My Husband Recently Took A Z-pac And Is Now Suffering

My husband recently took a z-pac and is now suffering from a severe rash which is spreading. His dr and the pharmacist recommended that he take benedryl. He has been taking it for two days now and the rash is not getting better. The affected areas are also swelling. We are also applying cortisone cream and he gets a little relief but it comes back worse. He also has Leukemia and I am getting worried that this has lasted so long. Should I contact the drug company or what. Please help.