When given daily to heartworm-microfilaremic dogs for 4 weeks, tetracycline drugs, particularly doxycycline, have
been shown to be highly effective against third-stage (L3) and fourth-stage larvae (L4), at least moderately effective
against juvenile heartworms highly effective in blocking embryogenesis, and gradual elimination of circulating
microfilariae, presumably by killing their Wolbachia endosymbionts. These drugs also have been shown to kill adult worms of other filarial species, but months to years are often required for this stage to die in these species.