Understanding and identifying penicillin allergy and alternative medications for treatment.

Antibiotics have made an incredible difference to health care. Penicillins are the most prescribed class of antibiotics and are used to treat many common infections such as chest, sinus and urinary tract infections. Commonly prescribed penicillins include Amoxil and Augmentin.

For some people, taking penicillins can cause problems. Up to 20 per cent of Australians admitted to hospital say they have a penicillin allergy. Patients with penicillin allergy labels are at risk of longer hospital admissions, more complications, and are more likely to be infected with an antibiotic-resistant bug like MRSA. However, if assessed, up to 90 per cent of these people can safely take penicillins.

There are many reasons for this discrepancy, and when patients are assessed for their penicillin allergies there are a few questions that come up that can explain why:

What actually is penicillin allergy?

Allergies are immune system mediated hypersensitivities to a substance that is normally considered benign.

Immediate allergy (also called immediate hypersensitivity) are reactions that occur within an hour of taking a dose of penicillin. These reactions cause symptoms like hives, swelling, itch, breathing difficulties or, in the most severe cases, anaphylaxis.

There is also delayed allergies (delayed hypersensitivity) where you developed a flat reddish-purple rash (called a maculopapular rash) within a couple of days of starting a course of antibiotics.

Why could my penicillin allergy label be wrong?

Allergy is a type of adverse reaction. Adverse reactions are any bad or unpleasant outcomes of taking a medication. These are sometimes anticipated side effects, such as nausea or diarrhoea when taking an antibiotic. Though unpleasant these are NOT allergies, and we can manage these side effects either by changing how we take the antibiotic or how often we take it.

Sometimes, particularly in young children, viral rashes can mimic the rash seen in delayed hypersensitivity. If a child is taking antibiotics at the same time this can be mistaken for an allergic reaction.

Can I outgrow my penicillin allergy?

It is estimated that 50 per cent of people with a penicillin reaction will no longer be allergic five years after their reaction, and 80 per cent will no longer react ten years after their reaction. If you had a mild rash to penicillin as a child, you may be able to take it as an adult.

My mum had a penicillin allergy- should I avoid it too?

With other allergic diseases such as food allergy, eczema, hay fever or asthma we can see it run in families. The same is not true for penicillin allergy, so you do not need to avoid penicillins if you have a family member who has a penicillin or other antibiotic allergy.

How do I know if I can really take penicillin or not?

If you have been labelled as penicillin allergic and are unclear on what it means for you and what your options are it is worth speaking to your GP. After taking a history they may determine that it is safe for you to take penicillins. They can also refer you for assessment with an immunologist who can arrange for more in depth testing to determine what antibiotics you can safely take.


Authored by Dr Jacqueline Loprete, Clinical Immunologist at St Vincent's Clinic.