Pulmonary Fibrosis

Clinical Snapshot

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.

Recognize the Condition

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]

Risk Factors

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.

Red Flags & Refer

These findings in a patient on antifibrotic therapy warrant same-day pharmacist action — a call to the prescriber or an urgent referral — rather than being noted for the next routine visit:

Severe or blistering photosensitivity/skin reaction on pirfenidone — hold the dose and arrange prompt reassessment; this is distinct from the milder, expected rash/photosensitivity that sun-protection counseling is meant to prevent (see Choose Initial Treatment).
Severe abdominal pain, rigidity, fever, or GI bleeding (hematemesis, melena, hematochezia) on nintedanib — evaluate urgently for gastrointestinal perforation or a bleeding event; nintedanib's antiangiogenic mechanism carries a small but real risk of both.
New or worsening bruising, epistaxis, or bleeding in a patient on nintedanib who is also anticoagulated — reassess the interaction and bleeding risk rather than assuming it is unrelated to the antifibrotic.
Jaundice, dark urine, right-upper-quadrant pain, or unexplained fatigue/anorexia on either agent — obtain urgent liver enzymes and hold the drug per the agent-specific threshold rather than waiting for the next scheduled LFT draw (see Choose Initial Treatment).
A relative FVC decline of 10% or more over 6-12 months despite adherence — this categorical decline (see Recognize the Condition) should trigger prompt reassessment of the treatment plan and transplant-referral urgency, not simply a note for the next routine visit (see Treatment Failure/Next Step and the companion ILD chapter's transplant-referral criteria).
A gap of more than 14 consecutive days of missed pirfenidone doses — the full 14-day titration must restart from the beginning; resuming at the maintenance dose risks significant, avoidable adverse effects (see Choose Initial Treatment).

Acute worsening of dyspnea or hypoxemia is addressed separately, in the companion ILD chapter's acute-exacerbation-of-IPF pathway, which is not duplicated here.

Assessment & Diagnosis

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]

Variable	Points
Sex: female	0
Sex: male	1
Age ≤ 60 years	0
Age 61-65 years	1
Age > 65 years	2
FVC > 75% predicted	0
FVC 50-75% predicted	1
FVC < 50% predicted	2
DLCO > 55% predicted	0
DLCO 36-55% predicted	1
DLCO ≤ 35% predicted	2
DLCO cannot be performed (e.g., due to severity)	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).

Treatment Targets

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.

Choose Initial Treatment

The evidence behind "start an antifibrotic" — what the pivotal trials actually showed

Pirfenidone: the two CAPACITY trials gave mixed results — CAPACITY 004 met its primary endpoint (FVC % predicted decline of -8.0% vs. -12.4% with placebo over 72 weeks, p=0.001), while CAPACITY 006 did not, which is why regulators required a confirmatory trial before approval.^[7] That trial, ASCEND, was unambiguous: at 52 weeks, mean FVC decline was 235 mL with pirfenidone versus 428 mL with placebo (p<0.001), and pirfenidone produced a 47.9% relative reduction in the proportion of patients who either died or had an absolute FVC decline of 10% or more.^[5]

Nintedanib: the two INPULSIS trials were consistent with each other from the start — nintedanib reduced the adjusted annual rate of FVC decline by close to 50% in both (INPULSIS-1: -114.7 vs. -239.9 mL/year; INPULSIS-2: -113.6 vs. -207.3 mL/year), with diarrhea as the dominant tolerability issue in both (roughly 62% vs. 19% on placebo).^[6]

Neither trial programme demonstrated stabilization or reversal — patients on active treatment still lost lung function, just at roughly half the rate of those on placebo. This is the evidence base behind the counseling point in Treatment Targets, and it is worth having the actual numbers on hand for a skeptical or discouraged patient.

Pirfenidone — dosing and the smoking/CYP1A2 interaction a pharmacist should specifically flag

Dosing: titrate over 14 days to a maintenance dose of 801 mg PO three times daily with food; if more than 14 consecutive days of doses are missed, restart the full 14-day titration rather than resuming at maintenance (full schedule and required liver-function monitoring calendar in Drug Tables).

Smoking substantially lowers pirfenidone exposure: pirfenidone is metabolized primarily via CYP1A2, and tobacco smoke — a CYP1A2 inducer — reduces pirfenidone exposure (AUC) by roughly 50% in smokers compared with non-smokers.^[8] This has two practical implications a pharmacist is well positioned to catch: first, counsel every patient to stop smoking before and during pirfenidone therapy, framed not only as general health advice but as something that directly affects whether the drug reaches an effective exposure; second, if a patient who was smoking at treatment initiation later quits, their pirfenidone exposure will rise — this is a reasonable moment to reinforce tolerability counseling (photosensitivity, GI effects) rather than assuming the regimen is unchanged.

Fluvoxamine remains a true contraindication (a strong CYP1A2 inhibitor — an average nearly 6-fold increase in pirfenidone exposure with concurrent use in a dedicated interaction study), and dose reduction is required with ciprofloxacin 750 mg twice daily or another strong CYP1A2 inhibitor.^[8]

Nintedanib — dosing and the P-glycoprotein/CYP3A4 interactions a pharmacist should specifically flag

Dosing: 150 mg PO twice daily, approximately 12 hours apart, with food, capsule swallowed whole (full schedule and required liver-function monitoring calendar in Drug Tables).

Nintedanib is a P-glycoprotein (P-gp) substrate and, to a lesser extent, a CYP3A4 substrate — a genuinely different interaction profile from pirfenidone's CYP1A2-centred one, and worth screening for separately at every medication reconciliation:

Strong P-gp/CYP3A4 inhibitors (e.g., ketoconazole, itraconazole, erythromycin, clarithromycin, cyclosporine) increase nintedanib exposure — a dedicated interaction study found a 1.61-fold increase in AUC and a 1.83-fold increase in Cmax with ketoconazole.^[9] Monitor closely for tolerability (diarrhea, LFT elevation) with concomitant use, and manage with dose interruption, reduction to 100 mg twice daily, or discontinuation as needed.
Strong P-gp/CYP3A4 inducers (e.g., rifampicin, carbamazepine, phenytoin, St. John's wort) reduce nintedanib exposure substantially — rifampicin decreased nintedanib AUC to about 50% and Cmax to about 60% of baseline in a dedicated interaction study — and should be avoided, since this can silently undercut the drug's efficacy without producing an obvious adverse effect to prompt a dose reassessment.^[9]
Anticoagulants — nintedanib's antiangiogenic mechanism carries an increased bleeding risk; full-dose anticoagulation is not an automatic contraindication, but it does warrant closer monitoring and a specific discussion of the added risk.

PANTHER-IPF — the landmark trial behind the strongest "do not" in this chapter

Before antifibrotic therapy existed, combination immunosuppression — prednisone, azathioprine, and N-acetylcysteine together — was commonly used for IPF on the reasonable-sounding theory that inflammation drives fibrosis. The PANTHER-IPF trial tested this directly: patients with mild-to-moderate IPF were randomized to combination therapy, N-acetylcysteine alone, or placebo.^[10]

At a planned interim analysis with about half the target enrollment collected, the data and safety monitoring board stopped the combination-therapy arm early: patients on prednisone/azathioprine/NAC had significantly higher all-cause mortality and more hospitalizations than those on placebo, with no offsetting benefit on FVC decline.^[10] This is a genuinely counterintuitive result worth stating plainly to a learner or a patient who assumes "more aggressive treatment" is always better: a plausible-sounding, previously common therapy was shown to cause harm in a randomized trial, not merely to lack benefit.

The practical rule that follows directly from PANTHER-IPF: do not initiate the combination of prednisone, azathioprine, and N-acetylcysteine to treat IPF — a strong recommendation against, carried forward unchanged into the current guideline.^[2] This is specific to IPF; the same combination, or other immunosuppression, remains appropriate for other fibrotic ILDs such as connective-tissue-disease-associated ILD, where the underlying biology is genuinely different (see the companion ILD chapter's Special Populations).

Antacid therapy for IPF — a real guidance reversal worth knowing about

Gastroesophageal reflux and occult microaspiration were long hypothesized as a driver of ongoing lung injury in IPF (see Risk Factors), and earlier guidance had left the door open to antacid therapy — a proton pump inhibitor (PPI) or H2-receptor antagonist — as a reasonable adjunct specifically for its effect on the lungs, not just for reflux symptoms.

That position has since reversed. A pooled post-hoc analysis of the placebo arms of the CAPACITY and ASCEND pirfenidone trials found no improvement in disease outcomes with antacid therapy, and a signal of more pulmonary infections among antacid users with more advanced disease.^[11] The current international guideline now gives a conditional recommendation against using antacid medication, and a separate conditional recommendation against referring for antireflux surgery, specifically to improve respiratory outcomes in IPF.^[2]

The practical rule: do not start or continue a PPI or H2-receptor antagonist "for the lungs" in an IPF patient. If a patient has genuine reflux symptoms, treat those on their own independent merits — but stop framing antacid therapy as IPF-directed treatment, and do not use it as a substitute for, or an addition to, antifibrotic therapy.

Combining pirfenidone and nintedanib — tolerable in trials, but not a proven strategy

The INJOURNEY trial specifically tested adding pirfenidone on top of existing nintedanib therapy over 12 weeks. The combination produced no new safety signal and no clinically relevant pharmacokinetic interaction between the two drugs, but it did produce more gastrointestinal adverse effects (diarrhea, nausea, vomiting) than nintedanib alone, without an established added efficacy benefit over either drug given alone.^[12]

The practical rule: combination antifibrotic therapy is not a routine escalation strategy for an inadequate response to a single agent — it has been shown to be tolerable over a short trial period, not proven more effective, and should only be considered on an individualized, specialist-directed basis (see Treatment Failure/Next Step).

Non-Pharmacologic Treatment

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.

Pharmacologic Treatment Options

Drug / intervention	Role	Dose / use	Important adverse effects	Teaching points
Pirfenidone Guideline-endorsed antifibrotic	Slows FVC decline in IPF (ASCEND trial evidence)	Titrate over 14 days to 801 mg PO three times daily with food (full schedule in Drug Tables)	Photosensitivity/rash, GI upset, elevated LFTs, weight loss	Exposure drops ~50% with active smoking (CYP1A2 induction) — reassess tolerability if the patient quits smoking mid-therapy; daily SPF 50+ sun protection from day one
Nintedanib Guideline-endorsed antifibrotic	Slows FVC decline in IPF (INPULSIS trial evidence)	150 mg PO twice daily with food, capsule swallowed whole (full schedule in Drug Tables)	Diarrhea, GI perforation/bleeding risk, elevated LFTs, weight loss	Screen for P-glycoprotein/CYP3A4 inhibitors and inducers at every visit — the interaction risk profile is genuinely different from pirfenidone's
Combination pirfenidone + nintedanib Not a routine strategy	Investigated in the 12-week INJOURNEY trial as add-on therapy — tolerable, but no proven added efficacy over either agent alone	Individualized, specialist-directed only	More GI adverse effects (diarrhea, nausea, vomiting) than either agent alone, no clinically relevant PK interaction between the two drugs	Do not initiate as a default escalation for perceived treatment failure
Antacid therapy (PPI or H2-receptor antagonist) Not recommended as IPF-directed therapy	Historically proposed for reflux/microaspiration-driven lung injury; the current guideline gives a conditional recommendation against use for this purpose	N/A for IPF — treat only independent, symptomatic reflux, not as IPF-directed therapy	A pooled analysis found no disease-outcome benefit and a signal of more pulmonary infection in advanced disease	Antireflux surgery for the same purpose is also not recommended

Special Populations

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.

Monitoring & Follow-Up

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.

Treatment Failure / Next Step

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.
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).
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).
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]
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]
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]
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.

Common Errors to Avoid

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]

Clinical Decision Algorithm

Algorithm A — From confirmed IPF to antifibrotic initiation

IPF confirmed by multidisciplinary discussion (see companion ILD chapter for the full diagnostic pathway)

Calculate the GAP index to stage baseline severity and set follow-up intensity^[3]

Baseline workup: LFTs (both agents); smoking status and sun-sensitivity history (pirfenidone); pregnancy test and GI bleeding/anticoagulant history (nintedanib); medication reconciliation for CYP1A2/P-gp/CYP3A4 interactions

Pirfenidone selected

Titrate over 14 days to 801 mg PO TID with food

LFTs monthly x6 months, then every 3 months; daily sun protection; reassess exposure if smoking status changes^[8]

Nintedanib selected

Start 150 mg PO BID with food

LFTs monthly x3 months, then periodically; screen for P-gp/CYP3A4 interactions at every visit^[9]

Neither tolerated after dose adjustment

Do not add a PPI/H2RA or combine both agents as a default escalation — see Algorithm B for confirmed intolerance

Set expectations explicitly: slows decline, does not reverse fibrosis. Continue routine monitoring (see Monitoring & Follow-Up)

Algorithm B — Suspected antifibrotic intolerance or categorical decline

New adverse effect, or a relative FVC decline of 10% or more over 6-12 months, on pirfenidone or nintedanib

Adverse effect — mild/moderate and manageable

Reinforce supportive counseling (sun protection, or loperamide plus hydration) and use product-specific dose reduction; re-escalate once resolved

Adverse effect — severe, or persistent despite dose adjustment

Discontinue the current agent per product-specific criteria

Consider switching to the alternate antifibrotic for confirmed intolerance — real-world data support reasonable tolerability after a switch^[14]

Categorical decline despite confirmed adherence and tolerability: recalculate GAP stage, exclude an unrecognized second process, escalate transplant-referral urgency^[3]

No evidence supports switching agents, or combining both, for perceived lack of efficacy alone — this is a specialist-directed decision, not a default escalation

Drug Tables

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.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Pirfenidone	Titrate over 14 days: 267 mg PO TID (days 1-7) -> 534 mg PO TID (days 8-14) -> 801 mg PO TID maintenance (day 15+), always with food. Restart the full 14-day titration if more than 14 consecutive days of doses are missed.	Photosensitivity/rash, nausea, abdominal pain, diarrhea, dyspepsia, fatigue, headache, dizziness, elevated LFTs, weight loss	Contraindicated with fluvoxamine (strong CYP1A2 inhibitor, ~6-fold increase in exposure); dose reduction required with ciprofloxacin 750 mg BID or another strong CYP1A2 inhibitor; active smoking (CYP1A2 induction) lowers exposure by roughly 50%	LFTs (ALT/AST/bilirubin) at baseline, monthly x6 months, then every 3 months. Daily SPF 50+ sunscreen and sun avoidance from the first dose. Reassess tolerability if smoking status changes mid-therapy.
Nintedanib	150 mg PO twice daily, approximately 12 hours apart, with food; swallow capsule whole. Missed dose: resume at the next scheduled time, do not exceed 300 mg/day.	Diarrhea (dominant AE, usually within 3 months), GI perforation and bleeding risk, elevated LFTs, weight loss, hypertension	P-glycoprotein/CYP3A4 substrate — strong inhibitors (ketoconazole, itraconazole, erythromycin, clarithromycin, cyclosporine) increase exposure (ketoconazole: 1.61-fold AUC increase); strong inducers (rifampicin, carbamazepine, phenytoin, St. John's wort) reduce exposure (rifampicin: AUC reduced to ~50%) and should be avoided; increased bleeding risk with full-dose anticoagulation	LFTs at baseline, monthly x3 months, then periodically thereafter. Contraindicated in pregnancy and in peanut/soya hypersensitivity (capsule shell contains soya lecithin). Short half-life (~10-15 hours); theoretical but not clearly demonstrated perioperative bleeding/healing risk.

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).

References

Comprehensive management of fibrotic interstitial lung diseases: A Canadian Thoracic Society position statement — Canadian Thoracic Society ILD Clinical Assembly (Assayag D, Camp PG, Fisher J, Johannson KA, Kolb M, et al.). Can J Respir Crit Care Sleep Med 2018;2(4):234-243
Idiopathic Pulmonary Fibrosis (an Update) and Progressive Pulmonary Fibrosis in Adults: An Official ATS/ERS/JRS/ALAT Clinical Practice Guideline — American Thoracic Society/European Respiratory Society/Japanese Respiratory Society/Asociación Latinoamericana de Tórax (Raghu G, Remy-Jardin M, Richeldi L, et al.). Am J Respir Crit Care Med 2022;205(9):e18-e47
A Multidimensional Index and Staging System for Idiopathic Pulmonary Fibrosis — Annals of Internal Medicine (Ley B, Ryerson CJ, Vittinghoff E, et al.). Ann Intern Med 2012;156(10):684-691
Occupational and environmental risk factors of idiopathic pulmonary fibrosis: a systematic review and meta-analyses — Scientific Reports (Park Y, Ahn C, Kim T-H). Sci Rep 2021;11:4318
A Phase 3 Trial of Pirfenidone in Patients with Idiopathic Pulmonary Fibrosis — ASCEND Study Group (King TE Jr, Bradford WZ, Castro-Bernardini S, et al.). N Engl J Med 2014;370(22):2083-2092
Efficacy and Safety of Nintedanib in Idiopathic Pulmonary Fibrosis — INPULSIS Trial Investigators (Richeldi L, du Bois RM, Raghu G, et al.). N Engl J Med 2014;370(22):2071-2082
Pirfenidone in patients with idiopathic pulmonary fibrosis (CAPACITY): two randomised trials — The Lancet (Noble PW, Albera C, Bradford WZ, et al.). Lancet 2011;377(9779):1760-1769
ESBRIET (pirfenidone) Product Monograph — Hoffmann-La Roche Limited. Health Canada Drug Product Database, date of revision August 9, 2018
OFEV (nintedanib) Product Monograph — Boehringer Ingelheim (Canada) Ltd.. Health Canada Drug Product Database, date of revision September 20, 2024
Prednisone, Azathioprine, and N-Acetylcysteine for Pulmonary Fibrosis — Idiopathic Pulmonary Fibrosis Clinical Research Network (Raghu G, Anstrom KJ, King TE Jr, Lasky JA, Martinez FJ). N Engl J Med 2012;366(21):1968-1977
Antacid therapy and disease outcomes in idiopathic pulmonary fibrosis: a pooled analysis — The Lancet Respiratory Medicine (Kreuter M, Wuyts W, Renzoni E, et al.). Lancet Respir Med 2016;4(5):381-389
Nintedanib with Add-on Pirfenidone in Idiopathic Pulmonary Fibrosis. Results of the INJOURNEY Trial — American Thoracic Society (Vancheri C, Kreuter M, Richeldi L, et al.). Am J Respir Crit Care Med 2018;197(3):356-363
Effect of antifibrotic agents on postoperative complications after lung transplantation for idiopathic pulmonary fibrosis — Respirology (Moncomble E, Weisenburger G, Picard C, et al.). Respirology 2024;29(1):71-79
Tolerability and efficacy of switching anti-fibrotic treatment from nintedanib to pirfenidone for idiopathic pulmonary fibrosis — PLOS ONE (Sugino K, Ono H, Saito M, Ando M, Tsuboi E). PLoS One 2024;19(6):e0305429
An Official ATS/ERS/JRS/ALAT Clinical Practice Guideline: Treatment of Idiopathic Pulmonary Fibrosis. An Update of the 2011 Clinical Practice Guideline — American Thoracic Society/European Respiratory Society/Japanese Respiratory Society/Asociación Latinoamericana de Tórax (Raghu G, Rochwerg B, Zhang Y, et al.). Am J Respir Crit Care Med 2015;192(2):e3-e19

Professional reference only. Apply clinical judgment and verify patient-specific decisions against current authoritative guidance and product information.