Comparative lethality of methanol, ethanol and mixtures in female rats

The lethalities of pure methanol and pure ethanol were compared to two mixtures of ethanol/methanol with the following percentages (95/5% and 65/35% v/v). This study was conducted to simulate situations of human exposure to denaturated alcohol (by 5% methanol) or adulterated alcohol (by 35% methanol). Four groups of female adult virgin albino rats were treated with the four mixtures. A fifth group was used as a vehicle control. Graded oral doses were given to eight animals per dose. Lethality over 24 h was used as an endpoint. The LD₅₀ was calculated for each of the four treatments on a molar basis. A dose‐response function for each mixture was plotted of percentage lethality vs. mmol kg⁻¹ equivalent to the given ml kg⁻¹ dose. Results showed a significantly different LD₅₀ estimates (P < 0.03) for the four mixtures. The order of lethal toxicity was as follows: 95/5% methanol/ethanol, pure methanol, pure ethanol then 65/35% methanol/ethanol. Slope comparisons indicated two pairs: 65/35% ethanol/methanol and pure ethanol yielding a steep slope, and 95/5% ethanol/methanol and pure methanol yielding a shallow slope. These data indicated that the acute lethality of ethanol/methanol mixtures is a complex unpredictable function. This toxicity presumably depends in a complicated way on the differences in the effective molecular weights of the two alcohols in each of the mixtures.