I have the information with me from a pack of Advocate, and there is no mention of a severe skin reaction as in your photo, under the section on adverse reactions
if your vet is sure the condition of your cat is the result of using Advocate, then he or she should be in immediate touch with the makers, Bayer, about it, and getting second opinions too
someone should be paying for expert opinions and treatment for your poor cat, and that should not be you