Try Zymox - it's the ONLY medication that cleared up my himalayan's reoccurring ear infections! It's also over the counter and CHEAP. I buy mine on Amazon for about $12!
My himalayan Lilli Ann (pictured) has unfortunately had chronic ear issues ever since I rescued here. I took her to the vet and they diagnosed here with an ear infection. The medication prescribed didn't work but luckily my mom suggested Zymox which works wonders on all of her cats and dogs...