Methocarbamol

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Cat Number

API532036

CAS Number

532-03-6

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Product Detail Description Scientific Support Customer Q&A

CAS Number

532-03-6

EINECS

208-524-3

Storage

Store at room temperature

Synonyms

Robaxin; Metocarbamol; Miolaxene; Relestrid; Surquetil; Tresortil; Delaxin; Etroflex

Molecular Formula

C11H15NO5

Molecular Weight

241.24

Smiles

COC1=CC=CC=C1OCC(COC(=O)N)O

Appearance

White to almost white powder to crystal

Melting Point

94-97°C

Boiling Point

472.5±40.0°C at 760 mmHg

Relative Density

1.3±0.1

General Description

Methocarbamol is a centrally acting muscle relaxant with a carbamate structure linked to a guaiacol ether backbone. It is chemically related to mephenesin but incorporates a 2‑hydroxy‑3‑(o‑methoxyphenoxy)propyl group that reduces the risk of hemolysis and extends the duration of action.

Mechanism of Action

The exact mechanism remains incompletely defined, but methocarbamol is thought to depress polysynaptic reflexes in the spinal cord and subcortical areas of the brain. It does not alter the action potential of nerve or muscle fibers nor does it interfere with acetylcholine release. The drug may produce its effects through general central nervous system depression, with potential GABAergic modulation, although no direct GABA receptor binding has been demonstrated.

Application

Methocarbamol is indicated as an adjunct to rest, physical therapy, and other measures for the relief of acute, painful musculoskeletal conditions such as muscle strains, sprains, and spasms. It is not effective for cerebral palsy or other chronic spastic states. The drug has a low incidence of sedation compared to other centrally acting muscle relaxants, though it can still cause drowsiness, dizziness, and gastrointestinal upset.

In a randomized, double‑blind trial, 240 emergency department patients with acute nonradicular low back pain received naproxen plus either placebo, orphenadrine, or methocarbamol for one week. The primary outcome was improvement in Roland‑Morris Disability Questionnaire score from discharge to one week. All three groups improved substantially, but none of the between‑group differences exceeded the threshold for clinical significance. Adverse events were similar across arms. Adding a muscle relaxant to naproxen did not enhance functional recovery beyond naproxen alone.

Fig. 1 CONSORT flow diagram. (Friedman BW, et al., 2018)

References

Friedman BW, et al. A Randomized, Double-Blind, Placebo-Controlled Trial of Naproxen With or Without Orphenadrine or Methocarbamol for Acute Low Back Pain. Ann Emerg Med. 2018;71(3):348-356.e5.

Does Methocarbamol require protection from light during storage?

Yes, it is moderately photosensitive. Prolonged light exposure can cause discoloration and degradation. Store in light-resistant, tightly sealed containers.

What is the recommended storage temperature for Methocarbamol?

Store at controlled room temperature (15-25°C). Avoid excessive heat above 30°C, which can soften the powder and accelerate hydrolysis of the carbamate groups.

Is Methocarbamol stable in solution for injectable formulations?

Aqueous solutions are stable at pH 4-6 when protected from light.

How is the impurity 3-(2-methoxyphenoxy)-1,2-propanediol monitored during stability?

This hydrolysis product is quantified using a validated HPLC method, ensuring it remains below USP limits.