Methocarbamol (AHR 85) is a centrally acting muscle relaxant whose mode of action has not been established. It is used as an adjunct in the symptomatic treatment of musculoskeletal conditions associated with painful muscle spasm.

Methocarbamol is metabolized via dealkylation and hydroxylation followed by conjugation to form both glucuronides and sulfates. [1]

Methocarbamol results in a median terminal half-life, mean transit time, mean absorption time, and apparent oral clearance of 2.89 hours, 2.67 hours, 0.410 hours, and 16.5 mL/min/kg in the horse. Methocarbamol is rapidly absorbed and extensively metabolized after oral administration to horses as indicated by a short absorption time and modest systemic bioavailability of 54.4% in the horse. [1] Methocarbamol is a centrally acting muscle relaxant available in both IV and oral forms in cats. [2] Methocarbamol (100 mg/kg) does not change the heart rate, cardiac output, mean pulmonary arterial blood pressure, systolic, diastolic and mean aortic blood pressure, respiratory rate and arterial blood gases, but mild to moderate depression is observed in five of eight horses administered i.v. Methocarbamol, and in all horses administered oral Methocarbamol. Plasma Methocarbamol concentration declines very rapidly during the initial or rapid disposition phase after i.v. administration; the terminal elimination half-life ranged from 59 minutes to 90 minutes in horse. Peak plasma Methocarbamol concentrations following oral administration occur within 15 to 45 minutes in horse. [3]