Monitoring ethambutol-induced optic neuropathy

Background

Ethambutol-induced optic neuropathy poses a significant risk to patients, potentially leading to irreversible vision loss. Timely monitoring of visual acuity and colour discrimination is essential for early detection of symptoms and allows for prompt treatment cessation to reduce the risk of visual impairment. To understand current practice at Leeds Teaching Hospitals NHS Trust (LTHT) an audit was undertaken to identify where standards of care relating to ethambutol monitoring are not met and identify what interventions can be implemented to improve patient safety.

Audit standards

100% of patients should have:

1. Visual testing documented prior to treatment.
2. Prescriptions dosed correctly according to renal function.
3. Symptom screen documented where creatinine clearance is ≥30ml/min.
4. Additional monthly visual testing documented where creatinine clearance is <30ml/min.

The audit standards align with the recommendations outlined in TB drug monographs, a recognised resource to support monitoring and safe use of anti-tuberculosis drugs.

Method

Using reports from the JAC dispensing system, a list of inpatients dispensed ethambutol tablets and oral solution, and Voractiv^® tablets between 1 January 2023 and 21 August 2023 was generated. Clinical notes for each patient were reviewed to extract data on visual monitoring and assess renal function. Ethambutol regimens were extracted from JAC. Microsoft Excel was used to store extracted data and measure against the audit standards. This audit did not require ethics approval.

Results

Fifteen patients were identified, with 47% (n=7) of patients having baseline visual testing documented on the day of or before initiating ethambutol, highlighting substandard practice. There were no cases of ethambutol discontinuation when patients had baseline assessments performed after ethambutol initiation (n=2). All prescriptions were dosed correctly for renal function.

Five patients transferred to other NHS trusts post- treatment initiation were excluded from the assessment of standards 3 and 4. Of the assessable patients, 90% (n=9/10) had appropriate monitoring documented. The one patient who did not meet standards 3 and 4 had a creatinine clearance <30ml/min was palliated; further monitoring was not indicated.

Conclusions and recommendations

Despite no confirmed cases of ethambutol-induced optic neuropathy being documented, the lack of adherence to standard 1 is concerning given the direct impact on patient safety. Previous reports have indicated variations in practice across England, and it is recommended that other Trusts audit their practice as non-adherence to standard 1 is likely to be a universal finding.

A limitation of the audit was the small sample size. Future goals include expanding the audit to include outpatients and collaborating with other hospitals where patients have been transferred.

This audit emphasises the need for consistent and comprehensive monitoring guidance for ethambutol-induced optic neuropathy for inpatients and highlights the need for further large-scale audits to understand current clinical practice within LTHT.

Additional authors: Thomas Bennett

The opinions expressed in this article are those of the author. They do not purport to reflect the opinions or views of the UKCPA or its members. We encourage readers to follow links and references to primary research papers and guidance.