1970 Jan;38(1):148-56. doi: 10.1111/j.1476-5381.1970.tb10343.x. [PubMed: 5413283]
- 5 . Muir WW 3rd, Sams RA, Ashcraft S: The pharmacology and pharmacokinetics of high-dose methocarbamol in horses. Equine Vet J Suppl. 1992 Feb;(11):41-4. [PubMed: 9109959]
- 6 . Authors unspecified: Methocarbamol-A New Lissive Agent. Can Med Assoc J. 1958 Dec 15;79(12):1008-9. [PubMed: 20325834]
- 7 . O'DOHERTY DS, SHIELDS CD: Methocarbamol; new agent in treatment of neurological and neuromuscular diseases. J Am Med Assoc. 1958 May 10;167(2):160-3. [PubMed: 13538683]
- 8 . FDA Approved Drug Products: Robaxin [Link]
- 9 . FDA Approved Drug Products: Robaxin Intramuscular Injection [Link]
- 10 . Pfizer Canada: Robax [Link]