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Active Ingredients of Frontline Plus

| Updated September 26, 2017

The medication Frontline Plus is a flea and tick controlling product that will kill every stage of ticks and fleas, including the deer tick that is a carrier of debilitating Lyme disease. Frontline Plus will also kill flea eggs and flea larvae, thereby putting an effective end to the breeding cycle of fleas.Within about 18 hours after application, every flea on the dog or cat will be dead. For ticks, it takes a little longer, about two days. The medication must be applied to the back of the animal's neck by a special applicator. This is so the animal will not lick at the medication. After applying the Frontline Plus, you should wash your hands thoroughly and try not to touch the animal for a day; if you do, wash your hands after touching the animal. There are two main active ingredients in Frontline Plus.


Frontline Plus contains fipronil, which is a manufactured insecticide that works on a cellular level on adult fleas and ticks. It seeps into the cells and blocks chlorine molecules from passing into the cell. This stops the nervous system from working and paralyzes the insect. Because fipronil is so strong, it only needs to be applied once a month to continuously kill fleas and ticks. Once it is applied with an oily liquid to keep it on the skin of the dog or cat, it slowly seeps into the hair follicles and the oil glands of the animal where the fleas and ticks live.


The other active ingredient in Frontline Plus is methoprene. It is an insect growth regulator or IGR. This ingredient works by affecting the eggs and larvae of fleas, not the adults. An IGR acts like the flea's growth hormone, the substance that allows a flea to grow into an adult. Methoprene interrupts the normal levels of growth hormone, which makes the juvenile flea stop growing. It does not go through the molting stage, which makes it die. Frontline Plus contains methoprene to stop the juvenile cycle and fipronil to stop the adults.


Because fipronil and methoprene are strong, powerful insecticides, take precautions when using Frontline Plus. Always point the applicator away from your face, especially the eyes, and wash hands thoroughly after applying the medicine. Watch for any signs of allergic reaction in the cat or dog that has received a dose of Frontline Plus. Some animals are sensitive or allergic to the ingredients, and that means the active ingredients as well as the nonactive ingredients. If the animal shows signs of itching, restlessness, vomiting, lethargy or difficulty breathing, take it to the veterinarian immediately.