Drug (Medication) Allergy - Fast Facts

This document has been developed by ASCIA, the peak professional body of clinical immunology/allergy specialists in Australia and New Zealand. ASCIA information is based on published literature and expert review, is not influenced by commercial organisations and is not intended to replace medical advice.

For patient or carer support contact Allergy & Anaphylaxis Australia or Allergy New Zealand.

ASCIA PC FAST FACTS Drug Allergy 2023121.41 KB

An allergic reaction to a drug (medication) is called ‘immediate’ when it occurs within one to six hours after taking a medication. An allergic reaction to a drug is called ‘non-immediate’ when the reaction occurs after 24 hours of starting a medication.
Signs of mild to moderate allergic reactions to a drug can include itchy rashes (hives or welts), swelling (angioedema) of lips, face or eyes, tingling mouth, abdominal (stomach) pain and vomiting.
Sometimes rashes due to an infection are mistaken as an allergic reaction to a drug.
Severe non-immediate rashes due to drugs are associated with fever, flu-like and other systemic symptoms, and can be life-threatening. These are called severe cutaneous adverse reactions (SCAR) and require urgent specialist care.
Anaphylaxis is the most severe type of allergic reaction and should always be treated as a medical emergency. Anaphylaxis requires immediate treatment with adrenaline (epinephrine), injected into the outer mid-thigh. Delayed treatment can result in fatal anaphylaxis. Anaphylaxis to drugs can affect breathing, the heart and blood pressure. Anaphylaxis to drugs is more likely when a drug is given by an injection, than when it is taken orally.
When drug allergy is uncertain, skin testing or a medically supervised test called a ‘drug challenge’ can be conducted by clinical immunology/allergy specialists in hospital clinics.
If a true drug allergy is diagnosed after specialist assessment, the drug must be avoided. Documentation of a diagnosed drug allergy should be recorded in My Health Record, as well as in GP, hospital and pharmacy records. People with a diagnosed drug allergy should always carry or wear medical alert identification.
Aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) can cause reactions in some people. These include flushing, itchy rashes, blocked/runny nose and sometimes severe asthma, usually within an hour of taking a tablet. Aspirin allergy is more common in people with nasal polyps and asthma. Other people may have an intolerance to all NSAIDs. These reactions should be investigated by a clinical immunology/allergy specialist.
Allergic reactions to antiseptics, latex and anaesthetic drugs given during operations are rare but can be serious. Allergic reactions to chlorhexidine antiseptics are increasing in frequency and are possibly related to more common usage of chlorhexidine-containing products.
Allergic reactions can occur to complementary and alternative medicines, despite them often being considered natural and safe. Allergic reactions to herbal medicines are more common in people with other allergic conditions, such as asthma or allergic rhinitis (hay fever).