Background
- Most patients who say they have a penicillin allergy are not allergic to penicillin. While 10% of the population will report a penicillin allergy, less than 1% will be truly allergic. They have been erroneously labelled as penicillin-allergic.
- The patient may have had a non-immune-mediated reaction such as nausea and vomiting, an exanthema (e.g. after taking amoxicillin during an Epstein-Barr virus infection) or an injection-site reaction
- Penicillin allergies are not always lifelong. Approximately 50% are lost over five years and 80% over 10 years. A reaction to penicillin during a childhood infection is unlikely to be a true allergy
- Only 1–2% of patients with a confirmed penicillin allergy have an allergy to cephalosporins. In patients with a low risk of severe allergic reactions, cephalosporins are a relatively safe treatment option
- Patients with a history of delayed non-severe reactions, such as mild childhood rashes that occurred over 10 years ago, may be suitable for an oral rechallenge with low-dose penicillin.
- This should be done in a supervised hospital environment In many cases, with appropriate assessment and allergy testing, it may be possible to remove the penicillin allergy label
- Allergic reactions to B-Lactam antibiotics are the most frequently encountered immunologically mediated adverse drug reaction. Up to 17% of the population report an allergic reaction to penicillin the nature and severity of which may be difficult to determine.
- Studies have shown patients labelled as penicillin allergic are more likely to receive drugs that are more costly, broader spectrum and have the potential for more adverse reactions (including Clostridioides difficile infection) and induction of antimicrobial resistance
Taking a History of Penicillin Allergy: What to ask
- What antibiotics has the patient reacted to in the past?
- What antibiotics has the patient taken and tolerated since the allergy diagnosis (in particular penicillin or cephalosporins)?
- When did the reaction take place (estimated date)?
- What was the nature of the reaction (eg. diarrhoea, rash, swelling, difficulties breathing etc.)?
- If rash then: Describe nature of rash (eg. maculo-papular, pustular, bullous, urticarial etc.)
- Could this rash be related to the underlying condition (eg. viral rash, meningococcal sepsis etc.)?
- Could the rash be related to interaction with other medication? How long after commencing the antibiotic did the rash appear?
- Why was the patient taking the antibiotic?
- Did this reaction result in hospitalisation or movement to a High Dependency Unit/Intensive Care Unit if already an in-patient?
- Did the reaction resolve on cessation of the antibiotic?
- To find this information speak to the patient or carer, the GP and look in the patients notes.
Assessment
- As a patient safety feature, all antibiotics are colour coded to aid the prescriber to distinguish between penicillins (a subclass of beta-lactams) in which case they cannot be given in known penicillin prophylaxis
- Other beta lactams (cephalosporins and carbapenems) which might be given in a patient with minor penicillin allergy under caution and non-beta-lactam related antibiotics that can be given regardless of the penicillin allergy status of the patient.
Coding
- RED - all penicillin, these should not be given to a known penicillin allergic patient.
- Amber - other beta-lactams (Penicillin related) which might be given to a patient with minor penicillin allergy with caution
- Green - All non-beta-lactam related antibiotics that can be given to penicillin allergic patients regardless of the nature of allergy
- The colour coding of antibiotics in the guidelines are summarised below
