Drug Allergy

A drug allergy is an immune-system reaction to a medication. This is different from an ordinary side effect (such as nausea or headache), which is not defined as an allergy. Drug allergies can range from mild (rash or hives) to severe (swelling or anaphylaxis). Immediate reactions usually occur within an hour of dose and cause hives, swelling, wheezing, or anaphylaxis. Delayed reactions can occur hours, days, or even weeks after initial dose. Many reported drug allergies (especially Penicillin allergy) are not true allergies, and allergists can sometimes confirm or rule out with skin testing or supervised drug challenge.