Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease with a median survival of 3-5 years. While the antifibrotic drug pirfenidone is known to decrease decline of lung function in IPF patients, it is also associated with adverse gastrointestinal and skin-related events. Although some studies suggest low-dose pirfenidone is non-inferior to standard dosing, the burden of adverse side effects in low-dose pirfenidone is not well-known. Therefore, this single-centre study based in South Korea aimed to elucidate the factors associated with pirfenidone dose reduction. The study population consisted of IPF patients treated with pirfenidone, with 1 or more follow-up visits that assessed for adverse side effects. In this study, a standard dose was considered 1800 mg/day, whereas low-dose was less than 1800 mg/day. In total, there were 156 patients included, with a mean age of 69.7 years, and a median (IQR) follow-up of 243 (84-385) days. The study found that those taking low-dose pirfenidone were more likely older (71.0 years vs 67.4 years, p = 0.016), less likely to be ever-smokers (80.8% vs 96.4%, p = 0.008), and more likely to have a lower BMI (24.1 kg/m2 vs 25.7 kg/m2, p = 0.027). There were no differences in pulmonary fit test results, exercise capacity, or rates of pulmonary hypertension between the standard and low-dose groups, though more patients on standard dosing had emphysema (p = 0.048). After adjusting for sex, BMI, smoking status, and emphysema, older age was associated with reduction of pirfenidone dose (OR 1.066, p = 0.016). In addition, there were higher rates of some adverse events reported in the low-dose compared to the standard dose group, including anorexia (20.5% vs 3.5%, p = 0.004), urticaria (24.7% vs 10.5%, p = 0.039), and generalized weakness (9.6% vs 0.0%, p = 0.018). More broadly, the low-dose group experienced higher rates of gastrointestinal side effects (p < 0.01) and skin side effects (p = 0.020) than the standard group. Overall, this study demonstrated that older patients were more likely to be on low-dose pirfenidone, and that individuals in the low-dose group were more likely to experience side effects, though there were no differences in pulmonary function and efficacy of pirfenidone between the groups.
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