Absorption
Methocarbamol is rapidly and completely absorbed after oral administration.
Distribution
The substance is detectable in the blood already 10 minutes after ingestion and after 30 - 60 minutes, the maximum level is reached in the blood. The plasma half-life of methocarbamol is approximately 2 hours.
Biotransformation and elimination
Methocarbamol and its two major metabolites are bound to glucuronic and sulfuric acids and are excreted almost exclusively by the kidneys. Approximately half of the applied dose is excreted in the urine within 4 hours, of which only a small portion is excreted as unchanged methocarbamol.
Renal Impairment
In patients with impaired renal function undergoing long-term hemodialysis treatment, clearance of methocarbamol was reduced by approximately 40% compared with a population with normal renal function, although the mean elimination half-life was similar in these two groups (1.2 and 1.1 hours, respectively).
Hepatic impairment
In patients with alcohol-related cirrhosis, the mean total clearance of methocarbamol was decreased by approximately 70% (11.9 l/h), and the mean elimination half-life was prolonged to approximately 3.4 hours, compared with a population with normal liver function. The fraction of methocarbamol bound to plasma proteins was reduced to approximately 40 to 45%, compared with 46 to 50% in an age- and weight-controlled population with normal liver function.