Next year will be the 80th anniversary of the first description of idiopathic pulmonary fibrosis (IPF). It will also mark 40 years since I graduated from medical school. I spent most of those 40 years specializing in the management of patients with IPF and there have been enormous strides forward in those 40 years. This post will look back on where we have been, where we are now, and where we are going with respect to treating IPF.
First, some definitions.
Interstitial lung diseases are characterized by the accumulation of inflammation or scar or both in the lungs. There are at least 140 different interstitial lung diseases. Pulmonary fibrosis means accumulation of scar in the lungs and many of the interstitial lung diseases can result in pulmonary fibrosis. For most of these, the cause is known, such as rheumatoid arthritis-associated pulmonary fibrosis, radiation-induced pulmonary fibrosis, and asbestosis. Idiopathic pulmonary fibrosis (IPF) is when pulmonary fibrosis occurs without any known underlying cause (“idiopathic” means no obvious cause).
Usual interstitial pneumonitis (UIP) is a pattern of findings on either a chest CT scan or a lung biopsy that is typically seen in idiopathic pulmonary fibrosis. However, the UIP pattern can also be seen in other interstitial lung diseases. For this reason, the radiologist and the pathologist generally do not diagnose idiopathic pulmonary fibrosis – it is up to the pulmonologist who is seeing the patient to diagnose idiopathic pulmonary fibrosis by taking the radiologist’s or pathologist’s finding of UIP in the context of the patient’s history, physical exam, and laboratory test results.
The historical timeline of IPF
There is no one person who discovered idiopathic pulmonary fibrosis. Instead, there has been an evolution of thought about IPF over the past century. Some of the more important points in the timeline of IPF are:
- 1944. The first clinical description of idiopathic pulmonary fibrosis is credited to Drs. Hamman and Rich from Johns Hopkins in 1944 in their description of 4 patients with interstitial lung disease of uncertain cause. Although the term “Hamman-Rich syndrome” became used as a catch-all term for many interstitial lung diseases (including idiopathic pulmonary fibrosis), their 4 patients likely had acute interstitial pneumonitis, which is a different disease.
- 1962. Dr. Gross suggested that there were two forms of Hamman-Rich syndrome: an acute form and a chronic form. This article laid the foundation for IPF as a distinct disease (the chronic form).
- 1964. Dr. Scadding from the United Kingdom proposed using the term cryptogenic fibrosing alveolitis for the chronic form of Hamman-Rich syndrome. For many years, cryptogenic fibrosing alveolitis was synonymous with idiopathic pulmonary fibrosis.
- 1969. Drs. Leibow and Carrington described 5 histologic subgroups of “chronic idiopathic interstitial pneumonia”, one of which was usual interstitial pneumonitis (UIP).
- 1976. Researchers at the National Institutes of Health, led by Dr. Crystal, proposed that idiopathic pulmonary fibrosis initiates as inflammation in the alveoli of the lungs that later progresses to fibrosis. The basis of this proposed mechanism was the findings of increased inflammatory cells in bronchoalveolar lavage fluid obtained from bronchoscopies performed on patients with IPF.
- 1998. Drs. Katzenstein and Myers proposed that usual interstitial pneumonitis is the lung biopsy finding that occurs in idiopathic pulmonary fibrosis. They determined that the disease is due to excessive fibrosis (scar) and that there is little inflammation.
2001. Dr. Hunninghake and colleagues determined that IPF can be often be diagnosed by the finding of usual interstitial pneumonitis on the chest CT scan, allowing some patients to avoid undergoing a lung biopsy.
What causes idiopathic pulmonary fibrosis?
In 2023, idiopathic pulmonary fibrosis is less idiopathic than it was in the past. IPF can be currently thought of as an auto-fibrotic lung disease due to a combination of inherited genes and environmental factors. An “auto-immune” disease occurs when the body’s immune system turns against itself, such as in systemic lupus erythematosis. An “auto-inflammatory” disease occurs when the body’s inflammatory system turns against itself, such as in the VEXAS syndrome. An “auto-fibrotic” disease is when the body’s scarring system turns against itself. Scar results when wounds heal and as such, auto-fibrotic diseases can be thought of as disorders of uncontrolled wound healing.
There is not one single gene that is responsible for idiopathic pulmonary fibrosis but rather there are many genes that can predispose a person to develop IPF. These genes vary in terms of how strongly they predispose IPF. For example, people with abnormal telomerase genes have a very high risk for developing IPF whereas those with an abnormal MUC5B gene have an increased risk of developing IPF that is not as great as with abnormal telomerase genes. For all of these genes, environmental injury to the lungs significantly increases the chance that a person will ultimately develop IPF. The most common cause of environmental injury is tobacco smoking but respiratory viruses, work-related dust inhalation, air pollution, and chronic gastroesophageal reflux can also increase the chance that a person with an abnormal gene will develop IPF.
How do we know if a drug for IPF works?
The only way to know if a drug against any disease works is by scientific research. But some types of scientific research are more convincing than others. Here are the common categories of research that physicians look at when determining a drug’s effectiveness.
- Case reports. These are usually publications of one or two patients who appeared to respond to some type of treatment. Case reports are the weakest evidence of a drug’s effectiveness but they can be the justification for doing additional future research about a drug.
- Case series. These are publications of numerous patients treated with a drug. Although they can provide stronger evidence than a case reports, they are still overall fairly weak. These are often called “retrospective reviews” meaning that a physician is looking back (retrospective) over a group of patients that the physician has managed in the past.
- Open-label clinical trial. This is when a researcher deliberately gives a group of patients a drug and tracks how they respond to it. There will generally be a specific test that the researcher performs to see if the drug has an impact, for example, by performing pulmonary function tests. When a clinical trial is “open-label”, it means that the researcher and the patients know whether or not they are getting the drug. However, this knowledge can lead to bias by either the patients or the researcher who may want to think that the drug is working, even if it is not.
- Randomized, double-blind, placebo-controlled clinical trial. These provide the strongest evidence that a drug is effective. Patients are randomly assigned to either receive the drug or a placebo and neither the patients nor the researchers know if a particular patient got the drug or got the placebo. In order for these studies to be statistically significant, the studies have to have a large number of patients, typically in the hundreds or thousands.
There are three “phases” of clinical trials of new drugs. The FDA will grant approval if the final phase of a clinical trial shows a statistically significant benefit of the drug without severe side effects.
- Phase 1 trials. These involve a small number of patients and are usually open-label and of short duration. The researchers are primarily interested in drug safety and side effects. Several doses of the drug will be tested in order to find the safest doses and how frequently the drug should be given.
- Phase 2 trials. These involve a larger number of patients who are randomized to receive either the drug or a placebo. During phase 2, the researchers will determine if the drug holds the possibility of being effective and will determine the best dose of the drug to use in the next phase.
- Phase 3 trials. These involve very large numbers of patients – IPF trials typically require more than a thousand subjects. There are usually many hospitals (study sites) involved from multiple states and often from multiple countries. Patients are randomized to receive placebo or the drug and are tested regularly to determine if the drug is effective compared to placebo. Most IPF phase 3 trials require each subject to participate for 1 – 2 years.
IPF treatment over the years
Prior to 2014, there were no drugs that were approved by the FDA to treat idiopathic pulmonary fibrosis. Therefore, physicians used drugs that were approved for other diseases that were already available on the market. This is called “off-label” use of these drugs. Over time, researchers performed clinical trials to determine if these off-label drugs were actually effective and pharmaceutical companies developed new drugs to test in clinical trials. Clinical trials are expensive to perform and most of the clinical trials involving off-label drugs were funded by federal grants from the National Institutes of Health. Clinical trials of newly created drugs are generally funded by pharmaceutical companies. There has been a steady evolution in the treatment of IPF:
- 1970’s – The prevailing belief about the cause of IPF was abnormal inflammation resulting in alveolitis. Thus, the drugs most commonly used to treat IPF were anti-inflammatory drugs, such as the corticosteroid, prednisone. There were no clinical trials to determine the best dose or whether corticosteroids even worked at all.
- 1980’s – After years of watching patients fail to improve with corticosteroids, physicians turned to a more powerful anti-inflammatory drug, cyclophosphamide (Cytoxan) based on case reports and retrospective case series. Cytoxan was largely used as a chemotherapy drug to treat cancer but was also being used to treat auto-immune diseases such as systemic lupus erythematosus (aka, SLE) and granulomatosis with angiitis (aka, Wegener’s granulomatosis). A problem with Cytoxan is that it was very toxic and patients frequently developed low white blood cell counts, bladder hemorrhaging, and bladder cancer.
- 1990’s – After years of dealing with Cytoxan’s side effects, physicians looked to a different drug that was slightly less powerful as an anti-inflammatory drug but had much fewer complications. That drug was azathioprine, or Imuran. This was often given along with the corticosteroid, prednisone. A third drug as also frequently added: N-acetylcysteine (NAC). Because NAC has very few side effects and is available over-the-counter, it was seen as being fairly innocuous and possibly beneficial due to it’s anti-oxidant properties.
- 2000’s – A phase 3 study of azathioprine, prednisone, and NAC found that these drugs were not helpful in IPF and if anything, patients who took them did worse than patients who got the placebo. A small study suggested that gamma interferon might be beneficial and so physicians turned to the off-label use of gamma interferon that was already approved by the FDA for use in a rare condition called chronic granulomatous disease.
- 2010’s – A phase 3 study of gamma interferon showed that it was ineffective in IPF and thus physicians stopped using it. In 2014, large phase 3 trials found that the anti-fibrotic drugs pirfenidone and nintedanib were both effective in IPF, resulting in the FDA approving their use. Presently, these are the only drugs approved for IPF in the U.S. and are considered the current standard of care.
The past 3 decades are littered with drugs that initially held promise but were shown in clinical trials to be ineffective in IPF. A list of the most prominent of these drugs is below:
Current IPF treatment
Pirfenidone and nintedanib have both been shown to slow the progression of IPF compared to placebo, however they do not stop or cure the disease. Think of them as slowing the progression of IPF from 60 miles per hour down to 30 miles per hour. The patients will still ultimately get worse but just more slowly. There has not been a head-to-head comparison of the two drugs but the available evidence suggests that both are equally effective. The choice of which drug to prescribe is generally based on the personal preference of the physician and the patient. These preferences are most commonly based on the differing side effect profiles of the two drugs: pirfenidone cause cause skin rash and sun-sensitivity, nintedanib can cause diarrhea. The drugs also differ in drug-drug interactions – for example, nintedanib interacts with anticoagulants whereas pirfenidone interacts with ciprofloxacin.
Lung transplant is the only curative treatment for IPF. In the U.S., IPF is now the most common indication for lung transplant, accounting for 37%. Not all patients with IPF are eligible for transplant, however. The decision of eligibility is made by each hospital’s transplant team and limiting factors can include active tobacco use, obesity, older age, deconditioning, and presence of other concurrent diseases. Moreover, transplant comes with it’s own risks – 15% of patients with IPF die in the first 12 months after transplant and of those who survive the first 12 months, only 67% are still alive 5 years after transplant. However, post-transplant care is improving and survival rates are expected to improve in the future.
In addition to anti-fibrotic medications and lung transplant, there are other interventions that have been shown to be useful in patients with idiopathic pulmonary fibrosis. Oxygen is effective in improving the quality of life of patients with IPF. It can reduce shortness of breath, improve ability to exercise, and facilitate travel. Pulmonary rehabilitation is also effective in improving quality of life and should be considered for all IPF patients with shortness of breath or exercise limitation. Patients with IPF are at increased risk of obstructive sleep apnea and physicians should have a low threshold for performing sleep studies and prescribing CPAP when indicated. Although treating asymptomatic patients with proton pump inhibitors is ineffective in IPF, whose with symptoms of gastroesphageal reflux should be treated in order to reduce on-going lung injury. Patients with large hiatal hernias may benefit by surgical repair if they are able to tolerate surgery. Smoking cessation is essential to stop on-going lung injury, improve quality of life, and make patients eligible for lung transplant. All patients with IPF should be vaccinated to prevent pneumococcal pneumonia, influenza, respiratory syncytial virus (RSV) and COVID. Patients with IPF are at higher risk of death from respiratory infections and even if they survive the infection, it can result in additional lung injury that can accelerate the progression of IPF. During the first 12 months of the pandemic, 5% of my outpatients with interstitial lung disease died from a COVID infection due to their greater susceptibility.
Although cure of IPF is not yet possible (other than with transplant), it appears that our current treatment approach is making a difference. A recent study from Italy compared patients with IPF over a 15-year period from 2002 to 2016. Over this time, there was an increase in life expectancy, decrease in the rate of hospitalization, and decrease in the rate of acute exacerbations. Correlated with these improved outcomes was an increase in the use of anti-fibrotic drugs (pirfenidone and nintedanib), decrease in the use of anti-inflammatory drugs (corticosteroids, cyclophosphamide, and azathioprine), and increase in the use of bronchoscopic cryobiopsies as opposed to the more invasive surgical lung biopsies.
The future of IPF treatment
Prior to the FDA approval of pirfenidone and nintedanib, most IPF clinical trials compared a promising drug to placebo. Now that pirfenidone and nintedanib are the accepted standard of care, future trials have to either compare new drugs to pirfenidone and nintedanib or have to compare new drugs to placebo in patients who are already taking pirfenidone or nintedanib. Performing clinical trials in IPF is complicated for a number of reasons:
- The heterogeneity of IPF makes trial design difficult. Given that there are multiple predisposing genes involved in IPF and given that there are multiple environmental risks for IPF, no two patients with IPF are exactly alike and treatments that work for one patient may not work for another.
- Mortality cannot be used as an endpoint. The current average survival of a patient with IPF is 5.5 years based on the Italian study. If researchers were to use death as the endpoint in a clinical trial, that trial would have to last for a decade or more in order to recruit a sufficient number of patients and follow them until death. This is too long of a length of time to realistically perform a clinical trial.
- Pulmonary function tests are currently the best outcome measure for IPF clinical trials. We use change in the forced vital capacity and diffusing capacity as markers of the progression of IPF. Although this is appealing from a logical standpoint, PFT changes may not necessarily correlate with life expectancy. But for now, PFTs are the best that we have.
- To be statistically significant, trials must include hundreds of patients. The CAPACITY and ASCEND studies that led to approval of pirfenidone enrolled 1,247 subjects. The IMPULSIS studies that led to the approval of nintedanib enrolled 1,066 subjects. To recruit this many subjects, many study sites are required – the IMPULSIS studies required 205 hospital locations in 24 countries, the CAPACITY studies required 110 hospital locations in 13 countries, and the ASCEND study required 127 hospital locations in 9 countries. Because future trials will need to incorporate multiple treatment arms including those taking pirfenidone, those taking nintedanib, and those taking neither, the number of subjects in future trials will need to be even larger than in previous IPF trials.
- Clinical trials are costly. The average cost to bring a new drug to market, from initial drug discovery to FDA approval is $2.3 billion. Consequently, for pharmaceutical companies to recoup their drug development costs, any new drug is expensive and IPF drugs are no exception. The retail price of pirfenidone is $16,000 per month ($2,200 per month if using coupons such as GoodRx) and the retail price of nintedanib is similar.
There are a number of new drugs currently in phase 1 and phase 2 trials and several of these hold early promise to add to our treatment options for IPF patients. Some of the questions likely to be answered in future IPF treatment research include:
- Is combination therapy more effective than mono therapy? Currently, patients receive either pirfenidone or nintedanib but not both. We do not know if the combination of the two be better than either one alone. The same holds for any new drug that is developed – whether it should be given alone or in combination with one of the two currently approved drugs.
- Is inhaled therapy better than oral therapy? Giving drugs to treat lung disease by inhalation is attractive – it offers the possibility of giving relatively high concentrations of the drug directly to the airways with lower concentrations in the blood. This has the potential to reduce systemic side effects while boosting the effect in the lungs.
- What are the chemical pathways involved in fibrosis? At present, it appears that transforming growth factor-β (TGF-β) is a key player in fibrosis development. Drugs that specifically target TGF-β may be effective in slowing fibrosis. Because TGF-β is secreted as inactive form that is converted to an active form by αvβ6 integrin, this molecule is another attractive target for future treatments. We need to identify the other proteins in the body that are involved in fibrosis.
- Are there biomarkers of IPF that would be better to use in clinical trials than changes in pulmonary function tests? In atherosclerosis, we have a great biomarker in the cholesterol level that allows us to determine if a drug is working without having to wait to see whether or not a patient develops a heart attack or stroke. Measurement of biomarkers that are involved in the chemical pathways of fibrosis would allow us to more quickly tell if a drug is working for a particular patient without having to wait months or years to see if there are changes in pulmonary function tests.
- Can genetics direct treatment? The different genes involved in idiopathic pulmonary fibrosis affect different proteins in the body and each of these proteins has a different role in the development of fibrosis. In lung cancer, we use the genetics of a person’s cancer to choose which chemotherapy will be most effective. As we learn more about the genetics of IPF, it is likely that a person’s specific genetic make-up will help us pick the best treatment for that particular individual.
- What is the role of gene therapy? Gene editing is in its infancy in medicine but is already showing great promise in muscular dystrophy and sickle cell anemia. As we learn more about the genes involved in IPF, we may be able to edit those genes, not only in patients with IPF but also potentially in their relatives with the hope of preventing the onset of IPF in the first place. Because IPF only affects the lungs, it is possible that only the genes of lung tissues would need to be edited, for example, by inhalational techniques.
When I first started specializing in treating IPF 35 years ago, it was my hope to see effective treatments arise during my career. Not only do we now have effective treatments but we also know which medications can actually make patients worse. For these reasons, our management of IPF is much better today than ever before. The treatment will be even better yet in the future with translational research that results in taking the word “idiopathic” out of idiopathic pulmonary fibrosis and clinical research to bring us more effective therapies for patients with IPF.
November 14, 2023