Critical tests and safety studies on trichlorfon as an antiparasitic agent in the horse.

The research is focused on testing the efficacy and safety of single doses of trichlorfon, an antiparasitic agent, on horses, against varied parasitic infestations. It suggests that feeding this medicine to horses yielded better results and less toxicity than administering it through the stomach tube.

Efficacy Tests on different parasites

• Three different series of tests were carried out on a sample set of 46 horses. These tests aimed to assess the effectiveness of trichlorfon against different types of parasites, namely, bots, ascarids, pinworms, and large strongyles.
• In most cases, trichlorfon was mixed with the horse’s daily grain ration at a dose rate of 40 mg/kg of body weight. This method turned out to be more efficacious and less toxic than administering the drug through a stomach tube.
• In the cases of Gastrophilus intestinalis and Gasterophilus nasalis, the method achieved up to 100% parasite removal in the tests.
• The drug also demonstrated high removal rates of Parascaris equorum, irrespective of whether it was administered through intubation or the grain feeding methods, with the removal rates reaching up to 100%.
• The removal rates for Oxyuris equi were variable, ranging from as low as 11% to as high as 100%.
• Large strongyles, such as Strongylus vulgaris and Strongylus edentatus, however, were almost entirely resistant to the trichlorfon dosage of 40 mg/kg.

Safety Studies

• The study also included safety tests of trichlorfon on horses. Doses of 40 mg/kg and lower were typically well-received by the test horses.
• Higher dosage rates, such as 60 and 80 mg/kg, administered through the stomach tube led to conditions like severe colic and diarrhea.
• However, when the 80 mg/kg dose was mixed with the feed, it only caused a transient softening of the feces, suggesting it was better tolerated.
• Even when given at the high rate of 80 mg/kg in five consecutive doses (one week apart) to four horses, the drug was well-absorbed.
• In the large-scale clinical trials involving 2,294 treatments of trichlorfon at a dose rate of 35 to 40 mg/kg in various horses (pregnant and non-pregnant mares, stallions, suckling and weanling foals, yearlings, and horses in training), no significant adverse effects were noted. This further confirmed the relative safety of administering this drug in a feed at the investigated dose rates.