22nd September 2020

If a patient has a penicillin allergy record in their medical notes, every doctor knows what to do. We avoid the more narrow-spectrum penicillin antibiotics in these patients and instead use second line antibiotics which often have a broader spectrum, right? But what if in doing so, we are doing more harm than good?

Approximately 15% of hospital inpatients have a penicillin allergy record in their medical notes, which means we avoid the more narrow-spectrum penicillin antibiotics in these patients and instead use second line antibiotics which often have a broader spectrum. We avoid penicillin in these patients for reasons of safety; if a patient has a penicillin allergy record then penicillin is avoided due to concerns about the potential for a future allergic reaction. Paradoxically the opposite may be true. Ninety five percent of patients with a reported penicillin allergy record can in fact tolerate penicillin. The reactions people report to penicillin are due to a multitude of reasons. For example, many rashes experienced by patients while taking penicillin are viral or bacterial associated rashes, or the symptoms reported may be a common side effect of penicillin such as diarrhoea or thrush, or the reported symptoms may indeed have been a genuine allergic reaction but 80% of people grown out of the allergy after 10 years. So, if the allergic reaction occurred a long time ago then the allergy to penicillin may have been lost. But, this is complicated by the fact there remain a small number of patients with genuine allergic reactions and in some people re-exposure to penicillin may result in a life threatening reaction, such as anaphylaxis.

Identifying patients with penicillin allergy records that are not genuine allergies through appropriate testing, and removing the allergy record if safe to do so, is called de-labelling.  Giving those patients penicillin instead of the broader spectrum alternative antibiotics would contribute to the UK’s 5 year strategy to reduce AMR. This is because broad spectrum antibiotics are more likely to exacerbate the antibiotic resistance problem compared to narrower spectrum antibiotics, as broad spectrum antibiotics are able to drive antibiotic resistance in a wide range of different bacteria whereas narrower spectrum antibiotics only have potential to drive resistance is a small number of bacteria.

There are other potential benefits to using narrower spectrum penicillin over broader spectrum antibiotics. The use of broader spectrum antibiotics used in patients with penicillin allergy are associated with many unintended patient and health system outcomes which include: longer length of hospital stays, increased risk of side effects, increased risk of Closteroides difficile-associated diarrhoea, MRSA infection, treatment failure, death, increased antibiotic spend, higher admission rates to critical care, and higher hospital re-admission rates.

However, a note of caution should be sounded. If removing incorrect penicillin allergy labels will allow us to give more narrow-spectrum antibiotics this will undoubtedly help to reduce rates of resistance. However, more research needs to be conducted in order to explore if removing these incorrect allergy records reverses the associated unintended patient harm and health system consequences associated with use of wider-spectrum antibiotics, while also not risking allergic reactions in these patients. Research in the UK, and elsewhere, exploring how we safely remove incorrect penicillin allergy labels is ongoing, and nationally, allergy experts are figuring out how we safely do this in UK hospitals.

Neil Powell is consultant antimicrobial pharmacist at Royal Cornwall Hospitals NHS Trust

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