Frontline uses fipronil as a classic external parasite treatment, covering fleas, ticks and lice, with a sebaceous reservoir that sustains roughly a month of activity. Broadline is a four-ingredient combination spot-on covering fleas, ticks, tapeworms and nematodes in one application.

Indoor cats whose risk is mainly fleas do fine with an external-only option. Cats that go outside, eat raw food or have recurring fleas more often need a combination covering internal parasites, and a broader spectrum makes weight band and minimum age checks more important.

A full-spectrum drop reduces the number of applications but increases ingredient exposure and the chance of local reactions. Frontline does not treat internal parasites, so tapeworm risk still needs handling. Neither replaces cleaning, since flea eggs and larvae remain in bedding and carpets.

Assess outdoor access and raw feeding, then let a vet decide whether a combined product is needed. Choose by weight, follow the label interval and do not stack products with the same actives. Drooling, tremors or lasting lethargy after application need immediate veterinary attention.