How do you treat a dog with a cold?

The best answer is the same way you would "treat" yourself if you had a simple cold - rest and drink plenty of fluids. The common cold is caused by a virus, so antibiotics are not effective and may actually make the dog sicker. You may choose to simply observe your dog at home to make sure he's not getting too sick, as most healthy dogs can work through a cold within 3-5 days. However, if your dog has a chronic health condition (such as diabetes, Cushing's, etc.), is on daily medications (prescribed by the vet, including prednisone and Rimadyl for arthritis), appears to be getting very ill or doesn't get better within a few days, you should take him to your vet.