Background: Guidance recommends regular monitoring of liver enzymes when patients are prescribed nintedanib and pirfenidone, monthly for the first 3 and 6 months, respectively, then 3 monthly thereafter. All patients prescribed antifibrotic therapy at our ILD specialist centre in England have followed this monitoring schedule but the impact is unknown. This study aims to assess the impact of regular blood monitoring on patient safety when prescribed antifibrotic therapy.

Methods: A retrospective analysis assessed patients who had liver enzyme derangement above 3 times the upper limit of normal, as per guidance, and the actions necessary to manage this.

Results: 454 patients were prescribed antifibrotic therapy March 2015 to January 2023 and all patients had monitoring as per guidance. Ten patients (2.2%) had liver enzyme derangement above 3 times the upper limit of normal. All 10 of these patients presented with symptoms such as fatigue, appetite and/or weight loss which prompted repeat blood test. Of the 10 patients, 4 stopped therapy due to intolerance, 4 re-trialled with no further liver enzyme derangement and 2 switched to alternative. Liver function tests cost £2.81 at our institution. Patients remained on therapy for an average of 15 months and monitoring per schedule required 3788 blood tests, costing a total of £10,644 and 1894 hours of clinical time, based on 30 minutes per test (excluding environmental and financial cost of patient travel).

Conclusions: No patients were found to have asymptomatic liver enzyme derangement. Targeted and responsive monitoring may be safe and minimise healthcare demands.