Drug allergies can be hard to diagnose. An allergy to penicillin-type drugs is the only one that can be definitively diagnosed through a skin test. Some allergic reactions to drugs – particularly rashes, hives and asthma – can resemble certain diseases.
Your allergist will want to know the answers to these questions:
- What drug do you suspect caused your reaction?
- When did you start taking it, and have you stopped taking it?
- How long after you took the drug did you notice symptoms, and what did you experience?
- How long did your symptoms last, and what did you do to relieve them?
- What other medications, both prescription and over-the-counter, do you take?
- Do you consume herbal medications or take vitamin or mineral supplements? If so, which ones?
Your allergist will also want to know whether you have had a reaction to any other drug. If you can, bring the suspected drug with you. This will help the allergist recommend alternatives as needed.
During a physical examination, your allergist will look for problems that are part of the drug reaction, along with nonallergic reasons for the reaction.
Depending on the drug suspected of causing the reaction, your allergist may suggest a skin test or, in limited instances, a blood test. A blood test may be helpful in diagnosing a severe delayed reaction, particularly if your physician is concerned that multiple organ systems may be involved. This rare reaction is known as “drug rash with eosinophilia and systemic symptoms” or, more commonly called “DRESS” syndrome.
If a drug allergy is suspected, your allergist may also recommend an oral drug challenge, in which you will be supervised by medical staff as you take the drug suspected of triggering a reaction (If your reaction was severe, a drug challenge may be considered too dangerous).