Revolution for cats works by delivering a drug called selamectin through the skin and into the bloodstream, where it spreads throughout your cat’s body to kill fleas, prevent heartworm, and eliminate several other parasites. You apply it as a liquid to one spot on the back of your cat’s neck, and from there it absorbs into the blood and concentrates in the skin’s oil glands, turning your cat’s own body into a hostile environment for parasites.
How Selamectin Kills Parasites
Selamectin belongs to a class of drugs that target a specific type of nerve channel found in insects and parasitic worms but not in mammals. These channels normally open and close to regulate nerve signals. Selamectin locks them permanently open, flooding the parasite’s nerve and muscle cells with chloride ions. This essentially short-circuits the nervous system, preventing the parasite from moving, feeding, or functioning. The result is paralysis and death.
This mechanism is why Revolution is safe for cats but lethal to parasites. Mammals don’t have these particular nerve channels, so the drug passes through your cat’s body without disrupting normal function.
How It Absorbs and Spreads
After you part the fur and apply the liquid to the skin at the base of your cat’s skull, selamectin absorbs through the skin and enters the bloodstream. Plasma levels peak about 15 hours after application. From there, the drug concentrates in the sebaceous glands (the tiny oil-producing glands attached to hair follicles across your cat’s entire body). This is key to how it works against external parasites like fleas and ear mites: the drug essentially coats your cat’s skin and fur from the inside out, so any parasite that bites or feeds on skin debris gets a lethal dose.
Because it also circulates in the blood, selamectin reaches internal parasites too. Heartworm larvae traveling through tissue, roundworms in the gut, and hookworms all encounter the drug systemically.
What Revolution Protects Against
Original Revolution covers five parasites in cats: fleas, heartworm, ear mites, roundworms, and hookworms. Each one is targeted slightly differently depending on where it lives in the body.
For fleas, the drug kills adults on your cat and also prevents flea eggs from hatching, which breaks the reproduction cycle in your home. In FDA testing, Revolution Plus (the newer formulation) reduced flea counts by 72.5% within 12 hours of application and 98.1% by 24 hours. By 48 hours, flea kill reached 100%.
For heartworm, selamectin kills the immature larvae that mosquitoes deposit on your cat’s skin. These larvae normally burrow into tissue and migrate toward the heart over several months, maturing as they go. Monthly doses of Revolution eliminate them during these early migrating stages, well before they can reach the heart and cause disease. The drug works in concert with your cat’s immune system to destroy these susceptible larval forms.
Ear mites, roundworms, and hookworms are all killed through direct exposure to selamectin circulating in the blood or concentrated in skin secretions.
Revolution vs. Revolution Plus
Revolution Plus adds a second active ingredient called sarolaner alongside selamectin. The practical difference is tick protection. Original Revolution does not kill ticks. Revolution Plus treats and controls blacklegged ticks, Gulf Coast ticks, and American dog ticks, while also providing stronger flea protection. If your cat goes outdoors or lives in an area where ticks are a concern, Revolution Plus covers that gap. Both versions protect against the same five core parasites (fleas, heartworm, ear mites, roundworms, hookworms).
Dosing by Weight
Revolution is approved for cats 8 weeks of age and older. The dose depends on your cat’s weight, and each weight range has a color-coded tube:
- Up to 5 lbs: Mauve cap, 15 mg
- 5.1 to 15 lbs: Blue cap, 45 mg
- 15.1 to 22 lbs: Taupe cap, 60 mg
Cats over 22 pounds need a combination of tubes to reach the correct dose. You apply it once monthly, always to the skin at the base of the skull where your cat can’t lick it off.
After You Apply It
Revolution is considered waterproof within 2 hours of application, but the manufacturer recommends waiting 24 hours before bathing your cat. Bathing shortly before application can also reduce effectiveness, since wet or recently washed skin may interfere with absorption. In practice, most cats rarely need baths, so this is mainly relevant if your cat gets into something messy around the time of treatment.
You don’t need to keep other pets or children away for long. Once the application site is dry to the touch (usually within a couple of hours), normal contact is fine.
Side Effects
Revolution has a strong safety record in cats. The most commonly reported reaction is temporary hair loss at the application site, sometimes with mild skin irritation. This occurred in about 1% of treated cats in clinical trials. The hair grows back on its own.
Less common reactions, seen in 0.5% or fewer of treated animals, include vomiting, diarrhea, decreased appetite, lethargy, drooling, and muscle tremors. Post-approval reports have also included itching, hives, skin redness, and uncoordinated movement, though these remain rare. If your cat licks the application site before it dries, drooling is the most likely reaction and typically passes quickly.