How Do Antifibrotics Work for Interstitial Lung Disease?

Antifibrotic medications, such as nintedanib and pirfenidone, are treatments designed to slow down the progression of selected interstitial lung diseases (ILD). They do not cure the disease or reverse existing lung scarring, but they act like a “brake” on the scarring process ^[1]. By interfering with the chemical signals that cause the body to produce excess scar tissue, these drugs help preserve your current lung function and slow down future damage ^[2].

The Goal: Slowing Disease Progression

When you have a progressive fibrosing ILD, signaling in the lungs can keep scar-forming cells active. Over time, this makes the lungs stiff and reduces your Forced Vital Capacity (FVC)—the amount of air you can forcefully exhale after taking a full breath in ^[3].

The primary goal of antifibrotic medications is to slow the rate at which your FVC declines over time ^[4]. In clinical trials, these medications have been shown, on average, to reduce the annual loss of lung function compared to patients taking a placebo ^[3][5].

It is important to understand that antifibrotics cannot dissolve or remove established scar tissue ^[1]. Chronic fibrotic changes seen on a lung scan are generally permanent ^[6][7]. However, not all changes on a scan are permanent scars—some inflammation may improve if the underlying cause of your ILD is treated. Because antifibrotics do not reverse scarring, you may not “feel better” when taking them ^[7]. Success is measured by serial trends in your FVC, symptoms, and oxygen needs showing a slower decline ^[2]. It can be discouraging to take a daily medication without feeling an immediate physical improvement, but staying on therapy helps protect your future breathing capacity ^[2].

Who May Be Offered These Medications?

Nintedanib and pirfenidone are not interchangeable, and they are not appropriate for every type of ILD.

• Nintedanib (Ofev): Has established clinical evidence and regulatory approval for Idiopathic Pulmonary Fibrosis (IPF) and for certain other progressive pulmonary fibrosis (PPF) conditions ^[3][8].
• Pirfenidone (Esbriet): Is primarily established and approved for IPF. While it is sometimes used off-label for other progressive fibrosing ILDs, the evidence in non-IPF conditions is more limited and requires further research ^[8][9].

Your treatment choice depends on your specific diagnosis, evidence that your disease is progressing, and your other health conditions. Many ILDs (like those caused by autoimmune diseases) require their own specific treatments to address the underlying cause ^[8].

Safety, Monitoring, and Practical Differences

Taking an antifibrotic requires careful monitoring and partnership with your care team. Never stop or change your dose without consulting your doctor.

• Liver Monitoring: Both medications can elevate liver enzymes, requiring baseline and regular follow-up liver blood tests ^[4].
• Nintedanib Precautions: Common side effects include prominent gastrointestinal issues, particularly diarrhea ^[4][10]. It also carries specific warnings regarding risks of bleeding, cardiovascular events, gastrointestinal perforation, and fetal harm.
• Pirfenidone Precautions: Common side effects include nausea, weight loss, fatigue, and significant sun sensitivity (photosensitivity) ^[4][10]. Strict sun protection and protective clothing are required when outside.

How They Work in the Body

While both drugs aim to reduce scarring, they modulate different pathways. Much of what we know about how they work on a cellular level comes from preclinical and laboratory studies.

• Nintedanib: Is a targeted therapy that can inhibit specific chemical receptors (VEGF, PDGF, and FGF) ^[11]. These growth factors are abnormally high in fibrosing ILD ^[12]. By blocking them, nintedanib is thought to reduce the ability of fibroblasts (scar-forming cells) to multiply, migrate, and produce excess collagen ^[13][14].
• Pirfenidone: Its exact mechanism is not completely understood. Experimental evidence suggests it modulates TGF-beta, a major pro-scarring signal ^[15]. It is also proposed to have anti-inflammatory and antioxidant properties that help reduce the production of collagen and fibronectin, the building blocks of scar tissue ^[16][17].