Macrocyclic Lactones for Parasite Control in Equids

Abstract

Macrocyclic lactones (MLs) revolutionized parasite control in horses and other animals. They are unique in that they are effective against arthropods and nematodes. The first of the widely used avermectins was ivermectin. In 1983, it was marketed for use in horses as an injectable formulation but was withdrawn in 1984 after about a year and half on the market because of adverse problems. It was replaced by a paste formulation and an oral/stomach tube liquid formulation. Ivermectin is highly active on bots, ascarids, large and small strongyles, pinworms, strongyloides, stomach worms, and some other internal parasite species. Another ML, moxidectin, became available in 1997 as a gel formulation for oral administration. The parasiticidal activity of this compound is similar to ivermectin except efficacy is less on the common bot (Gastrophilus intestinalis) but high on encysted small strongyles. Recently however lower than initial activity on ascarids and small strongyles has been found for both ivermectin and moxidectin.

Comparative plasma and milk dispositions, faecal excretion and efficacy of per os ivermectin and pour‐on eprinomectin in horses

“…Ivermectin as a paste formulation is highly effective in removing gastrointestinal nematodes, including strongyles (Lyons & Tolliver, ). In the current study, the FECR values determined after paste administration were consistent with findings obtained in previous studies.…”

Epidemiological study on factors influencing the occurrence of helminth eggs in horses in Germany based on sent-in diagnostic samples

“…Moreover, macrocyclic lactones are able to eliminate tissue migrating larval stages of Parascaris spp. (Reinemeyer and Nielsen 2017 ; Lyons and Tolliver 2012 ; Lindgren et al 2008 ) and this property is expected to cause the better/longer lasting protection than pyrantel and fenbendazole, which are both only active against gut luminal stages of the parasite (Luksovsky et al 2013 ; Armstrong et al 2014 ; Lindgren et al 2008 ).…”

Equine cutaneous gasterophilosis in an era of selective parasite control

“…Thus, treating all horses in this period would be one option to prevent reinfection in the following season. Macrocyclic lactones control bot flies efficiently, with oral formulations of both ivermectin and moxidectin producing a reduction in larvae (Klei et al, 2001; Reinemeyer et al, 2000), although the first one is more efficient (Lyons et al, 1992; Lyons & Tolliver, 2012). However, most clinical trials to date have been carried out on endogenous larval stages of G. intestinalis and not other species.…”