Toxicity of Haloxon

Abstract

Haloxon is a novel organophosphorus compound with a wide spectrum of anthelmintic activity in sheep and other domesticated animals. Data are presented which confirm that Haloxon has a low acute oral toxicity in many species of laboratory and domesticated animals and that it has a wide therapeutic index in sheep, the factor being 3–4 in the most susceptible animals, i.e. aged ewes, and about 5–7 in young lambs. Haloxon has been given to sheep subjected to a variety of environmental and stress factors such as concentrate feeding, pregnancy, copper deficiency, route of administration, and to sheep that had been treated with hexachlorophene, carbon tetrachloride or dioxathion; none of these factors appeared to increase the toxic hazards of the compound. Haloxon differs from many other organophosphorus compounds in that even at 10 times the anthelmintic dose in sheep there was only a slight to moderate depression in red cell cholinesterase activity. At high dose rates a neurotoxic response in the form of hindleg ataxia has been observed in a proportion of sheep and poultry after dosing, though no adverse side effects have been observed in the most susceptible types of sheep dosed with 3–4 times the anthelmintic dose. This is the first time a neurotoxic response of this type has been recorded in sheep.