While some are effective, many, unfortunately, only protect a very small portion of the animal, generally around the neck area. Comeb your cat's fur frquently with a fine toothed comb to remove fleas and eggs. Robot Check Flea Treatment Cat Medicine Dog Cat Topical drops kill fleas by depositing chemicals into their nervous system. How do flea medications work . The active ingredients in flea and tick sprays work in the exact same way as flea and tick spot ons: However, they have similar results. Flea collars work by either emitting a pesticide into the area around your pet or releasing one that is absorbed by your pet's skin. A spot on treatment is usually applied on shoulder blades and the tip of the tail. Dunk the comb into hot soapy water after each pass throgh the fur to drown the fleas. Most topical medications last a month. It works by blocking nerve receptors in the insect, killing adult fleas on the animal in about 30 minutes. Fipronil spreads ov...