An allergy to penicillin causes the body to produce inflammation-causing histamine in response to the presence of penicillin. Treatment for allergies to penicillin can range from taking antihistamines and corticosteroids, to an epinephrine shot for life-threatening reactions. Another treatment option is desensitization. However, this is only used when no other antibiotic is available.
Taking antihistamines may relieve mild allergy symptoms such as itchy skin rashes. Antihistamines such as diphenhydramine, which work by blocking the release of histamine during an allergic reaction, are often available over the counter; however, they are known to cause drowsiness. Corticosteroids may be necessary to treat more severe allergy symptoms. Most corticosteroids, which will require a prescription from your doctor, treat allergy symptoms by preventing and treating the inflammation caused by an allergic reaction. Oral or injected corticosteroids may be necessary for more severe symptoms such as wheezing, and topical corticosteroids may be applied on the skin to relieve itchy rashes.
Those who are truly allergic to penicillin, but nevertheless require treatment with it or another closely related antibiotic, may need to undergo a process of desensitization to teach their bodies to tolerate penicillin for the duration of the treatment. Desensitization can be performed using oral or intravenous medications. It's a process by which an expert allergist gives you the medication in a controlled, gradual manner, starting with very small doses and incrementally increasing them. People treated through desensitization will learn to tolerate the drug long enough to complete their overall treatment. Desensitization is done under supervision in an outpatient clinic or in an intensive care unit. However, desensitization will not work on people with certain types of allergic reactions to penicillin or certain immunologic reactions to antibiotics. Furthermore, desensitization is temporary, and any tolerance to penicillin will vanish within a day after the last treatment with penicillin.