Introduction: Necrotising otitis externa (NOE) is a serious, progressive infection of the external ear canal. If untreated, it can invade into temporal bone, skull-base and surrounding tissue resulting in cranial nerve palsies, neurological infections and death. Patients present with unremitting, severe otalgia, otorrhoea and oedematous ear canals containing granulation. Surgery has a limited role; the mainstay of treatment involves a long course of intravenous antibiotics. Currently, there is no data on the complications of antibiotic treatment for NOE. This project aims to provide evidence on the nature/frequency of severe treatment-related complications requiring a change in antibiotic regime. Methods: A retrospective 5-year cohort analysis was performed on 64 patients who were treated for confirmed NOE with intravenous antibiotic therapy. Clinical notes, blood results and antibiotic prescriptions were documented and analysed. Results: Average duration of treatment was 11 weeks (range=38 weeks). There was an average of 2.1 antibiotic regimes per patient with 10 cases requiring inpatient admission due to treatment-related complications. 63% of treatment changes were directly related to adverse effects of intravenous antibiotics. Drug allergy/intolerance (n=18) and clinical deterioration i.e. Lack of symptomatic improvement and/or worsening inflammatory markers (n=18), were the most common reasons for antibiotic change. Neutropenia, deranged liver function tests and acute kidney injury were also recognised adverse effects of treatment. Conclusion: This study provides the first evidence on the notable frequency of antibiotic-related complications in NOE patients. Larger, multicentre studies are required in the future to validate our findings and will better inform both clinicians and patients of the risks of treatment.