Do I have a penicillin allergy?

What is penicillin?

The penicillin family of antibiotics are used to treat common bacterial infections such as tonsillitis, pneumonia and skin infections.

Why is penicillin important?

Penicillin can work better than other types of antibiotics to treat bacterial infections. It is therefore very important to know if you are allergic to penicillin. This will make sure that you are given the best antibiotic for your infection.

What is an allergy to penicillin?

An allergy is a reaction of your body’s immune system. The immune system can react to penicillin or to another penicillin-type of antibiotic such as amoxicillin, co-amoxiclav, flucloxacillin and phenoxymethy penicillin. For most people, the allergic reaction is a mild skin reaction or rash that develops slowly over several hours or days after taking penicillin.

Sometimes a severe allergic reaction called anaphylaxis can happen. This is very rare but it can be life-threatening. Symptoms of anaphylaxis include a rash that spreads fast, swelling of the mouth, throat or tongue, and breathing difficulties. These symptoms will normally happen within an hour after taking penicillin.

What if a family member is allergic to penicillin?

Penicillin allergy does not run in families. If you have a relative who is allergic to penicillin, there is no reason to think that you will also be allergic to it.

What is the difference between an allergy and side effects?

All medicines can cause unpleasant side effects such as minor skin reactions/rash, vomiting or diarrhoea. Side effects are different to allergic reactions. Having a side effect to penicillin, while unpleasant, does not mean you need to completely avoid penicillin antibiotics. This is particularly true in severe infections where penicillin may be the best treatment.

How common is an allergy to penicillin?

Around 1 out of every 10 people report having an allergy to penicillin. However, evidence suggests that more than 9 out of 10 people who report an allergy to penicillin might not be allergic to the medication. They may have had side effects from taking penicillin.

About 1 in every 100 people have a genuine penicillin allergy. The most severe allergy, anaphylaxis, happens in about 1 in every 10,000 people taking penicillin. This means that a severe allergy is rare.

I have had a recorded penicillin allergy for a long time - why should that change now?

Penicillin is a very effective treatment for many bacterial infections of the skin and chest. Penicillin is also commonly used for patients having a surgical procedure.

It is essential to know whether you are truly allergic to penicillin, or not, in order for you to receive the most appropriate and safest treatment for your infection in the future.

What are the benefits of finding out whether I am allergic to penicillin?

Removing the penicillin allergy label from your record means you can be given penicillin antibiotics 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.

What does the test for a penicillin allergy involve?

Before the test, your medical team will ask you about the symptoms you had in the past that led to the penicillin allergy label. The team may decide that you could have been incorrectly recorded as having an allergy.

You may then be offered a test to confirm if the allergy label can be removed from your records.

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.

The test will involve giving you a penicillin antibiotic tablet or capsule. This will be done under careful supervision in hospital. Your pulse and blood pressure will be monitored for 1 hour after you have taken the tablet or capsule.

Results of the test

At the end of the test the hospital team will discuss with you what your test results mean.

If you have not experienced any reaction and the test confirms that you are not allergic to penicillin, a letter will then be sent to your GP informing them of the result. Your GP will be asked to remove the penicillin allergy label from your GP record.

We will give you information to take home explaining the results of the test and what it will mean for your future care. If you need an antibiotic in the future for either treatment or before surgery, then your doctor will have the option to give you penicillin.

Is it essential to have this test?

The benefits of having the test have already been explained on this page. If you do not want to be tested, please let the medical team know. Your decision will not affect your continuing or future care or treatment.

What are the risks or side effects of the test?

There is a small chance that you may experience an unpleasant side effect such as nausea or an allergic reaction. Allergic reactions will usually be mild but a severe allergic reaction including anaphylaxis, although highly unlikely, is possible.

You will be closely monitored during the test by staff trained in the recognition and treatment of allergic reactions and other side effects.

In the unlikely event you experience a severe allergic reaction, the medical team will give you treatment to reverse this.

What will happen if I agree to have the test?

One of the medical team will ask you to read and sign a consent form. By signing the form, you are agreeing to have the test. The doctor will also sign this form and it will be held in your medical notes as a record of your agreement to the test.

What will happen if I decide not to have the test?

If you do not have the test then your medical notes will continue to state you are allergic to penicillin and you will not be given penicillin when you are treated for an infection or have a surgical procedure in the future.

You can re-consider having the test at any time.

Acknowledgement

The information on this page has been adopted with permission from:

Healthcare Improvement Scotland SAPG October 2021

All Wales Medicines Strategy Group

Cardiff and Vale Penicillin Allergy De-Labelling Group

All Wales guidance for penicillin allergy de-labelling in adults in secondary care July 2024