HI, my son has been on vancomycin and tobramycin for an eye infection along with cosopt. About a week in, he developed a sore throat with a white spot that developed into what looks like a large cold sore on the throat. He tested negative for strep and was told it was viral. Someone mentioned that the eye drops can sometimes drip down to the throat and and cause an irritation. Just wondering is this indeed might be aside effect of the drops.