Pharmacokinetics and bioavailability of methocarbamol in rats.

In a pharmacokinetic study, 15, 30, 60, and 150 mg kg-1 intravenous and oral doses of methocarbamol were administered to rats. Differences observed in plasma clearance values, i.e. 0.0203, 0.0156, 0.0123, and 0.0085 1 kg-1 min-1 for 15, 30, 60, and 150 mg kg-1, respectively, suggested a dose-dependent pharmacokinetic behaviour of the drug. Elimination according to a biocompartmental open model and Michaelis-Menten kinetics fits the plasma level data. Estimated Km and Vmax values were 38.49 +/- 3.71 mg l-1 and 1.24 +/- 0.06 mg l-1 min-1, respectively. After oral administration of 15, 30, and 60 mg kg-1 the peak plasma levels were reached earlier. The tmax values were 6, 6, and 10 min, respectively. After 150 mg kg-1 oral doses, peak plasma levels were reached later (tmax = 150 min). Estimated bioavailability ranged between 77 and 112 per cent.