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 of the major metabolites are unhydrolyzed carbamates. Methocarbamol is marketed under different names when presented in combination with other active ingredients...