The safety of heartworm-preventative products in heartworm-positive cats has traditionally been evaluated with a study design where adult D. immitis are removed from infected dogs and surgically implanted into cats. An alternate study model was developed to establish adult infections in cats for subsequent product safety testing. Eighty adult cats were each inoculated with 60 D. immitis L3 on test day (TD) 1. The cats then were maintained for eight months to allow for the development of adult worms. Antigen/antibody testing, as well as echocardiographic imaging, were performed to confirm and estimate adult worm burdens. Thirty-five cats determined to have clinically relevant D. immitis infections were blocked by infection intensity score and randomised to one of four treatment groups: 1) 0x (nine cats); 2) 1x dose imidacloprid + moxidectin (nine cats); 3) 5x dose of imidacloprid +moxidectin (nine cats); and 4) selamectin 1x dose (eight cats). Treatments were topically administered on TD 250. Cats in groups 1, 2 and 4 received additional treatments on TD 278 and 306. On TD 288, group 3 cats were euthanised for recovery of adult heartworms. All other cats were euthanised on TD 334. No adverse events attributable to treatment with the test articles were observed during the study. The geometric mean numbers of adult D. immitis recovered from groups 1–4 were 2.73, 2.86, 3.24 and 3.97, respectively. There were no statistically significant differences in the adult D. immitis recovery between groups (p = 0.5356). The results of the study indicate that cats currently infected with D. immitis can be safely treated with 10% imidacloprid + 1% moxidectin, even at dosages five-fold higher than recommended for clinical use.
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Arther, R.G., Atkins, C., Ciszewski, D.K. et al. Design and Testing of a Natural Dirofilaria immitis Infection Model to Evaluate the Safety of an Imidacloprid plus Moxidectin Combination in Cats. Parasitol Res 101, 69–76 (2007). https://doi.org/10.1007/s00436-007-0613-9
- Adult Worm
- Adult Heart
- Label Dose