Medication allergies can be difficult to diagnose. Some allergic reactions to drugs — particularly rashes, hives and asthma — can resemble certain diseases. An allergy to penicillin-type drugs is the only one that definitively can be diagnosed through a skin test. If there is no suitable alternative to the medication that you are allergic to, you may consider the need to undergo a drug challenge or desensitization.
If your allergist thinks you are at a low risk for a reaction, they may choose to perform a drug challenge. This involves taking approximately two to three step-up doses of the medication to determine tolerance.
Drug desensitization involves taking the drug in increasing amounts until you can tolerate the needed dose with minimal side effects. Desensitization only can help if you are taking the drug every day. Once you stop it — for example, when a chemotherapy cycle ends — you will need to go through desensitization a second time if you need the drug again.
If you have a medication allergy: