Drug Allergies

An allergic reaction is a hypersensitivity reaction of the immune system caused by a drug. The body becomes sensitized by the first exposure to the medication and the immune system is triggered. Subsequent exposure to the drug causes the immune (antibody) response and the release of histamine into the blood stream which leads to allergic symptoms.

Most drug allergies develop within a few hours to days of drug exposure and cause minor skin rashes and hives, which are not serious. However, life-threatening acute allergic reactions involving the whole body (anaphylaxis) can occur and require immediate medical care. Symptoms of anaphylaxis usually occur within minutes of drug exposure and can include swollen mouth, trouble breathing, a pounding heart, fainting and chest tightness. Serum sickness is a delayed type of drug allergy involving fever and joint pain. It occurs a week or more after exposure to a medication or vaccine.

Common allergy-causing drugs include penicillin and related antibiotics, sulfa-type drugs, barbiturates, pain killers, anticonvulsants, some insulin preparations and local anesthetics. A derailed history of allergic-type reaction after use of a medication is often considered the most reliable means of detecting drug allergy. Skin testing may confirm allergy to penicillin-type medications but may be ineffective (or in some cases, dangerous) for other medications.

In people who have an established drug allergy, avoiding the medication is the best way to prevent an allergic reaction. Alert your doctor and pharmacist of your allergy and ask them about cross-reactive drugs (drugs in the same class that may produce symptoms the first time they are taken). In some cases, patients can be 'desensitized' to a drug. This type of treatment uses increasing doses of the drug to induce tolerance over time, usually a matter of hours.

If you suspect that you are experiencing a drug allergy, stop taking the medication and call your doctor. Symptoms may occur as soon as 15 minutes after taking the medication. If you are having trouble breathing, experiencing wheezing or swelling in your throat or mouth, feel faint or experience chest tightness, call 911 or have someone drive you to the nearest emergency room. If you experience hives or rash, apply cold compresses to the skin or take a cool bath or an oatmeal bath to relieve the itching. Talk to your doctor or pharmacist about the use of antihistamines or corticosteroids to provide symptom relief.

If you have experienced a severe allergic reaction in the past, consider wearing an identification bracelet (e.g., Medic Alert) or necklace that names the medication to which you are allergic. Your doctor may suggest you buy an anaphylaxis kit and will teach you and your family when and how to use it. It is important that the anaphylaxis kit be carried with you at all times.