Antifilarial activities of benzazole derivatives. 3. Effects of benzothiazoles on third stage larvae and preadult worms of Acanthocheilonema viteae, Brugia malayi and B. pahangi in Mastomys natalensis.

Ten structurally defined benzothiazoles (5-methyl and the analogous 5-methoxy derivatives) with known macrofilaricidal and microfilaricidal activities were tested for efficacy against third stage larvae and preadult worms in Acanthocheilonema viteae, Brugia malayi, and B. pahangi infected Mastomys natalensis. Drugs were administered in single oral doses of maximally 100 mg/kg. The benzothiazoles were active against the two stages of the three species. Generally the 5-methoxy derivatives displayed slightly higher activity than the 5-methyl compounds. 6-Isothiocyanates (CGP 21306, CGP 20308) and 6-dithiocarbamic-S-(2-carboxyethyl)esters (CGP 21835, CGP 20376) were more active than thiocarbonylamides (CGP 21833, CGP 20309, CGP 26702, CGP 24589). 6-Dithiocarbamic-S-(sulfomethylsodium)esters (CGP 26701, CGP 24588) showed intermediate efficacy. A. viteae was usually slightly more resistant than the Brugia spp. Minimum curative doses (greater than 95% reduction of worms) against the two stages of the various species were either identical or preadult worms were slightly more resistant than third stage larvae. When these curative doses were compared with curative adulticidal doses or effective doses against microfilariae the various doses were very similar and never differed from each other by more than the factor 2.