METHOCARBAMOL DEGRADATION IN AQUEOUS-SOLUTION

The kinetics of the hydrolysis of methocarbamol to the corresponding d iol guaifenesin in aqueous solution was studied. Methocarbamol was rat her stable in acidic media but easily hydrolyzed in alkaline solution. The formation of an unknown compound, proved to be an isomer of metho carbamol [the 3-(2-methoxyphenoxy)-propanediol 2-carbamate] is involve d. The amounts of methocarbamol and the two degradation products resul ting from storage of methocarbamol in various buffer solutions over a pH range of 8.0 to 10.0 at 70-80 degrees C (ionic strength, 0.5 M), we re followed as a function of time by a reversed-phase HPLC stability-i ndicating method to clarify the degradation pathway of methocarbamol i n alkaline solutions. Analysis of the concentration-time profiles reve als that base-catalyzed methocarbamol hydrolysis proceeded mainly thro ugh the formation of its isomer. The observed degradation rates follow ed approximately pseudo-first-order kinetics at constant pH and temper ature.