As far as I know, a cold is a virus and antibiotics will do no good. If the cat gets a sinus infections from the cold, that's another story. I bet the winter months (heating) dry out the cat's sinuses just like it does for humans. I would never give a cat any medication without first finding out if they need it. I did have a cat that came down with colds quite often and all I could do was treat the symptoms - such as eye drops or nose drops.... and then antibiotics if it impacted on her so badly that she got a sinus infection. She also had ear problems - spent lots of time and money at the Vets. Hope this helps!