A chewable flea control tablet, Comfortis contains spinosad, a chemical that attacks fleas' nervous systems. If your pet has fleas, you can watch them fall off his body within 30 minutes of his ingesting the tablet. Any adult fleas on a cat or dog should die within four hours of Comfortis administration; protection lasts for a month. Most animals tolerate Comfortis very well, and the drug has relatively few side effects.
Canine Vomiting and Other Side Effects
Dogs receiving Comfortis might experience vomiting, usually within 48 hours of drug consumption. In a three-month study of 330 dogs cited on the Comfortis label, approximately 12 percent experienced vomiting the first month, with the percentage nearly in half by the third month. If your dog throws up within one hour of receiving Comfortis, give him another tablet. Other side effects include lethargy, itching, diarrhea, loss of coordination, drooling, appetite and weight loss and, rarely, seizures.
Don't Mix With Ivermectin
Do not give your dog Comfortis at the same time that he receives a wormer containing ivermectin, often found in heartworm preventives. Dogs given the two medications at the same time have experienced excess salivation, seizures, twitching and blindness.
Feline Side Effects
In cats, vomiting was the most common side effect. In a study of 139 cats cited on the Comfortis label, approximately 28 percent experienced vomiting during the three-month study, generally the day they ingested the pill. If your cat throws up the pill within one hour of consumption, give him another. Other possible side effects include appetite and weight loss, diarrhea and lethargy. The Comfortis label states that there are no known contraindications for felines, although cats receiving an invermectin heartworm preventive should not receive the medications at the same time.