Flea treatment for cats living with dogs

Living with dogs makes cat flea treatment a bit more complicated — and there's one safety issue that's genuinely serious. Permethrin, which is found in many dog flea products including some popular spot-ons, is toxic to cats. Even indirect exposure — your cat grooming a recently treated dog — can cause seizures and can be fatal. So before anything else: what products are your dogs currently on, and are they spot-ons or tablets? Also, how heavy is your Siamese, and are you dealing with an active infestation or looking to keep things under control going forward?

Seresto collars for the dogs are fine — they use imidacloprid and flumethrin, neither of which poses the same contact risk to cats as permethrin. That simplifies things. For your Siamese with an active infestation at 4.5kg, I'd go with Advantage 80 for cats. It's a spot-on containing imidacloprid, which is cat-safe, kills adult fleas within 24 hours, and is effective for up to four weeks. At 4.5kg your cat sits in the 4–8kg range so the 80mg pipette is the right strength. Have you treated the home yet — furniture, carpets, the places she sleeps?

It really is — this is where most treatments fall short. Up to 95% of a flea infestation lives in the environment as eggs, larvae and pupae rather than on the animal. If you only treat your cat, the fleas in the carpets and soft furnishings will just keep reinfesting her. Use a household flea spray that contains an IGR — an insect growth regulator — which stops eggs and larvae developing. Indorex Defence is a solid choice for this and one can covers a full house. Vacuum thoroughly first, spray everywhere your cat and dogs rest, and wash bedding at 60°C. Do that alongside the Advantage 80 and you'll break the cycle.

If the collars are relatively recent and still within their eight-month effective window, the dogs should be reasonably well covered. That said, during an active infestation it's worth checking with your vet whether a one-off adulticide treatment on the dogs would help clear things faster — not because the collars aren't working, but just to hit the infestation from all angles at once. The key priority right now is Advantage 80 on your cat and the household spray. That combination addresses the problem at its source.

Good plan. Apply the Advantage 80 to the back of your cat's neck where she can't groom it off, and keep her away from the dogs for a couple of hours while it absorbs — just as a precaution. With the household spray done at the same time, you should see a significant drop in flea activity within a few days. If it's persisting after four weeks, come back and we can look at whether a prescription product like Bravecto or Broadline might be worth considering.