Efficacy of the avermectins against filarial parasites: A short review

The avermectins are macrocyclic lactones produced byStreptomyces avermitilis. One of them has been chemically modified and given the non-proprietary name invermectin. 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 againstDirofilaria immitis in ferrets and dogs, andDipetalonema viteae andLitomosoides carinii in jirds (Meriones); but activity has not been observed against the developing stages ofBrugia spp. in jirds orOnchocerca spp. in cattle. The compounds have not shown activity against adult filarial worms, except in the case ofSetaria equina in horses and possiblyDipetalonema viteae in jirds. With respect to the first stage larva (microfilaria) in the mammalian host, efficacy has been observed againstDirofilaria immitis in dogs,Brugia malayi in multimammate rats (Mastomys),Dipetalonema viteae andLitomosoides carinii in jirds andOnchocerca spp. in horses and cattle; but activity has not been observed against microfilariae ofBrugia 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 ofD. immitis in dogs.