Although it been quite a long time ago, I do seem to remember that my vet at that time would prescribe both interferon and antibiotics at the same time when my cats had URI's. He's the only vet that has ever done this and I don't know if it really helped or not. My cats were only it for about 2 weeks or so. He would also always prescribe antibiotics after teeth cleanings and my future vets never did.They'd only prescribe it if a tooth was pulled.