Allergies to medications

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

Allergies are not the same as the non-allergic side effects listed in the consumer medicine information that comes with many medications. This information describes the medication in plain language, including its use, side effects, and precautions. Your pharmacist can give you this information and can also advise you about over-the-counter medication, including possible side effects and interactions with other medication you are taking.

Which medications commonly cause allergies#

Any medication could cause an allergic reaction, but some are more likely to than others. The two that most commonly cause allergic reactions are aspirin and similar pain-relieving medication (NSAIDs), and sulfonamide antibiotics. Other antibiotics, such as penicillin, can also cause allergic reactions.

Severe allergic reactions (anaphylaxis)#

A severe allergic reaction, known as anaphylaxis, is life threatening. Milder allergic symptoms can sometimes occur before a severe reaction, and may include:

• swelling of the lips or eyes
• hives or welts
• a tingling mouth
• abdominal pain
• floppiness (in young children)

If you have experienced any of these symptoms after taking a medication, you are at greater risk of a severe reaction the next time you take it. Most people with these allergies are allergic to only one medication, but some are allergic to more than one. Ask your doctor to refer you to a specialist (an allergist or clinical immunologist).

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

• wear medical identification jewelry, which increases the likelihood that adrenaline will be given in an emergency
• avoid medication, where possible, that may increase the severity of an allergic reaction or complicate its treatment, such as beta blockers

If someone has a severe allergic reaction:

• always call your local emergency number (for example 911 in the US and Canada, 112 across the EU and many countries, 999 in the UK, or 000 in Australia)
• go to the emergency department of your nearest hospital

Aspirin and other NSAIDs#

Aspirin belongs to a group of medications called NSAIDs (non-steroidal anti-inflammatory drugs) that help reduce fever, pain, and inflammation. Side effects of high doses of aspirin that are not caused by allergies include bruising and stomach upset, and even higher doses can cause confusion and ringing in the ears. Allergic symptoms are different from these side effects and range from milder symptoms to anaphylaxis.

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

Sulfonamide antibiotics#

Sulfonamide antibiotics can cause allergic reactions, ranging from mild or severe rashes to anaphylaxis. They are available on prescription, either alone or combined with another type of antibiotic. If you have an allergic reaction after taking a combination antibiotic, see your doctor to work out which antibiotic is causing the allergy.

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

Other allergic reactions#

Once a medication is circulating in your blood, you can have a generalized allergic reaction within hours. Symptoms may include:

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

Some reactions can occur days or weeks after you begin taking a medication, and may even continue after you have stopped. These can include:

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

Keeping a record#

If you think you may have an allergy to a medication, keeping a diary of your symptoms can help you and your doctor understand what is causing them. In your diary, note:

• whether symptoms occur after taking a particular medication, whether prescription or over the counter
• how long the symptoms last, and whether they occur at night

If you have allergic symptoms after taking medication, see your doctor, who will ask questions about your symptoms. Your diary will help you answer accurately.

Diagnosis#

To diagnose your allergy, your doctor may refer you to an allergist or clinical immunologist. Allergists can test for allergies in a number of ways, depending on the type of suspected allergy, including a skin prick test or a blood test. Testing and treating medication allergies can be difficult, and allergists may 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
• desensitization – starting with a very small dose and gradually increasing it over hours to days, aiming to “switch off” the allergic reaction

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. Professional bodies representing allergists recommend against using unproven methods, so always speak with your doctor before using a complementary medicine or therapy to test for allergies.

Skin or blood allergy tests are not available for aspirin allergies. If your doctor needs to know whether you are sensitive to aspirin or another NSAID, you may have a graded challenge test under strict medical supervision. Skin allergy tests are available for sulfonamide antibiotic allergies and can be used when you have had a reaction to combination antibiotics. Once doctors know which antibiotic is causing the allergy, they can tell you which to avoid and which you can take.

Managing medication allergies#

One approach is to manage the problem by avoiding the medication that causes it. In some situations this can be difficult, especially if you have a chronic condition such as arthritis that needs ongoing treatment. In those cases, your doctor can discuss other approaches, such as a graded challenge or desensitization, with you.