Methocarbamol-d5 is intended for use as an internal standard for the quantification of methocarbamol by GC- or LC-MS. Methocarbamol is an orally bioavailable skeletal muscle relaxant.1 In vivo, methocarbamol inhibits the ability of mice to remain on a vertical ladder for 1 minute (ED50 = 15 mg/kg) and decreases forelimb grip strength by 35.9% when administered at a dose of 500 mg/kg.1,2 It abolishes femoral nerve-stimulated polysynaptic reflex contractions of the cat tibialis anterior muscle and prolongs the mean refractory period of directly or indirectly stimulated skeletal muscle when administered at a dose of 200 mg/kg.3 Methocarbamol also selectively inhibits human carbonic anhydrase (CA) isoform I over CAII (IC50s = 70 and ~80,000 μM, respectively).4 Formulations containing methocarbamol have been used to treat skeletal muscle spasms.
1.Cymbalist, M.A., and Shapero, M.A comparative study of the effect of some centrally acting skeletal muscle relaxants in miceJ. Pharm. Pharmacol.26(2)109-112(1974) 2.Nevins, M.E., Nash, S.A., and Beardsley, P.M.Quantitative grip strength assessment as a means of evaluating muscle relaxation in micePsychopharmacology (Berl)110(1-2)92-86(1993) 3.Crankshaw, D.P., and Raper, C.Some studies on peripheral actions of mephenesin, methocarbamol and diazepamBr. J. Pharmacol.34(3)579-590(1968) 4.Parr, J.S., and Khalifah, R.G.Inhibition of carbonic anhydrases I and II by N-unsubstituted carbamate estersJ. Biol. Chem.267(35)25044-25050(1992)