Bravecto kills fleas and ticks on cats by attacking their nervous systems from the inside out. The active ingredient, fluralaner, absorbs through your cat’s skin into the bloodstream, where it circulates through body tissues and fluids. When a flea or tick feeds on your cat, it ingests fluralaner and dies, typically within hours. A single topical application protects against fleas for a full 12 weeks.
How Fluralaner Targets Parasites
Fluralaner belongs to a class of drugs called isoxazolines. It works by blocking a specific type of nerve receptor in fleas and ticks called the GABA receptor. In a healthy parasite, these receptors help regulate nerve signals by allowing chloride ions to flow through tiny channels, which keeps the nervous system calm and controlled. Fluralaner binds tightly to these channels and shuts them down.
Without functioning GABA receptors, the parasite’s nervous system goes into overdrive. Nerve signals fire uncontrollably, causing hyperexcitation, then paralysis, then death. What makes fluralaner particularly effective is how persistently it binds: once it locks onto an activated receptor, the connection doesn’t reverse even after repeated nerve impulses. The parasite has no way to recover.
This mechanism is highly selective for arthropods like fleas and ticks. Mammalian GABA receptors have a different structure, so fluralaner has very little affinity for your cat’s own nervous system at the doses used.
How the Drug Reaches Fleas and Ticks
Bravecto for cats comes as a topical solution applied to the skin between the shoulder blades. From there, fluralaner absorbs through the skin into the bloodstream and distributes throughout your cat’s body. The highest concentrations accumulate in fat tissue, followed by the liver, kidneys, and muscle. This wide distribution means the drug is present in the blood and tissue fluids that parasites consume when they bite.
The primary way fleas and ticks encounter fluralaner is through feeding, not through contact with the skin surface. A flea or tick needs to bite your cat and begin a blood meal to ingest a lethal dose. This means parasites aren’t repelled before they attach. They land, feed, and die. Fluralaner has an exceptionally long half-life in cats, around 130 days on average (ranging from 92 to 170 days), which is why a single dose provides weeks of continuous protection.
How Quickly It Kills
Bravecto kills 100% of fleas within 8 hours of initial treatment. That speed matters because female fleas can begin laying eggs within 24 hours of their first blood meal. By killing fleas before they have a chance to reproduce, Bravecto effectively breaks the flea life cycle in your home.
Studies show fluralaner reduces flea egg production by 99.9% within 48 hours of treatment. In one evaluation, the two eggs that were collected from a treated animal failed to develop into adult fleas. After that initial period, not a single egg was produced from any reinfestation over a 122-day study period. Every female flea died before it could lay eggs. This is a meaningful advantage over treatments that kill more slowly, since a surviving flea can deposit dozens of eggs into carpets and bedding each day.
What Parasites It Covers
Bravecto’s topical solution for cats is labeled to treat and prevent infestations from several specific parasites, with different durations of protection depending on the species:
- Cat fleas: 12 weeks of protection
- Black-legged ticks: 12 weeks of protection
- Asian longhorned ticks: 12 weeks of protection
- American dog ticks: 8 weeks of protection
The shorter coverage window for American dog ticks means you may need to reapply sooner if that species is common in your area. Your cat must be at least 6 months old and weigh at least 2.6 pounds to receive Bravecto.
There is also a formulation called Bravecto Plus, which adds a second active ingredient (moxidectin) to extend coverage to internal parasites including heartworm. Bravecto Plus is applied every 2 months rather than every 3.
Potential Side Effects
Most cats tolerate Bravecto without problems, but the isoxazoline drug class carries a known risk of neurologic side effects. The FDA has documented reports of muscle tremors, loss of coordination, and seizures in some cats and dogs treated with isoxazoline products. These reactions can occur even in animals with no prior history of seizures.
Mild and temporary side effects at the application site, such as hair loss or skin irritation, are also possible with the topical formulation. If your cat has a history of neurologic issues, that’s worth discussing with your vet before starting treatment, since the drug’s long half-life means it stays in the body for months after application.