Frontline Spot On Flea Drops Large Dog 20-40kg 3 Pipettes Frontline is an external flea treatment that works with immediate effect. Its formulated in such a way that means it does not need to enter your dogs blood system. This means it is suitable for pregnant/mother dogs without affecting her, or her puppies. * Work on contact via the dogs blood * Kills 98-100% of fleas & ticks * Works within 24 hours & protects for up to four weeks