Drug-induced interstitial lung disease

The interstitium is the thin lattice of tissue between the air sacs and blood vessels. In drug-induced disease, a medicine or its breakdown product triggers an immune or toxic reaction in that tissue. Patterns include inflammation (pneumonitis), eosinophilic lung disease, organising pneumonia and, in some cases, progressive fibrosis. Which pattern occurs depends on the drug, the dose and the person.

Asthma + Lung UK describes ILD as over 200 conditions affecting lung tissue rather than airways, with some causing inflammation, some scarring and some both. Drug-induced disease is one of the rarer, but treatable, subtypes.

Cancer treatments are the best known group, including some chemotherapy agents and newer immunotherapy and targeted drugs. Certain antibiotics, some medicines for heart rhythm, medicines for inflammatory arthritis and some immunosuppressants have also been linked. The risk for any individual medicine is generally low, and the benefits of treatment usually far outweigh it, so most people never experience this.

Risk is higher with pre-existing lung disease, older age, combined treatments, previous chest radiotherapy and kidney impairment that raises drug levels. Teams therefore sometimes arrange baseline breathing tests before starting a high-risk treatment and monitor symptoms during it.

• Some chemotherapy and immunotherapy medicines.

• Certain antibiotics and anti-arrhythmic medicines.

• Some disease-modifying drugs used in rheumatoid arthritis.

• Immunosuppressants used after transplant or in autoimmune disease.

Symptoms usually develop over days to weeks, though they can appear after months or years of treatment. Breathlessness that gets worse after movement or exercise is the key feature the charity describes, with persistent cough, fatigue and sometimes weight loss. Because these overlap with infection, heart failure and the underlying illness, the link to the medicine can be missed.

Contact your prescriber, specialist nurse or NHS 111 promptly about new or worsening breathlessness, dry cough or fever on a high-risk medicine, and call 999 for severe breathlessness, blue lips or chest pain.

There is no single test. Doctors build the diagnosis from the story, including the timing of a medicine start, the exclusion of infection and heart causes, and imaging. A high-resolution CT scan shows patterns of lung involvement. Lung function tests show reduced volumes and gas transfer, and blood tests look for infection and eosinophils. Bronchoscopy with washings may be used to exclude infection, and a biopsy is reserved for unclear cases. Specialists in interstitial lung disease, usually through a multidisciplinary team, review the findings.

The cornerstone is to withdraw the suspected drug when safe, in discussion with the specialist managing the original condition, since stopping a cancer or transplant treatment has its own risks. Corticosteroids are used for moderate or severe inflammatory forms. Oxygen and rehabilitation help symptoms in more advanced cases.

Many people improve over weeks to months after withdrawal. Where scarring has developed, breathlessness may persist, and monitoring continues. A confirmed reaction should be recorded in your notes as an adverse drug reaction and reported through the MHRA Yellow Card scheme, and the medicine is normally avoided in future.