Are there circadian and circannual variations in acute toxicity of phenobarbital in mice?

The present work aims to document the possible influence of the time of the year on the circadian pattern of phenobarbital acute toxicity in mice by determination of phenobarbital acute toxicity at four different months of the year (i.e. October, January, April, and July). Our data indicate an important variation of phenobarbital acute toxicity throughout the year, with the maximum mortality occurring in January (i.e. minimum LD50) the minimum in July (i.e. maximum LD50). Thus, the season, not often taken into account, is an important determinant in toxicological studies.