She says she’s allergic to penicillin, but her doctor calls it a “drug hypersensitivity.” What’s the difference?

Q.My wife can’t take penicillin or any drug in the penicillin family. She says she’s allergic to penicillin, but her doctor calls it a “drug hypersensitivity.” What’s the difference?

A.An allergic reaction to a drug is one form of drug hypersensitivity. Both fall under the larger category of adverse drug reactions—unwanted effects of a particular medication. Most adverse drug reactions don’t involve the immune system, but both allergy and hypersensitivity do. They occur when a person’s immune system reacts to the medication or to substances produced when the body processes the medication.

An allergic reaction most frequently occurs when the drug is given either intravenously (into a vein) or by injection. It is less likely when a drug is taken by mouth. The allergic reaction occurs only when a person has had a previous exposure to the medication. Penicillin is among the  medications most likely to trigger an allergic reaction. Other antibiotics also cause problems for some people.

Symptoms of drug hypersensitivity include hives or a skin rash, wheezing, and  swelling. The most serious reaction is anaphylaxis, which is potentially life-threatening and thus a medical emergency. Although these symptoms generally occur within minutes to hours after taking the drug, they can also appear a week after the medication has been discontinued.

If symptoms are mild, the reaction usually goes away once the person stops taking the medication. If symptoms are severe or longer-lasting, a doctor may give  corticosteroids, antihistamines, or other drugs to reverse the reaction.

Most of the time, if a person is allergic to a particular medication, a doctor can find an effective alternative.