Immunology - Penicillin Allergy Testing

Penicillin allergy facts

Penicillin based antibiotics are widely used antibiotics and have an important role in treating bacterial infections. Many patients are diagnosed with penicillin allergy in childhood, where for example a viral infection may be the cause of a rash, rather than a drug reaction.

Approximately 10% of the population reports a penicillin allergy, but most of these individuals will be able to tolerate penicillin.
Penicillins are the safest and most effective antibiotics for many infections. Therefore it is important to find out if you are really allergic to Penicillin.

Like all medicines, these antibiotics can have side effects (e.g. nausea, vomiting), this is not allergy. Penicillins can also cause delayed allergy symptoms.

Penicillin allergy investigation

Penicillin allergy can be investigated by an Allergy or Immunology service, who will obtain a careful history and perform allergy procedures, such as skin testing and/or a challenge test if indicated.

Penicillin skin testing is indicated in patients with history of an immediate reaction including symptoms of hives, itching, rash, swelling, shortness of breath, and/or low blood pressure; symptoms suggestive of immediate (type 1) allergic reaction.

Blood tests may be performed to investigate if your body has produced an allergy response to penicillin antibiotics. This test is not entirely reliable and does not help to confidently rule out penicillin allergy.

Penicillin skin testing

This test involves pricking the skin with various types of penicillin and its components, and subsequent intradermal test (injecting a small amount of diluted forms of penicillin just under the skin). If these tests are negative, it is very unlikely that you are allergic to penicillin.

However, a challenge test to penicillin is required to confidently rule out your risk for an immediate reaction to penicillin.

Penicillin challenge test

If a patient’s history is very low risk and does not sound typical of allergy or the skin prick testing and intradermal testing is negative, a challenge test with penicillin may be required.

This involves giving you increased doses of penicillin with careful monitoring (physical observations and peak flow) in a day unit.

A cannula is inserted into a vein in your arm in case we need to give you medication to treat immediate allergy symptoms as described above.

If you tolerate all doses of the penicillin during the challenge test, an extended course of penicillin will be given to you to take at home to exclude delayed reactions and to confirm you can tolerate a short course without significant side effects.

If the full dose is tolerated, the patient is not at risk of having a serious immediate reaction and penicillins can be used.

Challenge tests usually take about 4-5 hours in case of uneventful reactions.

Penicillin allergy confirmed

In case of a positive penicillin test, either the skin prick or intradermal test will produce a red, raised small lump, signifying the presence of an allergy to the medication.

If skin testing or the challenge test were positive, an alternative non-penicillin antibiotic should be used to treat an infection.

Frequently asked questions

What is penicillin?

Penicillin was first discovered by Alexander Fleming in 1928. It continues to be one of the most important and frequently used classes of antibiotics in the world today.

The penicillin family of antibiotics contains over 15 chemically related drugs (e.g. penicillin, ampicillin, amoxicillin, Co-amoxiclav, Flucloxacillin, Tazocin) that are given by mouth or injection for the treatment of many bacterial infections.

Is penicillin allergy genetic?

Although some forms of drug allergy may be genetic, there currently is no predictable pattern to inheritance of penicillin allergy.

Individuals do not need to avoid penicillin if a family member is allergic to penicillin or drugs in the penicillin family.

Why would I need penicillin allergy testing?

To confirm or rule out immediate type of penicillin allergy. Depending on your clinical history, Penicillin Skin Prick Testing may be indicated for you.
 
Research has shown that penicillin allergies may be over- reported. Therefore, accurate diagnosis is needed to ensure the best treatment options in future.

What is skin prick testing and what is involved?

Penicillin testing is a three-step process. A blood test is usually the first step. This is followed by skin testing. It is usually not painful.

Skin prick testing uses small lancets that barely penetrate the skin’s surface. There should be no more than mild, momentary discomfort.

Intradermal skin testing is the second part of the evaluation and involves injecting a small amount of solution under the skin. This test can be uncomfortable with a slight sting initially.

If you do develop a rash at the site of testing in the following 24-48 hours, we suggest you take a photograph and inform us.

The test, if positive, will cause local itching and redness with swelling at the site where the test is performed. These reactions usually resolve in an hour or so.

What alternative antibiotics can I take if I am allergic to penicillin?

There are many antibiotics that do not include penicillin. Some examples are erythromycin, clarithromycin, doxycycline etc.

Contact details

Division of Surgery & Tertiary Medicine, Turnberg Building, 2nd Floor, Salford Royal Hospital, Stott Lane, Salford, M6 8HD.
Tel: 0161 206 0522

Immunology/Allergy Clinical Nurse Specialists - 0161 206 5576 (8am to 4pm excluding bank and public holidays).

Email: Salfordimmunology.nurses@nca.nhs.uk