Do I have a valid lawsuit?

My grandfather was prescribed an antibiotic that gave him a reaction of shortness of breath and tightness in his chest. We took him to the emergency room and the doctor stated that the pains were from a fall two weeks prior. He had just left the hospital from a 5 day stay and was prescribed the medicine that stated if he had the reactions to take him to the emergency immediately. They never changed his medicine and sent him home. Today he was gasping for breath by simply trying to go to the rest room. He collapsed, we called 911, it took them over 20 minutes to arrive to our home and he died.