MFA is a convulsant poison. It causes severe convulsions in poisoned victims. Death results from respiratory failure.
For a variety of animals, the toxicity of methyl fluoroacetate has been determined orally and through subcutaneous injection. The dosage ranges from 0.1 mg/kg in dogs to 10–12 mg/kg in monkeys indicating considerable variation. An order of decreasing susceptibility has been determined within these animals which is: dog, guinea-pig, cat, rabbit, goat, and then likely horse, rat, mouse, and monkey. For the rat and mouse, the toxicity by inhalation has been investigated more fully than for other animals. The LD for the rat and mouse are 450 mg/m and above 1,000 mg/m for 5 minutes, respectively. In dogs, guinea-pigs, cats, rabbits, goats, horses, rats, mice, and monkeys, the pharmacological effects of this substance have been investigated by mouth and by injection. Methyl fluoroacetate causes progressive depression of respiration and is a convulsant poison in most animals. When applied to the skin it is not toxic, yet through inhalation, injection and by mouth it is. For the rat, cat and the rhesus monkey, the effects of methyl fluoroacetate have been determined similar to those of nicotine, strychnine, leptazol, picrotoxin, and electrically induced convulsions. The convulsive pattern is considered to be similar to that of leptazol. Little besides signs of asphyxia is found post-mortem in these animals. Estimations have been made for blood sugar, hemoglobin, plasma proteins, non-protein nitrogen, and serum potassium, calcium, chloride, and inorganic phosphate in a small number of rabbits, dogs, and goats. Blood changes include a rise of 20 to 60% in hemoglobin, a rise of up to 90% in blood sugar, a rise of 70 to 130% in inorganic phosphate, and a less significant rise in serum potassium with a terminal rise in non-protein nitrogen and potassium. The whole central nervous system is affected by methyl fluoroacetate just like with leptazol, with the higher centers being more sensitive than the lower ones. Small doses of methyl fluoroacetate have little effect on blood pressure yet in large doses it has an action similar to nicotine. It further stimulates the rate and volume of respiration and then causes failure of the respiration, probably central in origin as seen through graphic records. The knee jerk reaction appears to be accentuated through methyl fluoroacetate until convulsions occur due to the irradiation of the stimuli being so facilitated. Nervous conduction is increased and the threshold stimulus lessened in the reflex arc of a spinal cat. Methyl fluoroacetate reduces the electric convulsive threshold about 10 times in rats. The difficulties of treatments are stressed as methyl fluoroacetate is both a powerful convulsant and a respiratory depressant, yet suggestions for treatment in man are made. Methyl fluoroacetate presents a serious hazard as a food and water contaminant in the case that it is used as a poison against rodents and other vermin, as it is not easily detected or destroyed and is equally toxic by mouth and by injection.