The Flea & Tick Drops flea treatment is suitable for large dogs (over 15kg) & will provide protection from fleas & ticks for up to 4 or 12 weeks (depending on pack size). The Flea & Tick Drops kill fleas instantly on contact & is very easy to use. Simply apply the drops to the back of your dog's neck at the base of the fur. Protecting your dog from fleas & ticks can help to reduce risk of skin irritation & infection.