Allergies: Allergies to medications

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

What are the symptoms of a medicine allergy?

Symptoms can range from mild to life-threatening. Even in people who aren't allergic, many medicines 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, diarrhoea and abdominal problems.

Which medicines most often cause an allergic reaction?

The most common medicine associated with allergies is penicillin. Other antibiotics similar to penicillin can also trigger allergic reactions.

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

How are medicine allergies diagnosed?

A doctor diagnoses a medicine 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 medicines, and in some cases it could be dangerous. If you have had a severe, life-threatening reaction to a particular medicine, your doctor will simply rule out that medicine as a treatment option for you. Conducting an allergy test to determine if the initial reaction was a 'true' allergic response isn't worth the risk.

How are medicine allergies treated?

The primary goal when treating medicine 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 medicines called bronchodilators may be prescribed to widen the airways. For more serious anaphylactic symptoms - life-threatening reactions including difficulty breathing or loss of consciousness - adrenaline (or epinephrine) may be given.

Occasionally desensitisation is used for penicillin 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 medicine.

If you are severely allergic to certain antibiotics, there are alternative antibiotics your doctor can prescribe.

How can I be prepared?

If you have a medicine allergy, you should always inform a doctor before undergoing any type of treatment, as well as your dentist. It is also a good idea to wear a MedicAlert bracelet or pendant, or carry a card that identifies your medicine allergy. In cases of emergency it can save your life.