How Long Does Capstar Work on a Dog?

If you want fast-acting flea relief for your dog, a Capstar tablet is the way to go. Within half an hour of administration, you'll literally see fleas dropping off your pet. Capstar's flea-killing ability doesn't last a long time, however. Its effectiveness only lasts between 24 and 48 hours, although it's safe to give your dog another tablet after that period. Available over the counter, Capstar isn't designed for long-term flea relief.

Nitenpyram, the active ingredient in Capstar, works by paralyzing and killing fleas, but not harming the dog. Because it's a relatively safe drug, Capstar can treat puppies over the age of 4 weeks, as long as they weigh at least 2 pounds. After treatment, give your dog a monthly topical or oral flea medication, as recommended by your veterinarian. While you could administer Capstar on a daily basis, that is far costlier than a monthly product, and Capstar does not kill flea eggs or ticks.