Trifexis and Interceptor have different use cases, so they cannot be compared to each other. Trifexis is designed to target fleas along with heartworm. Interceptor, on the other hand, is designed to treat a wide variety of worms only. If your dog doesn't need treatment for fleas, then using Trifexis would be wasteful. Additionally, flea medication takes a toll on your dog's body. If your dog needs treatment for just worms and not fleas, you should stick to Interceptor.