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This page will give you information about what penicillin is, what a penicillin allergy is and how you can be tested. A member of staff will speak to you about everything on this page, but if you have any questions, please ask us.

A penicillin is an important type of antibiotic that can be used to treat many common infections. Penicillin antibiotics are often the first-choice antibiotic for common infections like pneumonia, skin infections and tonsillitis. They are widely used both in hospital and in the community.

A penicillin allergy occurs when the body’s immune system responds unusually to a penicillin-type antibiotic.

Examples of penicillin antibiotics include:
Amoxicillin Co-amoxiclav (Augmentin)
Flucloxacillin Phenoxymethylpenicillin (penicillin V)


For most people, an allergic reaction will be an unpleasant mild skin reaction or rash that develops slowly after several hours or days of taking the medicine. Sometimes a more severe reaction can occur called anaphylaxis. Anaphylaxis is extremely rare but can be life-threatening.

People with anaphylaxis develop symptoms such as a widespread itchy rash (like nettle sting), breathing difficulties, swelling and collapse very quickly, often within minutes of taking penicillin and always within two hours.

All medicines may cause unpleasant side effects such as skin reactions/rash, vomiting or diarrhoea. Side effects are different to allergic reactions. Having side effects to penicillin, whilst unpleasant does not mean you need to avoid penicillin antibiotics completely. This is particularly true in severe infections where penicillin may be the best antibiotic. In these situations, it is often best to receive penicillin and manage side effects if they happen.


Penicillins are very effective treatments for many infections including skin and chest infections. They are also commonly used in patients having a surgical procedure. Being unable to take penicillins may put you at a disadvantage especially if you are admitted to hospital with a severe infection.

We can carry out a simple test within the hospital that will tell you if you have a penicillin allergy. If your test results show that you are not allergic to the test penicillin then your medical records will be updated. Amending the penicillin allergy label on your record means you can be given the tested penicillin when you really need them. It also means you will have more treatment options if you have an infection or require antibiotics before an operation.

A member from the Penicillin allergy de-labelling team will first ask you about your penicillin allergy, the problems you had when you took a penicillin antibiotic, and when the problem happened. Many people won’t know the answers to these questions, which is fine. You will only be offered this test if the medical team believe that it is safe to do so and there is a very low chance of an allergic reaction.

You will be asked to sign a consent form before your test, to confirm you understand what the test involves, potential risks and side effects and that you agree to have it. You will be tested to the penicillin that caused your reaction, or if you don’t know what that was amoxicillin will be used, because this is the most commonly prescribed penicillin. You will be given a small oral dose of a penicillin syrup (1/10th of the normal dose) to start with, and gradually increase the amount over time until you reach the normal dose, or until an adverse effect or reaction occurs.

To ensure you are well on the day we will check your blood pressure, pulse and oxygen levels. None of these tests will hurt. We will check these before commencing the test and after you take each test dose. After the last dose, you will be monitored for another hour. If you do have a reaction, you will be immediately given treatment with anti-allergy medicines to stop it. All tests are done under close supervision, and you will be carefully monitored at all times.


There is a risk of reaction during challenge testing and this is why the test is done in a hospital. The team will discuss this with you before deciding to do the test. If you do start to react then medicines (such as antihistamines, steroids or adrenaline) will be given to treat the symptoms and stop the reaction from progressing. The challenge will then be terminated.

Please bring a list of any medicines you are currently taking, including medicines you have bought yourself or alternative medicines, such as herbal remedies. If you are taking antihistamine tablets (treatment for allergy), please stop taking them three days before your test. Similarly, if you are taking a beta-blocker for high blood pressure (such as bisoprolol) or inhalers for asthma inform the penicillin allergy team for advice about when to stop these medicines, as they may interfere with the test. Also, please let us know if you are pregnant.

We advise that you eat a good breakfast on the day, as you will have to stay within the clinical area once the test commences. You may wish to bring something to pass the time such as a book or magazine.

In general, any symptoms of allergy are noticed during the test and will be treated immediately. If you are allergic to the penicillin being tested, you may develop symptoms that are similar to those that you experienced last time. However, we expect them to be much milder as we start the challenge with very small doses. Other symptoms may include itchy or swollen skin, a rash, a hoarse voice or dizziness. In exceptional circumstances, symptoms may progress to palpitations, abdominal pain, difficulty in breathing, and hypotension (low blood pressure, which causes dizziness). You will immediately receive emergency treatment to stop the reaction.

It is rare for a reaction to occur after you have left the hospital. If you have any of the symptoms listed above completing the test, either email the penicillin de-labelling team (using the contact details given below) or if you have severe symptoms visit your local A&E department.

If you have not experienced any reaction, a letter will then be sent to your GP informing them of the result of the test. Your GP will be asked to update the penicillin allergy label on your GP record. We will also give you information explaining the results and what they mean for your future care. If you need an antibiotic now or in the future for either treatment or before surgery, then your doctor will have the option to use the tested penicillin antibiotic. If the test confirms that you are allergic to penicillin, then we will advise your GP of the test result and ask them to record this in your GP record. We will also give you information about avoiding penicillin in future.

A member of the team will assess you at five days after the test to confirm whether you have had any symptoms which may indicate that you had a delayed allergic reaction. This will be done via telephone consultation.

UK Anaphylaxis Campaign

tel: 01252 542 029 w:

NHS Direct

tel: 0845 4647 w:

NHS Choices

Allergy UK

British Society for Allergy & Clinical Immunology

Switchboard: 020 3456 7890


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