Methocarbamol

Methocarbamol is a central muscle relaxant used to treat skeletal muscle spasms. Under the trade name Robax, it is marketed by Actient Pharmaceuticals in the United States and Pfizer in Canada. The mechanism of action of methocarbamol is currently unknown, but may involve the inhibition of carbonic anhydrase. The muscle relaxant effects of methocarbamol are largely attributed to central depressant effects; however, peripheral effects of methocarbamol to prolong muscle refractory period have also been reported.

Metabolism

Methocarbamol is the carbamate of guaifenesin, but does not produce guaifenesin as a metabolite, because 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.

Marketing

Methocarbamol is marketed under different names when presented in combination with other active ingredients. In combination with acetaminophen (Paracetamol), under trade names Robaxacet and Tylenol Body Pain Night, whereas Robax Platinum is the trade name for a formulation of methocarbamol and ibuprofen. A combination of methocarbamol and aspirin is marketed as Robaxisal, however in Spain the tradename Robaxisal is used for the Paracetamol combination instead of Robaxacet.