Effect of ethanol, glycerol, and propylene glycol on the stability of phenobarbital sodium.

The effects of ethanol, glycerol, propylene glycol, phosphate buffer, and ionic strength on the stability of phenobarbital sodium have been studied. Ethanol had the maximum stabilization effect followed by propylene glycol and glycerol when compared with the stability in water. The estimated half-lives at 50 degrees C (pH approximately 8) were 78, 95, 109, and 127 d in water and 20% aqueous solutions of glycerol, propylene glycol, and ethanol, respectively. The effects of phosphate buffer and ionic strength were negligible.