Pulmonary Fibrosis

This chapter is the antifibrotic-pharmacotherapy deep dive of the platform's interstitial lung disease (ILD) content — itself authored primarily from Canadian Thoracic Society position statements.^[1] For the HRCT/multidisciplinary-discussion diagnostic pathway, the full ILD differential (connective-tissue-disease-associated ILD, hypersensitivity pneumonitis, drug-induced ILD, sarcoidosis), and the general framework for oxygen therapy, pulmonary rehabilitation, and palliative care, see the companion Interstitial Lung Disease chapter. This chapter assumes a confirmed diagnosis of idiopathic pulmonary fibrosis (IPF) and goes deep on the single decision that most defines pharmacist involvement in this disease: choosing, initiating, and safely monitoring antifibrotic therapy.

The usual interstitial pneumonia (UIP) pattern — the diagnostic anchor, from two angles

UIP is both a radiographic pattern on high-resolution CT and, when biopsy is performed, a histologic pattern — IPF is fundamentally the clinical diagnosis reached when a UIP pattern is found without an identifiable alternative cause.^[2] The companion ILD chapter details the four HRCT categories (UIP, probable UIP, indeterminate for UIP, alternative diagnosis) that anchor the imaging side of that diagnosis. On the histologic side — relevant only in the minority of patients who proceed to surgical lung biopsy — UIP is defined by patchy, subpleural- and paraseptal-predominant fibrosis with temporal heterogeneity (areas of old, dense scarring and honeycomb change sitting immediately adjacent to relatively normal lung, rather than a single-stage, uniform process), fibroblastic foci (small aggregates of proliferating fibroblasts/myofibroblasts at the leading edge of fibrosis, believed to mark the site of ongoing injury and aberrant repair), and honeycomb change, without granulomas or the marked interstitial inflammation that would suggest an alternative diagnosis.^[2] This histologic pattern is the biological reason antifibrotic therapy specifically targets fibroblast activity (see Choose Initial Treatment) rather than inflammation.

Progressive and largely irreversible

Once fibrosis and honeycomb change have formed, that scar tissue does not resolve with any currently available therapy — this is the biological fact behind the central counseling point in Treatment Targets.^[2] Prognosis is also highly variable between individual patients, which is why this chapter leans on an individualized tool rather than a single population-wide survival figure: the GAP index, a simple four-variable score that assigns a stage (I, II, or III) and a matching 1-, 2-, and 3-year mortality estimate to any patient with IPF, recalculable at any point in the disease course (see Assessment & Diagnosis).^[3]

Antifibrotic therapy — the centerpiece of this chapter

Pirfenidone and nintedanib are the only two agents with a guideline recommendation in favour of use in IPF, and both slow — not reverse — the rate of fibrotic progression.^[2] Choose Initial Treatment in this chapter goes beyond the recommendation itself into the pivotal trial evidence behind it, the specific pharmacokinetic interactions most relevant to community and hospital pharmacists (smoking and pirfenidone; P-glycoprotein/CYP3A4 drugs and nintedanib), and a genuinely important reversal in the guidance around antacid therapy that every pharmacist counseling an IPF patient should know about.

Symptom recognition

The classic presentation (progressive exertional dyspnea and dry cough over months to years, bibasilar "Velcro" crackles, with or without digital clubbing) and the clinical clues that point away from IPF toward an alternative ILD are covered in the companion Interstitial Lung Disease chapter's Recognize the Condition section and are not repeated here.

Three recognized patterns of disease progression

Not every patient with IPF declines the same way, and recognizing which pattern is unfolding changes the urgency of the response:

• Slow, gradual decline — the most common pattern, with a measurable but incremental loss of FVC over years; this is the population the pivotal antifibrotic trials primarily enrolled, and the pattern antifibrotic therapy is best studied for slowing.^[2]
• Rapid progressors — a meaningful minority of patients decline substantially faster from diagnosis, with a steeper FVC trajectory and shorter survival despite the same nominal diagnosis; this subgroup is part of the rationale for individualized, GAP-index-based prognostication rather than a single population-average timeline (see Assessment & Diagnosis).^[3]
• Stepwise decline punctuated by acute exacerbations — periods of relative stability interrupted by acute, severe deteriorations (see Special Populations and the companion ILD chapter's coverage of acute exacerbation of IPF), each of which can leave a permanent downward step in baseline function even in a survivor.^[2]

The "categorical decline" a pharmacist should recognize as clinically significant

A relative decline in FVC % predicted of 10% or more, or a smaller absolute FVC decline combined with worsening symptoms or radiographic progression, over a 6- to 12-month interval is the threshold used in the literature to define clinically meaningful progression — this is the number that should prompt a treatment reassessment (see Red Flags & Refer and Treatment Failure/Next Step) rather than a vaguer sense that "the patient seems more short of breath."^[2]

Occupational and environmental exposures

Beyond the genetic and demographic risk factors detailed in the companion ILD chapter (older age, male sex, smoking history, the MUC5B promoter polymorphism, and telomere-related gene variants in familial disease), a systematic review and meta-analysis of occupational exposures found significantly increased IPF risk with metal dust (pooled odds ratio 1.83) and wood dust (pooled odds ratio 1.62) exposure, alongside earlier case-control data implicating farming, livestock, and stone/sand exposure.^[4] An occupational history — trade, hobbies, and duration of exposure — is worth asking about specifically at a new IPF diagnosis, independent of the hypersensitivity-pneumonitis-specific exposure history covered in the companion chapter.

Gastroesophageal reflux and occult microaspiration — a disputed risk factor

Gastroesophageal reflux disease (GERD) and occult microaspiration have long been proposed as a possible contributor to IPF development and a driver of ongoing lung injury, based on the high prevalence of abnormal esophageal acid exposure found in IPF cohorts.^[2] This hypothesis is exactly why antacid therapy was, for a time, considered a reasonable IPF-directed adjunct — and exactly why its reversal in the current guideline is such an important, counterintuitive teaching point (see Choose Initial Treatment).

Comorbidities that compound risk and prognosis

Obesity, type 2 diabetes mellitus, and obstructive sleep apnea are all more prevalent in IPF than in the general population and are increasingly recognized as risk-amplifying comorbidities rather than incidental findings — screen for and manage them as part of comprehensive IPF care, alongside the cardiopulmonary comorbidity screening detailed in the companion chapter's Monitoring & Follow-Up.

Diagnosis itself

The HRCT/pulmonary-function/multidisciplinary-discussion pathway that establishes an IPF diagnosis is covered fully in the companion Interstitial Lung Disease chapter's Assessment & Diagnosis section. This section instead covers the two things a pharmacist and the broader care team need once that diagnosis is already established: staging prognosis, and confirming antifibrotic candidacy.

The GAP index — individualized staging and prognosis

The GAP index is a simple four-variable point score — Gender, Age, and two Physiology variables (FVC % predicted and DLCO % predicted) — derived and validated in 558 patients with IPF and designed to be recalculated at any point in the disease course, not only at diagnosis.^[3]

Total points map to three stages, each with its own 1-, 2-, and 3-year mortality: Stage I (0-3 points) — 1-year mortality 5.6%, 2-year 10.9%, 3-year 16.3%; Stage II (4-5 points) — 1-year 16.2%, 2-year 29.9%, 3-year 42.1%; Stage III (6-8 points) — 1-year 39.2%, 2-year 62.1%, 3-year 76.8%.^[3] Recalculating the GAP stage at routine follow-up (see Monitoring & Follow-Up) turns an abstract sense of "getting worse" into a concrete, reproducible number that can guide the urgency of a transplant-referral conversation (see Special Populations and the companion ILD chapter).

Confirming antifibrotic candidacy — the pre-treatment workup

Once IPF is confirmed and before pirfenidone or nintedanib is started, confirm the following, which map directly onto each agent's specific risk profile in Choose Initial Treatment:

• Baseline liver enzymes and bilirubin for both agents.
• Smoking status, specifically for a pirfenidone candidate — active smoking substantially lowers pirfenidone exposure through CYP1A2 induction (see Choose Initial Treatment), which matters both for counseling and for interpreting an apparent lack of effect.
• Sun-sensitivity and skin-cancer history, specifically for a pirfenidone candidate, to individualize the intensity of sun-protection counseling.
• Pregnancy test (in anyone of reproductive potential) and a GI bleeding/perforation and anticoagulant-use history, specifically for a nintedanib candidate.
• A full medication reconciliation for interacting drugs — strong CYP1A2 inhibitors/inducers for pirfenidone; P-glycoprotein/CYP3A4 inhibitors and inducers for nintedanib (see Choose Initial Treatment for the specific drug lists).

The single most important thing to communicate before the first dose of any antifibrotic is prescribed: pirfenidone and nintedanib slow the rate of FVC decline — they do not stop it, and they do not reverse fibrosis that has already formed. This is not a vague caveat; it is exactly what the pivotal trials showed, in patients on active treatment as much as in those on placebo.

• In the ASCEND trial, patients on pirfenidone still lost a mean of 235 mL of FVC over 52 weeks — meaningfully less than the 428 mL lost on placebo (p<0.001), a roughly 45% relative reduction in the rate of decline, but a decline nonetheless.^[5]
• Across the two INPULSIS trials, nintedanib reduced the adjusted annual rate of FVC decline by close to half compared with placebo (-114.7 vs. -239.9 mL/year in INPULSIS-1; -113.6 vs. -207.3 mL/year in INPULSIS-2) — again, a slower decline, not a plateau or an improvement.^[6]

Set this expectation explicitly, before therapy starts: a useful framing for patients is that antifibrotic therapy is meant to flatten the slope of decline, not turn back the clock. A patient who starts therapy expecting their breathlessness to improve is set up for a painful, avoidable disappointment a few months in — and may stop a genuinely beneficial therapy for the wrong reason (see Common Errors to Avoid).

• Slow the rate of fibrotic progression — the primary, evidence-based target of antifibrotic therapy (see Choose Initial Treatment).
• Delay crossing into a higher GAP stage — reframing "slower decline" as a concrete, individualized target tied to the staging tool in Assessment & Diagnosis, rather than an abstract population-level statistic.
• Preserve tolerability, not just efficacy — a therapy the patient cannot tolerate provides no benefit; the adverse-effect management detailed in Choose Initial Treatment is not a secondary concern.
• Manage symptoms and preserve quality of life alongside disease-modifying therapy, using the pulmonary rehabilitation, oxygen, and symptom-management approach detailed in the companion ILD chapter, plus the nutrition-focused counseling in Non-Pharmacologic Treatment specific to antifibrotic-associated weight loss.

Pulmonary rehabilitation, oxygen, cough/dyspnea management, and palliative care

The evidence and initiation criteria for pulmonary rehabilitation, supplemental oxygen (continuous and ambulatory), non-pharmacologic cough/dyspnea strategies, vaccination, smoking cessation, and advance-care-planning timing are covered fully in the companion Interstitial Lung Disease chapter's Non-Pharmacologic Treatment section and apply equally to IPF; they are not repeated here.

Nutrition and weight management — an antifibrotic-specific addition

Weight loss is a genuinely common adverse effect of both antifibrotic agents — reported in a meaningful proportion of patients in the pivotal trials — and it compounds any disease-related loss of appetite or increased work of breathing.^[8][9] Proactive counseling from the point of treatment initiation, not only once weight loss is already significant, includes:

• Small, frequent, calorie-dense meals rather than three large meals, particularly useful for a patient with pirfenidone-associated early satiety or GI upset.
• Oral nutritional supplementation for a patient with ongoing unintentional weight loss.
• A dietitian referral threshold of roughly 5% unintentional body-weight loss over a month, or any weight loss that is symptomatic or accelerating — do not wait for a formal malnutrition diagnosis before referring.
• Distinguishing antifibrotic-associated weight loss from disease-related cachexia at each visit, since the management approach differs (dose/tolerability review for the former, broader supportive care for the latter).

Clinical trial referral for progressive disease

A patient with confirmed categorical decline (see Recognize the Condition) despite adherent, well-tolerated antifibrotic therapy is a reasonable candidate for referral to an ILD-specialist centre to discuss clinical trial enrollment in investigational agents, alongside the transplant-referral conversation covered in Special Populations and the companion ILD chapter.

Perioperative and pre-transplant antifibrotic management

Both agents carry a theoretical concern about impaired wound and anastomotic healing, and European regulatory guidance advises discontinuing nintedanib before major surgery given its antiangiogenic mechanism, though without a specified interval.^[13] In practice, the short half-lives of both drugs (nintedanib roughly 10-15 hours; pirfenidone under an hour) limit how long any residual effect could plausibly persist, and neither is continued after transplantation itself.^[13]

Real-world outcome data in patients continuing antifibrotic therapy up to lung transplantation are reassuring rather than alarming: a multicentre French cohort found similar rates of perioperative bleeding, wound and bronchial anastomotic complications, and 30-day/1-year survival between patients on and off antifibrotic therapy at the time of transplant, with better-preserved pre-transplant lung function in those who continued treatment.^[13] The practical takeaway: do not reflexively stop an antifibrotic before a minor procedure on a generic "just in case" basis — this is an individualized, specialist-directed decision, not an automatic hold (see Common Errors to Avoid).

Polypharmacy and the elderly

IPF is predominantly a disease of older adults, who are disproportionately likely to be on P-glycoprotein/CYP3A4-interacting medications for unrelated indications (certain calcium channel blockers, amiodarone, some statins, azole antifungals). Because nintedanib's interaction profile is genuinely different from pirfenidone's CYP1A2-centred one (see Choose Initial Treatment), a full medication reconciliation specifically for P-gp/CYP3A4 interactions is worth repeating whenever a new medication is added — not only at antifibrotic initiation.

Hepatic/renal impairment, pregnancy, and lactation

These are covered in full in the companion Interstitial Lung Disease chapter's Special Populations section and apply identically here — both agents' hepatic-impairment dose adjustments, pirfenidone's severe-renal-impairment contraindication, and nintedanib's pregnancy contraindication and breastfeeding cautions are not duplicated in this chapter.

• Liver-function monitoring on the product-specific schedule — pirfenidone: ALT/AST/bilirubin at baseline, monthly for 6 months, then every 3 months; nintedanib: baseline, monthly for 3 months, then periodically (e.g., each visit) thereafter (full dose-modification thresholds in Choose Initial Treatment and Drug Tables).^[8][9]
• Recalculate the GAP index at routine follow-up (see Assessment & Diagnosis) whenever updated FVC and DLCO are available — a stage change is a concrete, reproducible way to flag that the transplant-referral conversation (see Special Populations) needs to be revisited.^[3]
• Reassess smoking status specifically in a patient on pirfenidone at every visit — a change in smoking status meaningfully changes pirfenidone exposure through CYP1A2 induction (see Choose Initial Treatment).
• Re-screen the medication list for new CYP1A2 (pirfenidone) or P-glycoprotein/CYP3A4 (nintedanib) interacting drugs at every visit and whenever a new prescription is added, not only at antifibrotic initiation.
• Monitor weight and nutritional status given the antifibrotic-associated weight loss discussed in Non-Pharmacologic Treatment; use the roughly 5% unintentional weight-loss threshold to trigger dietitian referral.
• Pulmonary function testing (FVC/DLCO) frequency, 6-minute walk testing, follow-up imaging, and comorbidity/vaccination screening follow the schedule detailed in the companion ILD chapter's Monitoring & Follow-Up section and are not duplicated here.

1. Confirm true intolerance before assuming treatment failure. Distinguish a genuinely intolerable adverse effect (severe photosensitivity, persistent severe diarrhea, a significant liver enzyme elevation) from a milder, manageable one that reinforced counseling and dose adjustment can resolve (see Choose Initial Treatment) — do not discontinue a disease-modifying therapy for a mild, expected, manageable effect.
2. For confirmed intolerance of one antifibrotic, consider switching to the other rather than stopping antifibrotic therapy altogether. This is not yet a formal guideline recommendation, but a growing body of real-world evidence supports it: in one series, patients who discontinued pirfenidone for adverse effects (diarrhea, nausea, photosensitivity, or difficulty with the three-times-daily schedule) were subsequently able to tolerate nintedanib, and separate real-world data support switching from nintedanib to pirfenidone for intolerance as well.^[14] This applies specifically to confirmed intolerance — not to a perceived lack of efficacy, where switching has no evidence base (see below).
3. For continued categorical decline (see Recognize the Condition) despite confirmed adherence and tolerability on either agent, there is no evidence to support switching to the other agent, and no established added efficacy benefit to combining both (see Choose Initial Treatment's INJOURNEY discussion). Instead: recalculate the GAP index, exclude an unrecognized second process or an unrecognized acute exacerbation, escalate the urgency of the transplant-referral conversation (see Special Populations), and consider specialist referral for clinical trial enrollment (see Non-Pharmacologic Treatment).
4. Pirfenidone-associated photosensitivity or GI intolerance: reinforce sun-protection and food-administration counseling first; use dose reduction or temporary interruption per the monograph, with re-escalation through the titration schedule once resolved.^[8]
5. Nintedanib-associated diarrhea: start hydration and an anti-diarrheal (e.g., loperamide) at first sign; escalate to dose reduction (100 mg twice daily) or temporary interruption for a persistent or more severe episode.^[9]
6. Liver enzyme elevation on either agent: apply the agent-specific threshold precisely (see Choose Initial Treatment) — do not default to permanent discontinuation for a mild, asymptomatic elevation, but do not rechallenge after a marked elevation or one accompanied by symptoms of liver injury.^[8][9]
7. A patient who continues smoking despite counseling on pirfenidone: reinforce cessation counseling specifically framed around drug exposure (see Choose Initial Treatment), and do not interpret a plateau in benefit as drug failure without first addressing this modifiable factor.

• Starting or continuing a PPI or H2-receptor antagonist specifically "for the lungs" in an IPF patient — the current guideline gives a conditional recommendation against antacid therapy for this purpose (see Choose Initial Treatment); treat genuine reflux symptoms on their own merits only.
• Not asking about a change in smoking status in a patient on pirfenidone — starting or stopping smoking mid-therapy meaningfully changes drug exposure through CYP1A2 induction, in either direction.
• Co-prescribing a strong P-glycoprotein/CYP3A4 inducer (rifampicin, carbamazepine, phenytoin, St. John's wort) with nintedanib without recognizing that this can silently reduce efficacy, or a strong inhibitor (ketoconazole, erythromycin, clarithromycin, cyclosporine) without the closer tolerability monitoring it requires.
• Assuming that combining pirfenidone and nintedanib is simply "more aggressive treatment" and therefore better — INJOURNEY data show more GI adverse effects without a proven added efficacy benefit; this is not a default escalation strategy.
• Reflexively discontinuing an antifibrotic before a minor or elective procedure — real-world perioperative and pre-transplant data have not shown a clear complication signal; this should be an individualized, specialist-directed decision (see Special Populations).
• Interpreting a single, modest FVC fluctuation as drug failure and abandoning a well-tolerated antifibrotic — use the actual categorical-decline threshold (a relative FVC decline of 10% or more over 6-12 months) rather than a vague impression (see Recognize the Condition).
• Telling a patient that antifibrotic therapy will improve or stabilize their lung function outright — even in the pivotal trials, patients on active treatment still lost lung function, just more slowly than on placebo (see Treatment Targets); set this expectation explicitly before the first dose.
• Discontinuing an antifibrotic permanently after a single mild, asymptomatic liver enzyme elevation instead of following the agent-specific dose-interruption-and-rechallenge pathway.^[8][9]
• Forgetting that a gap of more than 14 consecutive days of missed pirfenidone doses requires restarting the full 14-day titration, not resuming at the maintenance dose.
• Prescribing the combination of prednisone, azathioprine, and N-acetylcysteine for IPF specifically — PANTHER-IPF showed this combination causes harm (increased mortality and hospitalization), not merely a lack of benefit (see Choose Initial Treatment).^[10]

Antifibrotic Agents — Full Dosing, Monitoring, and Interaction Detail

The two guideline-endorsed, disease-modifying agents for IPF. No guideline preference exists between them — individualize by adverse-effect and interaction profile. See Choose Initial Treatment for the pivotal trial evidence and the counseling points behind each interaction.

Not Recommended as IPF-Directed Therapy

These are discussed in Choose Initial Treatment for their teaching value, not offered here as prescribable IPF options: the combination of prednisone, azathioprine, and N-acetylcysteine (PANTHER-IPF showed harm, not just a lack of benefit); antacid therapy — a proton pump inhibitor or H2-receptor antagonist — used specifically to improve respiratory outcomes (no benefit shown, and a possible increased pulmonary infection risk in advanced disease, per the current guideline's conditional recommendation against); and routine combination of pirfenidone with nintedanib (tolerable over a 12-week trial, but not proven more effective than either agent alone).