These reactions usually get better with each dose, and go away completely when the ATG is stopped. After several days of receiving ATG your immune system will have had time to produce new antibodies against it. Serum sickness usually begins about a week after the first dose of ATG, and can continue for several weeks. It can cause a rash, joint pains and muscle aches, and make you feel like you have a bad flu. We give steroids to patients receiving ATG to decrease the chances and the severity of serum sickness.
Steroids reduce antibody production by the immune system.
There is no reason that someone cannot receive ATG more than once. Sometimes a person who did not respond to a first course will respond if ATG is given again, alone or with another immunosuppressive drug, such as cyclosporin. Additional courses of ATG can also be used to treat patients who relapse, especially if they responded to their first course. People who have received ATG before may have antibodies to the horse proteins. If ATG is given alone it works about half the time.