Allergic Reactions to Medications

Any drug can cause an allergic reaction.

Symptoms or signs of allergic drug reactions include:

  • An itchy rash or hives
  • An asthmatic attack
  • Loss of consciousness
  • Swelling of a body part such as the lips or tongue

Drug side effects, not allergic reactions, include:

  • Diarrhea
  • Racing heart
  • Dry mouth
  • Heartburn

Many drugs can cause adverse side effects, and certain medicines can trigger allergic reactions. 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, which causes the symptoms asscoiated with drug allergy.

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, dizziness, fainting, anxiety, confusion, rapid pulse, nausea, diarrhea, and abdominal problems.

What Are the Most Common Drug Allergies?

The drug most people are allergic to is penicillin. Other antibiotics similar to penicillin can also trigger allergies. 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?

Your allergist diagnoses drug allergies 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 it is up to your allergerist to dertime what testing is indicated.

How Are Drug Allergies Treated?

The primary goal when treating drug allergies is symptom relief. Symptoms such as rash, hives, and itching can often be controlled with antihistamines, and occasionally corticosteroids.

For coughing and lung congestion, drugs called bronchodilators may be prescribed to widen the airways. For more serious anaphylactic symptoms -- life-threatening allergic reactions including difficulty breathing or loss of consciousness -- epinephrine may be given. Occasionally, desensitization is used for drug allergy. This technique decreases your body's sensitivity to particular allergy-causing agents. Tiny amounts of penicillin are injected periodically in increasingly larger amounts until your immune system learns to tolerate the drug. If you are severely allergic to certain antibiotics, there are alternative antibiotics your doctor can prescribe.

How Can I Be Prepared With a Drug Allergy?

If you have a drug allergy, you should always inform your health care provider before undergoing any type of treatment, including dental care. It is also a good idea to wear a MedicAlert bracelet or pendant, or carry a card that identifies your drug allergy.