Penicillin allergies are frequently mislabelled, resulting in unnecessary broad-spectrum antibiotic use and extended hospital stays. At London North West University Healthcare NHS Trust, a team has implemented a pharmacist-led inpatient delabelling service that safely removes inaccurate allergy labels through direct oral challenges. Here, they describe how this approach optimises treatment, enhances patient outcomes and strengthens antimicrobial stewardship.
Penicillin allergy is one of the most frequently reported drug allergies in hospitalised patients, yet the majority of these labels are inaccurate. Studies have shown that 10% of the general population reports having a penicillin allergy, and over 85% of patients labelled as allergic are not truly allergic when formally tested. Additionally, up to 99% of low-risk cases can be safely delabelled through direct oral challenge.1–4 Mislabelled allergies lead to the use of broader-spectrum, more toxic and less cost-effective antibiotics, contributing to antimicrobial resistance and prolonged hospital stays.
To address this, London North West University Healthcare NHS Trust (LNWUH) developed a non-allergist-led penicillin allergy testing service. It was initially launched in outpatient settings in 2017 and expanded to inpatient wards in 2021 and is going from strength to strength.5
Designing and delivering a penicillin allergy delabelling service
The inpatient penicillin allergy delabelling service was introduced to optimise antimicrobial therapy and reduce unnecessary intravenous (IV) antibiotic use. The service targets patients with low-risk allergy histories: those who either cannot recall their reaction or report mild, non-anaphylactic symptoms such as rashes or gastrointestinal upset; unknown childhood reactions; or distant reactions that occurred more than 10 years earlier.
The simplified inpatient protocol, approved by the hospital’s Drugs and Therapeutics Committee, allows pharmacists to conduct direct oral challenges for penicillin allergy under the oversight of infectious diseases physicians. This approach aligns with national and international evidence supporting the safety of oral challenges in low-risk patients.3,4
Patients are informed about the procedure and provide consent before testing begins. Eligible inpatients then undergo a two-step oral challenge using co-amoxiclav (amoxicillin/clavulanate). The first step involves administering a 50 mg amoxicillin-equivalent dose, followed by a second 500 mg amoxicillin-equivalent dose 30 minutes later.
Patients are monitored for one hour following the oral challenge. If no adverse reaction occurs, the penicillin allergy label is removed, the allergy status is updated on the electronic prescribing and medicines administration system and the patient may be switched to a penicillin-based antibiotic regimen. A day-three follow-up is conducted to check for any delayed reactions.
For patients not requiring penicillin-based treatment for an active infection, a three-day course of co-amoxiclav is prescribed to complete the delabelling process. The patient’s GP is notified of the updated allergy status through the discharge summary or letter.
A real-world example of successful penicillin allergy delabelling
A 64-year-old male patient with a reported amoxicillin allergy – described as ‘hot flushes’ experienced over a decade ago – was admitted with a diabetic foot infection. He was initially treated with ceftriaxone 2 g IV once daily and metronidazole 400 mg orally three times a day. Following review, the microbiology consultant, in collaboration with the medical team, referred the patient to the anti-infective pharmacy team for allergy testing.
After a thorough review and confirmation of eligibility, the patient provided consent and underwent inpatient testing in accordance with the Trust’s standard operating procedure. The penicillin allergy oral challenge was carried out using co-amoxiclav 250/62.5 mg/5 mL liquid, administered in two split doses: an initial 1 mL dose (equivalent to 50 mg amoxicillin), followed by a 10 mL dose (equivalent to 500 mg amoxicillin) after 30 minutes. No adverse reactions were observed during the subsequent one-hour monitoring period.
With no signs of allergy, the patient’s penicillin allergy label was removed, and his antibiotic regimen was simplified to co-amoxiclav 625 mg orally three times daily. This adjustment enabled the discontinuation of IV therapy, facilitated earlier hospital discharge and contributed to a better overall patient experience by reducing the number of bed days.
Conclusion
This case report exemplifies the clinical and operational benefits of inpatient penicillin allergy de-labelling. By identifying patients with low-risk allergy histories and safely testing them during admission, LNWUH has strengthened antimicrobial stewardship, enhanced patient care and reduced healthcare costs.
The service showcases how pharmacist-led initiatives, supported by multidisciplinary collaboration, can effectively address widespread clinical challenges. This model offers a scalable solution for other NHS Trusts aiming to address the burden of mislabelled penicillin allergies.
Authors
Cassandra Watson MPharm ClinDipPharm IPresc MSc
Lead anti-infectives pharmacist, antimicrobial stewardship/infectious diseases and HIV services
Shiv Shah MPharm PGDIP IPresc
Specialist anti-infectives pharmacist, HIV
Krishan Bhovan MPharm PGDIP IPresc
Specialist anti-infectives pharmacist, virtual ward service
All of London North West University Healthcare NHS Trust
References
1 Apter AJ et al. Represcription of penicillin after allergic-like events. J Allergy Clin Immunol 2004;113:764–70.
2 Co Minh HB et al. Systemic reactions during skin tests with beta-lactams: a risk factor analysis. J Allergy Clin Immunol 2006;117:466–8.
3 Trubiano JA et al. Impact of an integrated antibiotic allergy testing program on antimicrobial stewardship: a multicenter evaluation. Clin Infect Dis 2017;65:166–74.
4 Koo G et al. Low-risk penicillin allergy delabeling through a direct oral challenge in immunocompromised and/or multiple drug allergy labeled patients in a critical care setting. J Allergy Clin Immunol Pract 2022;10:1660–3.
5 Watson C et al. From the clinic to the wards, the evolution of penicillin allergy testing by non-allergists in a UK hospital. J Hosp Infect 2025;155:158–60.
