This study is open to children and adolescents aged 2 to 17 years with interstitial lung disease (ILD). Nerandomilast has just been approved in some countries to help adults with a lung condition called idiopathic pulmonary fibrosis. The purpose of this study is to understand how nerandomilast is tolerated and handled by the body and whether nerandomilast also helps children and adolescents with ILD.

For participants aged 6 to 17 years when joining, the study has 2 parts. In the first part, participants are put into 1 of 2 groups randomly, which means by chance. One group gets nerandomilast and the other group placebo. Placebo looks like nerandomilast but does not contain any medicine.

Participants are twice as likely to be in the nerandomilast group. They take tablets twice a day for 6 months. After these 6 months, in the second part of this study, they get nerandomilast for at least 2 years regardless of what they got in the first part.

Young participants aged 2 to 5 years when joining get nerandomilast from the start. They receive tablets twice a day for at least 2 and a half years.

Depending on when a person joins, the study lasts between 2 and a half years and up to 5 years. During this time, participants may visit the study site about 18 to 30 times. Study doctors collect blood samples to check participants' health and to find out how their body handles the study medicine. Doctors also check the function of the lungs, body growth, and how participants feel. The study doctors also regularly check participants' health and take note of any changes. For participants aged 6 to 17 years, the results are compared between the groups to see whether nerandomilast treatment helps children and adolescents.

Inclusion Criteria:

• Children and adolescents 2 to <18 years old at Visit 2.

• Participants with evidence of fibrosing ILD on high-resolution computed tomography (HRCT) within 12 months of Visit 1 as assessed by the investigator and confirmed by central review.

• For children ≥6 years: Participants with forced vital capacity (FVC) % predicted ≥25% at Visit 2.

• Participants with clinically significant fibrosing ILD at Visit 2, as assessed by the investigator based on any of the following:

  • Fan score ≥3, or

  • Documented evidence of clinical progression over time based on either

    • a 5-10% relative decline in FVC % predicted accompanied by worsening symptoms, or
    • a ≥10% relative decline in FVC % predicted, or
    • increased fibrosis on HRCT, or
    • other measures of clinical worsening attributed to progressive lung disease (e.g. increased oxygen requirement, decreased diffusion capacity).

Further inclusion criteria apply.

Exclusion Criteria:

• Previous treatment with nerandomilast.
• Participants treated with other oral/systemic PDE4 and non-selective PDE inhibitors within 30 days before Visit 1.
• Participants treated with pirfenidone in the 8 weeks prior to Visit 1.
• Unstable pulmonary arterial hypertension (PAH).
• Active vasculitis, unstable or uncontrolled within 8 weeks prior to Visit 1 or during the screening period.
• Any suicidal behaviour (i.e. actual attempt, interrupted attempt, aborted attempt, or preparatory acts or behaviour) in the past (lifetime).
• Any suicidal ideation of type 4 or 5 on the columbia suicidal severity rating scale (C-SSRS) in the past 3 months at Visit 1 or at Visit 2 (i.e. active suicidal thought with method and intent but without specific plan; or active suicidal thought with method, intent, and plan).
• Participants with clinically significant depression symptoms defined as the short version of mood and feeling questionnaire (SMFQ) score ≥8.

Further exclusion criteria apply.

Once the criteria in section "Time Frame" are fulfilled, researchers can use the following link https://www.clinicalstudies.boehringer-ingelheim.com/msw/datasharing to request access to the clinical study documents regarding this study, and upon a signed "Document Sharing Agreement".

Furthermore, researchers can request access to the clinical study data, for this and other listed studies, after the submission of a research proposal and according to the terms outlined in the website.

One year after the approval has been granted by major Regulatory Authorities and after the primary manuscript has been accepted for publication, or after termination of the development program.

For study documents - upon signing of a 'Document Sharing Agreement'.

For study data - 1. after the submission and approval of the research proposal (checks will be performed by the sponsor and/or the independent review panel, including checking that the planned analysis does not compete with sponsor's publication plan); 2. and upon signing of a legal agreement.

Masking applies to double-blind part of the trial.