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Allergies Health Center

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Drug Allergies

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Many drugs can cause adverse side effects and certain medicines can trigger allergies. In an allergic reaction, the immune system mistakenly responds to a drug by creating an immune response against it. The immune system recognizes the drug as a foreign substance and the body produces certain chemicals, such as large amounts of histamine, in an attempt to expel the drug from the body.

What Are the Symptoms of a Drug Allergy?

Symptoms of a drug allergy can range from mild to life-threatening. Even in people who aren't allergic, many drugs can cause irritation, such as an upset stomach. But during an allergic reaction, the release of histamine can cause symptoms like hives, skin rash, itchy skin or eyes, congestion, and swelling in the mouth and throat.

A more severe reaction may include difficulty breathing, blueness of the skin, dizziness, fainting, anxiety, confusion, rapid pulse, nausea, diarrhea, and abdominal problems or the life threatening anaphylaxis.

What Are Some Common Drug Allergies?

The most common drug allergy is penicillin. Other antibiotics similar to penicillin can also trigger allergic reactions.

Other drugs commonly found to cause reactions include sulfa drugs, barbiturates, anticonvulsants, insulin, and iodine (found in many X-ray contrast dyes).

How Are Drug Allergies Diagnosed?

A doctor diagnoses a drug allergy by carefully reviewing your medical history and symptoms. If your doctor suspects that you are allergic to an antibiotic such as penicillin, he or she may do a skin test to confirm it. However, skin testing does not work for all drugs and, in some cases, it could be dangerous. If you have had a severe, life-threatening reaction to a particular drug, your doctor will simply rule out that drug as a treatment option. Conducting an allergy test to determine if the initial reaction was a "true" allergic response isn't worth the risk.


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