Patient Experience

Patient Experience

Penicillin Allergy Patient Information

Penicillin allergy is an unexpected reaction to a medication that is mediated by the immune system. This typically causes a rash, but sometimes can make you very unwell. Penicillin allergy does not refer to expected side effects of medication, such as stomach upset. Penicillin allergy is reported by more than 12% of Irish healthcare users. However, the majority of people that think they have penicillin allergy can actually take penicillin safely. This means that they may be avoiding a useful drug for no reason.

  • Penicillin allergy testing allows hypersensitivity reactions to penicillin to be diagnosed or ruled out. This may allow you to be treated with penicillin which is a very effective treatment for many infections.

    Additionally, patients that can take penicillin have lower levels of resistant infections and even have shorter hospital stays, on average.

  • Drug allergy testing typically involves 4 steps:

    1. You will be assessed by the immunology doctor to determine suitability for testing. Skin testing is not appropriate for all forms of penicillin allergy – for example, skin testing does not provide information on delayed drug reactions.
    2. Skin prick testing – the skin is scratched with a solution of the suspect medication and related medications. Typically 8 test solutions are required. A positive test results in a small hive.
    3. 'Intradermal' testing – a small amount of the drug is injected into the skin. This can be painful.
    4. Diagnostic challenge testing – you will be given the suspect drug and observed for an allergic reaction. This is considered an essential part of the testing process. It is to be expected that a small number of people will develop allergic symptoms, even when skin tests are negative. These symptoms are usually mild but can be severe on occasion. The development of allergic symptoms indicates a positive diagnostic challenge. In order to proceed with assessment you should be prepared to undergo diagnostic challenge testing and be aware that there is a risk of allergic reaction.
Positive intradermal tests in a patient with penicillin allergy

  • The testing process may take between 3 and 8 hours, depending on the number of tests required. You may be required to attend on several occasions to complete the test. In some cases, an extended diagnostic challenge for up to 5 days may be required.

  • No, this is not possible. The available tests are not suitable for screening

  • Skin testing for penicillin allergy can be a little uncomfortable and itchy. Serious reactions to skin testing are very rare.

  • Diagnostic challenge testing is carried out after skin tests are negative. When skin tests are negative the risk of reaction is low, but, allergic reactions do occur – this is why the diagnostic challenge test is carried out.

    These reactions are usually mild but on occasion can be serious or even life threatening, with long term consequences. However, major problems are very uncommon,

    Very rarely you can become allergic after having a negative diagnostic challenge. This is very uncommon.

    The medical team can treat most allergic reactions in the unlikely event of problems.

  • Unfortunately waiting times are very long for this service. We are continuing to work to improve the availability assessment for medication allergy. In addition, testing is currently restricted, in line with NICE guidance.

  • If you decide not to proceed with testing you can discuss this with your doctor.