The effect of prior treatment with 4-dimethylaminophenol (DMAP) on animals experimentally poisoned with hydrogen cyanide

Six dogs were given sufficient oral 4-dimethylaminophenol (DMAP) to produce a peak methaemoglobin level of 12–15%. Five out of the six dogs then survived an intravenous injection of approximately 2 LD₅₀'s of hydrogen cyanide given when the methaemoglobin had reached 8–10%. The sixth dog died after 44 min. When the same dose of hydrogen cyanide was given to dogs, not previously given DMAP, all three died within 11/2 min. It was concluded that prior treatment with oral DMAP provided a large measure of protection against cyanide poisoning. Comparison of cyanide levels in whole blood and plasma in the two groups of dogs lent support to the hypothesis that methaemoglobin complexed with cyanide in the erythrocytes causing the plasma cyanide to remain lower than it did in unprotected animals.