Most times a drug allergy can be diagnosed based on your symptoms. Sometimes, though, drug allergies are harder to pin down. In these cases allergy testing may be required.
Skin test: First, a skin prick is applied to the skin. After ten minutes, if the skin prick is negative an intradermal is applies and read within ten to fifteen minutes. Skin tests only work for some types of drugs, like the antibiotic Penicillin.