Stability of phenobarbital sodium in liquid pharmaceutical preparations.

Shelf-lives of liquid pharmaceutical preparations (injectable and oral solution) containing phenobarbital sodium, commercially available in Brazil, were predicted by accelerated stability test using isothermal method (at 37 degrees C, 50 degrees C and 75 degrees C). Data obtained in high temperature studies using Arrhenius relation were applied to predict shelf-lives at room temperature. The shelf-lives were calculated by linear regression analysis. UV difference spectrophotometry was used for phenobarbital determination. Thin-layer chromatography was used for separation and identification of phenylethylacethylurea, the main degradation product of phenobarbital.