Allergies to medications

Any medication has the potential to cause non-allergic side effects, but some people can also have allergic reactions to specific medication. All medication, including prescription medication or over-the-counter medication bought from supermarkets and pharmacies, can trigger allergies in some people, but some types are more likely to cause allergies than others.

Allergies are not the same as the non-allergic side effects that are listed in Consumer Medicine Information (CMI) sheets for prescription medication. The CMI includes detailed information about the medication in plain English, including use, side effects and precautions. Your pharmacist can give you the CMI for your medication.

You should also ask your pharmacist for advice if you buy over-the-counter medication. They can advise you about side effects and possible interactions with other medication you are taking.

Causes of allergies to medication

Any medication could cause an allergic reaction, but some are more likely to than others, including:

• aspirin and non-steroidal anti-inflammatory drugs (NSAIDs)
• antibiotics – penicillin and sulfonamide antibiotics
• chemotherapy drugs for treating cancer
• medication for autoimmune diseases such as rheumatoid arthritis
• corticosteroid creams or lotions
• medication for people with human immunodeficiency virus infection (HIV)

Of these types, the two that commonly cause allergic reactions are aspirin and similar pain-relieving medication, and sulfonamide antibiotics.

Severe allergic reaction (anaphylaxis) to medication

Severe allergic reaction, also known as anaphylaxis, after taking a medication is life threatening. Symptoms of a severe allergic reaction include:

• difficult or noisy breathing
• swelling of the tongue
• swelling or tightness of the throat
• difficulty talking or a hoarse voice
• wheezing or coughing
• persistent dizziness or collapse
• paleness and floppiness in young children

Milder allergic symptoms that can occur before a severe allergic reaction include:

• swelling of the lips, face, eyes
• hives or welts
• tingling mouth
• abdominal pain and vomiting

If you have experienced any of these symptoms after taking a medication, you are at greater risk of having another severe reaction when you take the same medication. Most people with these allergies are allergic to only one medication, but some people are allergic to more than one. You should ask your doctor to refer you to a medical specialist (allergist/clinical immunologist).

If you are at risk of a severe allergic reaction, you should:

• have a severe allergic reaction action plan
• carry an adrenaline autoinjector (EpiPen® or AnaPen®) to treat a severe allergic reaction
• wear medical identification jewellery – this increases the likelihood that adrenaline will be administered in an emergency
• avoid medication (where possible) that may increase the severity of allergic reaction or complicate its treatment – such as beta blockers
• seek urgent medical assistance

Emergency treatment for severe allergic reactions

Emergency responses for a severe allergic reaction are:

• administer adrenaline with an autoinjector (EpiPen® or AnaPen®)
• always dial triple zero (000) to call an ambulance

Allergies to aspirin and other pain-relieving medication

Aspirin belongs to a group of medications called NSAIDs that help to reduce fever, pain and inflammation.

Side effects of high doses of aspirin that are not caused by allergies include bruising and stomach upset, but even higher doses can cause confusion and ringing in the ears. Allergic symptoms are different to these side effects and range from milder symptoms to anaphylaxis.

If you already have allergic conditions such as hives, hay fever symptoms or asthma, you are more likely to develop an allergy to aspirin or other NSAIDs than people who do not have these symptoms.

Allergies to sulfonamide antibiotics

Sulfonamide antibiotics can cause allergic reactions, ranging from mild or severe rashes to anaphylaxis. Several sulfonamide antibiotics are available with a prescription in Australia, either alone or in combination with another type of antibiotic. If you have an allergic reaction after taking a combination antibiotic, you should visit your doctor to talk about which antibiotic is causing your allergy.

Allergic reactions to sulfonamide antibiotics do not make it more likely that you will be allergic to sulfur powder, sulfite preservatives, or non-antibiotic sulfonamide medication, such as pain-relievers or water tablets (diuretics).

Symptoms of generalised allergies to medication

Once you have taken a medication and it is circulating in your blood, you can have a generalised allergic reaction within hours. Symptoms include:

• skin rash or hives
• itchy skin
• fever
• swelling
• runny nose
• itchy, watery eyes
• shortness of breath
• wheezing

Some allergic reactions to medication can occur days or weeks after you begin taking them and even continue after you have stopped taking them. These symptoms may include:

• serum sickness – fever, joint pain, rash, swelling and nausea
• anemia caused by medication – tiredness, shortness of breath and irregular heartbeat
• rash – swelling, swollen lymph nodes or the return of a previous hepatitis infection
• inflammation of the kidneys (nephritis) – fever, blood in the urine, swelling, confusion

Diagnosis of allergies to medication

If you think you may have an allergy to a medication, keeping a record (diary) of your symptoms can help you and your doctor to understand what is causing your symptoms.

In your diary, also include whether your symptoms occur:

• for a short time or longer – how long the symptoms lasted
• at night, during the day or when you wake up
• after you have taken a particular medication, either prescription or over the counter from a pharmacy or supermarket
• after you have taken a herbal medicine

If you have allergic symptoms after taking medication, you should visit your family doctor who will ask some questions about your symptoms. Your diary will help you to answer these questions accurately. To diagnose your allergy, your doctor will refer you to a specialist doctor known as an allergist or clinical immunologist.

Allergists can test for allergies using a number of methods, depending on the type of potential allergy. The allergist can test for allergies to some medication using a skin prick test or a blood test.

Testing and treating allergies and hypersensitivities to medication can be difficult and allergists can also use:

• graded challenge – four to five progressively larger doses of the medication are given up to the desired dose and any symptoms are recorded
• desensitisation treatment – begins with a very small dose and then the dose progressively increases over hours to days, with the aim of ‘switching off’ the allergic reaction to the medication

A number of methods claim to test for allergies but have not been medically or scientifically proven. They can be costly and could lead to dangerous avoidance of certain foods. The organisation representing allergists (Australasian Society of Clinical Immunology and Allergy) recommends that you do not use certain methods to have potential allergies tested, including:

• cytotoxic food testing
• electrodermal testing
• hair analysis
• iridology
• kinesiology
• pulse testing
• reflexology
• Vega testing

Always speak with your doctor if you are thinking of using a complementary medicine or therapy to test for allergies.

Diagnosis of aspirin allergy

Skin or blood allergy tests are not available to test for aspirin allergies. If your doctor needs to know whether you have sensitivity to aspirin (or an NSAID), you may have a graded challenge test under strict medical supervision.

Diagnosis of an allergy to sulfonamide antibiotics

Skin allergy tests are available for sulfonamide antibiotic allergies and can be used when you have had an allergic reaction to combination antibiotics. Once doctors know which antibiotic is causing your allergy, they can recommend the one you should avoid and which antibiotics you can take.

Treatment for allergies to medications

One strategy for allergies to medication is to manage the problem by avoiding that medication. In some situations, this can be difficult, especially if you have a chronic condition such as arthritis that needs ongoing treatment.

Other approaches that can be used include:

• antihistamine medication – for milder allergic reactions
• steroid tablets or injections – for more serious reactions
• desensitisation – for some medication allergies

Where to get help

• Your doctor
• In an emergency, always call triple zero (000)
• Emergency department of your nearest hospital
• NURSE-ON-CALL Tel. 1300 60 60 24 – for expert health information and advice (24 hours, 7 days)
• Medicines Line (Australia) Tel. 1300 MEDICINE (1300 633 424) – for information on prescription, over-the-counter and complementary medicines
• St John Ambulance Australia (Victoria) Tel. 1300 360 455
• Allergy and Anaphylaxis Australia Tel. 1300 728 000