Efficacy of Simparica Trio® (sarolaner, moxidectin, and pyrantel chewable tablets) against circulating microfilariae in dogs infected with Dirofilaria immitis

Canine heartworm disease remains a global threat despite the availability of multiple preventive options, a challenge compounded by the emergence of macrocyclic lactone-resistant heartworm strains, especially in the USA. Circulating microfilariae play a pivotal role in heartworm transmission, serving as a continuous infection reservoir for mosquito vectors. Therefore, targeting this life cycle stage is critical in the framework of a comprehensive and multimodal heartworm prevention strategy. A randomised, blinded, negative-controlled laboratory study evaluated the efficacy of Simparica Trio® (Zoetis Inc., Parsippany, NJ, USA), containing a minimum dosage of 1.2 mg/kg sarolaner, 24 µg/kg moxidectin, and 5 mg/kg pyrantel, against circulating microfilariae. Dogs naturally infected with heartworm and harbouring circulating microfilariae were enrolled in the study. Twelve dogs received a single treatment with Simparica Trio as per recommended label dosage, and efficacy was compared with an untreated control group of 10 dogs weekly for 28 days. There were no adverse events recorded in this study. Following a single oral dose of Simparica Trio, a significant reduction in microfilaria counts in the Simparica Trio-treated group relative to the control group was first detected within 7 days ( P < 0.0001), resulting in an efficacy of 99.9% (98.9%) based on geometric (arithmetic) means. The efficacy remained at least 99.9% (≥ 99.5%) based on geometric (arithmetic) means for 28 days ( P < 0.0001). A single oral dose of Simparica Trio was highly effective against circulating microfilariae in naturally infected dogs with D . immitis for 1 month. Combining its effects on migrating L 4 stages and circulating microfilariae coupled with mosquito killing, Simparica Trio offers a multimodal, holistic, integrated solution to heartworm prevention in dogs.