He needs to do more than just trade. Both the manager of the pharmacy and the manager of the store need to be notified of the mix up so they can do an audit of their procedures and fix the problem. The pharmacy will probably also have to list it in their regular reports to whatever agency they have overseeing them.
Something similar happened to my brother a couple years ago and he had such a severe reaction to the medication that he had to go to the ER. It nearly killed him. He didn't get another person's prescription, his prescription was filled with the incorrect medicine.