Can I make a suggestion that since you have the cats on Advantage, that you switch to Avantage Plus, it is new on the market in NZ, and it does the same as Revolution, I am considering changing my kitties depending on the cost, I feel at least it is the same Brand it might not have any side effects, worth a try., remember you still have to worm them with Drontal for threadworms I think it is, as neither Revolution or Advantage plus do that.