A Phase I Evaluation of the Safety and Tolerability of Pirfenidone in Idiopathic Subglottic Stenosis

Idiopathic subglottic stenosis (iSGS) is a progressive fibro-inflammatory airway disease characterized by recurrent scarring and narrowing of the subglottic and upper tracheal airway in otherwise healthy adults, predominantly women. Current management relies on repeated endoscopic dilations and serial intralesional steroid injections, which temporarily restore airway patency but are not curative and are associated with high rates of restenosis and substantial symptom burden. Molecular and single-cell transcriptomic studies from the Canadian Airways Research (CARE) Group biobank have demonstrated a fibrotic gene expression signature in iSGS, with transforming growth factor (TGF)-mediated fibroblast activation and extracellular matrix deposition that closely parallels idiopathic pulmonary fibrosis (IPF).

Pirfenidone is an oral antifibrotic agent approved for IPF that inhibits TGF-driven fibroblast proliferation, collagen synthesis, and profibrotic cytokine release and has an established long-term safety profile in chronic fibrotic lung disease. On this mechanistic basis, pirfenidone is being repurposed as a potential disease-modifying therapy for iSGS. This multi-centre, randomized, double-blind, placebo-controlled Phase I trial will evaluate the safety, tolerability, and preliminary efficacy of pirfenidone in adults with iSGS receiving standardized intralesional steroid therapy.

Approximately 40 participants aged 18-65 years with a diagnosis of iSGS will be enrolled across two tertiary airway centres (London Health Sciences Centre - Victoria Hospital and St. Michael's Hospital, University of Toronto). Participants will be randomized in a 1:1 ratio to receive oral pirfenidone or matching placebo for 52 weeks, in addition to protocolized intralesional steroid injections. Pirfenidone will be titrated from 801 mg/day in Week 1 to 1,602 mg/day in Week 2 and 2,403 mg/day (801 mg three times daily) from Week 3 onward, as tolerated. Study drug and placebo will be identical in appearance, and participants, investigators, and study staff will remain blinded to treatment allocation unless unblinding is required for safety.

The primary objective is to assess the safety and tolerability of 52 weeks of pirfenidone treatment in iSGS, measured by the incidence and severity of treatment-emergent adverse events (TEAEs), dose reductions, treatment discontinuations, and protocol-defined laboratory abnormalities, particularly elevations in liver enzymes. Safety monitoring will include regular clinical assessments, vital signs, complete blood counts, renal function, and liver function tests at baseline, early after initiation, and at 3-month intervals. An independent Data Safety Monitoring Board will periodically review blinded safety data and provide recommendations regarding trial continuation or modification.

Secondary and exploratory outcomes will characterize preliminary efficacy signals. These include time from randomization to first endoscopic dilation, total number of dilations during the 52-week treatment period, changes in peak expiratory flow, and patient-reported outcomes assessed using the Dyspnea Index, modified Medical Research Council (mMRC) dyspnea scale, and Voice Handicap Index (VHI). Endoscopic laryngoscopic assessments will document airway patency and subglottic mucosal appearance over time, and may be correlated with clinical and functional outcomes. The study is powered for the primary safety endpoint and will provide effect size estimates for future Phase II/III trials.

Concomitant medications will be managed to minimize interactions with pirfenidone, with exclusion of strong CYP1A2 inhibitors, CYP1A2 inducers such as smoking, and other antifibrotic agents. Participants will receive education on dosing with food, sun protection to reduce photosensitivity risk, adherence strategies, and timely reporting of side effects. Compliance will be assessed via pill counts, medication diaries, and scheduled visits every 3 months, supplemented with interim contact as needed.

This trial is designed to establish the feasibility and safety of systemic antifibrotic therapy in iSGS while generating early evidence on its potential to reduce procedure frequency and improve respiratory and voice-related quality of life. The results will inform the design of subsequent larger, confirmatory studies and may represent a critical step toward introducing the first disease-modifying pharmacologic therapy for this rare airway disorder.