Efficacy of the avermectins against filarial parasites: a short review.

The avermectins are macrocyclic lactones produced by Streptomyces avermitilis. One of them has been chemically modified and given the non-proprietary name ivermectin. The compounds have shown efficacy against various stages of filarial parasites. With respect to pre-adult stages in the mammalian host, activity has been observed against Dirofilaria immitis in ferrets and dogs, and Dipetalonema viteae and Litomosoides carinii in jirds (Meriones); but activity has not been observed against the developing stages of Brugia spp. in jirds or Onchocerca spp. in cattle. The compounds have not shown activity against adult filarial worms, except in the case of Setaria equina in horses and possibly Dipetalonema viteae in jirds. With respect to the first state larva (microfilaria) in the mammalian host, efficacy has been observed against Dirofilaria immitis in dogs, Brugia malayi in multimammate rats (Mastomys), Dipetalonema viteae and Litomosoides carinii in jirds and Onchocerca spp. in horses and cattle; but activity has not been observed against microfilariae of Brugia pahangi in jirds or cats. Efficacy against filarial parasites has been observed following oral or parenteral administration of drug, sometimes at extremely low dosage. For example, a single oral dosage of 0.05 mg/kg was highly active against the third and fourth larval stages and microfilariae of D. immitis in dogs.