Sounds like you are on the right track with his treatment. The invermectin is bitter, so I would make sure to have a snack ready after putting it in his mouth.
Your case is exactly the same as Charlie's, misdiagnosis for allergies. He also had yeast in his paws when I adopted him, chewed his feet. Vet did a swab between his toes, and there was yeast. Special shampoo took away the itch.
Take care and soon his skin will look so much better. -Deborah |