Drug-induced lung disease

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Almost every lung compartment can be injured by medicine. Direct toxicity, immune reaction, oxidative injury, altered fluid balance and infection caused by immunosuppression can produce indistinguishable symptoms and HRCT patterns. The same medicine may cause several phenotypes, and the same pattern may have many medicines or non-drug causes. Safe diagnosis therefore begins with a timeline and a severity assessment, not a memorised list or a single radiology label.

Key agents include amiodarone, nitrofurantoin, methotrexate, bleomycin, immune checkpoint inhibitors, targeted cancer therapies, some antimicrobials and biological agents. Risk changes with cumulative exposure, age, renal function, oxygen exposure, radiation and pre-existing lung disease, depending on the agent. Latency varies enormously. A medicine tolerated for years is not automatically innocent, while a newly prescribed agent is not automatically guilty.

Management is agent and phenotype specific. Stop or withhold the likely culprit when the pulmonary risk outweighs the reason for treatment, but coordinate promptly when the medicine prevents arrhythmia, graft rejection or cancer progression. Support gas exchange, treat confirmed infection, and use corticosteroids only when inflammatory toxicity is sufficiently likely and the drug-specific protocol supports them. Rechallenge can produce severe recurrence and belongs to an expert risk-benefit decision, never an informal test.

Key points

Drug-induced lung disease is a causal diagnosis built from phenotype, timing, exclusion of alternatives and response to withdrawal; there is no universal confirmatory test.
Pulmonary toxicity may appear within hours or only after years, and can worsen after stopping a medicine with a long tissue half-life.
Obtain all prescription, hospital, oncology, infusion, over-the-counter, herbal and recreational exposures with start, dose-change and stop dates.
Common patterns include interstitial pneumonitis, organising pneumonia, eosinophilic pneumonia, diffuse alveolar damage, pulmonary oedema, haemorrhage, pleural disease and pulmonary hypertension.
Amiodarone can cause serious, potentially life-threatening lung toxicity with insidious onset; CT is useful when it is suspected.
Nitrofurantoin can cause acute or chronic pulmonary reactions, and MHRA advises immediate discontinuation when pulmonary damage symptoms occur.
Methotrexate pneumonitis is different from rheumatoid-arthritis associated ILD; infection and the underlying inflammatory disease remain important competing explanations.
Checkpoint-inhibitor and targeted-therapy pneumonitis follows agent-specific grading and stop rules; contact oncology before unsupervised rechallenge or steroid taper.
Improvement after withdrawal supports causality, but corticosteroids, concurrent antibiotics and the natural disease course can confound the apparent dechallenge.
Record the suspected reaction clearly, communicate it to primary and specialist care, and submit an MHRA Yellow Card when appropriate.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Direct toxic injury

Some anticancer, antiarrhythmic and other medicines injure alveolar epithelium or accumulate within lung, with risk influenced by exposure and host reserve.

Immune-mediated reaction

A drug or metabolite can trigger hypersensitivity pneumonitis, eosinophilic pneumonia, organising pneumonia or vasculitic patterns independent of simple cumulative dose.

Treatment-related immune change

Checkpoint inhibitors and other immune-modifying therapies may unleash inflammatory pneumonitis, while immunosuppressive drugs predispose to infections that mimic toxicity.

Radiation and oxygen interaction

Prior thoracic radiotherapy, high oxygen exposure and combination regimens can amplify pulmonary injury from particular agents in susceptible patients.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Pulmonary exposure
A medicine, metabolite or treatment-induced immune response reaches alveolar, airway, vascular or pleural tissue, which links the underlying lesion to the observed respiratory dysfunction.
2
Cellular injury
Direct toxicity, oxidative stress or immune activation damages epithelium and endothelium, producing inflammation and capillary leak.
3
Patterned lung response
The injury manifests as diffuse alveolar damage, organising pneumonia, eosinophilic disease, fibrosis, airway disease or pleural involvement rather than one specific pattern.
4
Resolution or remodelling
Withdrawal may permit recovery, but severe or repeated injury can organise into persistent fibrosis and impaired gas transfer.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Acute hypersensitivity reactionRed flag

Fever, cough, dyspnoea, hypoxaemia, diffuse opacity and sometimes eosinophilia begin soon after exposure, as can occur with acute nitrofurantoin or daptomycin reactions.

Chronic fibrotic toxicity

Progressive dry cough and exertional breathlessness over months with reticulation, traction change and falling TLCO may follow long-term nitrofurantoin or amiodarone exposure.

Oncology pneumonitisRed flag

New cough, hypoxaemia or ground-glass and organising opacities during immune checkpoint, antibody-drug conjugate or targeted therapy must enter the medicine-specific oncology pathway quickly.

Diffuse alveolar haemorrhageRed flag

Falling haemoglobin, haemoptysis that may be absent, diffuse opacities and hypoxaemia during anticoagulant, cytotoxic or immune therapy requires emergency assessment and reversal or treatment planning.

Pleural or vascular toxicity

New effusion, pleuritic pain, pulmonary hypertension or thromboembolism may be medicine related, but malignancy, heart failure and thrombosis need direct investigation rather than assumption.

Systemic adverse-reaction cluesRed flag

Rash, fever, eosinophilia, liver injury, renal dysfunction or mucosal involvement alongside lung disease raises a multisystem drug reaction and increases urgency.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Reconciled medicine timelineFirst step
Why
Identify plausible agents, latency, cumulative exposure and rechallenge.
Interpretation and limitations
Include infusions, intermittent antimicrobials, radiation, oxygen exposure and non-prescribed products. Cross-check records because patients may not recognise hospital-administered treatment as medicine.
02
Chest radiograph and HRCT
Why
Characterise injury pattern and competing diagnoses.
Interpretation and limitations
Ground glass, consolidation, nodules, septal thickening, fibrosis or effusions are nonspecific. Distribution can suggest organising, eosinophilic or diffuse-alveolar-damage phenotypes but rarely names the drug.
03
Full blood count, renal, liver and inflammatory tests
Why
Find eosinophilia, organ toxicity, infection clues and dosing risks.
Interpretation and limitations
Abnormalities may support a systemic drug reaction, affect clearance or suggest another disease. Normal results do not exclude isolated pulmonary toxicity.
04
Microbiology and immune-status assessment
Why
Exclude infection before corticosteroids or further immunosuppression.
Interpretation and limitations
Select bacterial, viral, fungal and opportunistic testing from exposure and immune status. Fever and ground glass in an immunosuppressed patient cannot be assumed sterile.
05
Pulmonary function and oxygenation
Why
Measure physiological impact and recovery after withdrawal.
Interpretation and limitations
A reduced TLCO can be an early abnormality but is nonspecific. Serial improvement supports dechallenge only when infection, oedema and underlying disease are considered.
06
Bronchoscopy or biopsy in selected cases
Why
Exclude infection, haemorrhage, tumour or another ILD when uncertainty changes care.
Interpretation and limitations
Lavages may show lymphocytes or eosinophils without naming the agent. Histology often identifies a reaction pattern rather than proving pharmacological causality.
07
Drug-specific cardiac or oncology review
Why
Coordinate safe withdrawal and assess systemic toxicity.
Interpretation and limitations
For amiodarone review rhythm indication, thyroid and liver status; for cancer therapy use the exact SmPC and oncology grading pathway because hold and permanent-stop rules differ.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Opportunistic infection

Fever and new infiltrates during cancer or immune treatment require microbiological assessment because infection is common and immunosuppression could be harmful.

Underlying disease progression

Cancer, autoimmune ILD or chronic lung disease may worsen independently; comparative imaging and the clinical timeline help separate progression from toxicity.

Cardiogenic pulmonary oedema

Fluid treatment, renal injury and cardiotoxic drugs can cause hydrostatic oedema, supported by cardiac and volume findings rather than an inflammatory pattern alone.

Pulmonary embolism

Cancer and systemic inflammation raise thrombotic risk, so acute dyspnoea or hypoxaemia still warrants probability-led embolism assessment.

Radiation pneumonitis

Change conforming to a radiation field with appropriate timing suggests radiotherapy injury, though recall reactions and combined toxicity can blur boundaries.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01RecognitionConstruct a defensible drug linkFirst stepNew respiratory symptoms or imaging abnormalities occur during or after a potentially pneumotoxic medicine.

1Assess severity and withhold the suspected medicine if clinically safe, seeking immediate prescribing-specialty advice when withdrawal could destabilise arrhythmia, cancer or another serious disease.
2Build a dated exposure table and define the respiratory phenotype with HRCT, physiology and laboratory tests rather than matching one drug to one image.
3Investigate infection, oedema, embolism, malignancy progression and the underlying inflammatory disease in parallel; use bronchoscopy when it changes treatment safety.
4Document causality confidence, communicate across care settings and report a serious or medically significant suspicion through the MHRA Yellow Card scheme.

02Acute toxicityStop injury and support gas exchangeHypoxaemia, diffuse infiltrates or rapid deterioration suggests severe pulmonary reaction.

1EscalationUse an ABCDE assessment, prescribe oxygen to the appropriate target and obtain early respiratory-critical-care support for escalating oxygen requirement or exhaustion.
2Immediately stop nitrofurantoin when pulmonary damage is suspected; for other agents apply the current SmPC and specialist emergency protocol while obtaining microbiological samples.
3Start corticosteroids only when an inflammatory drug reaction is sufficiently likely and serious infection has been addressed; dose and taper follow the agent-specific pathway.
4AlternativeEscalationReassess oxygenation, imaging and organ function frequently, and escalate if withdrawal does not produce the expected direction because long half-life or an alternative diagnosis may explain deterioration.

03AftercarePrevent accidental re-exposureA suspected drug-induced pulmonary reaction has stabilised.

1Record the generic and brand drug, reaction phenotype, severity, timing and certainty in discharge information and the shared medication record.
2Tell the patient which symptoms need urgent review and whether the medicine should be avoided permanently; distinguish allergy labels from other toxic reactions accurately.
3Arrange physiology and imaging follow-up to document resolution or residual fibrosis and review corticosteroid toxicity if treatment was required.
4AlternativeAny proposed rechallenge must be an explicit specialist MDT decision with an alternative-benefit analysis and a monitored stop plan, not a casual diagnostic experiment.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

Removes a recognised cause of acute hypersensitivity reactions and chronic pulmonary injury.

Withdrawal of nitrofurantoin

No taper is required: MHRA advises immediate discontinuation if new or worsening symptoms of pulmonary damage occur, with prompt clinical investigation and an alternative antimicrobial plan where infection treatment remains necessary.

Coordinate treatment of the original urinary indication and assess hepatic injury as well as lung disease. Re-exposure after a serious suspected reaction may cause recurrence; record and communicate the event and submit a Yellow Card.

Suppresses clinically important inflammatory pneumonitis, organising pneumonia or eosinophilic drug reaction when withdrawal and support alone are insufficient.

Prednisolone for selected inflammatory toxicity

There is no cross-drug regimen; an experienced respiratory, oncology or prescribing specialist selects the daily dose and taper from reaction grade, agent SmPC, infection assessment and local protocol.

Steroids can worsen occult infection and obscure diagnosis. Monitor glucose, mood, blood pressure, bone and opportunistic-infection risk; too-rapid taper may cause relapse with some oncology pneumonitis, while non-response demands diagnostic review.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Acute respiratory failure

Diffuse alveolar injury can rapidly cause severe hypoxaemia, low compliance and need for critical-care support, adding morbidity beyond the initial pulmonary disorder.

Progressive fibrosis

Incomplete repair may leave irreversible matrix deposition, restriction, reduced gas transfer and chronic oxygen need, and increasing the burden of otherwise local respiratory disease.

Loss of essential therapy

Suspected toxicity may require interruption of effective cancer, cardiac or immune treatment, creating competing disease risks.

Corticosteroid and immune-treatment harm

Treatment of presumed inflammatory toxicity can cause infection and metabolic complications when diagnosis, dose or duration is inappropriate.

Rechallenge recurrence

Re-exposure may provoke faster or more severe injury, so any rechallenge needs specialist risk assessment and close surveillance.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Trend respiratory rate, oxygen need and imaging closely in acute toxicity, involving critical care before physiological reserve is exhausted.
Use serial spirometry and TLCO to document recovery or residual fibrosis, but interpret change with haemoglobin, infection and underlying disease.
For long-term nitrofurantoin, MHRA advises close vigilance for new respiratory symptoms, especially in older people, plus periodic hepatic assessment.
During amiodarone treatment, maintain regular clinical supervision and investigate new or progressive respiratory symptoms promptly rather than relying on routine radiographs alone.
Follow the exact laboratory, ECG, imaging and steroid-taper requirements of the culprit medicine and prescribing specialty.
Verify that the reaction and re-exposure advice have reached the GP, pharmacy, specialist team and patient-held medication information.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Latency is not uniform

Nitrofurantoin may cause an early hypersensitivity illness or a chronic fibrotic syndrome; amiodarone toxicity can appear after long exposure and progress after withdrawal.

The scan names a pattern

Organising pneumonia or diffuse alveolar damage on HRCT narrows mechanism and severity, but the medicine link still depends on timing and exclusion of alternatives.

Underlying disease competes

Rheumatoid arthritis, cancer and infection can each explain infiltrates in the same patient receiving methotrexate or immunotherapy. Causal confidence should be stated, not implied.

Withdrawal can itself be risky

Stopping amiodarone, immunosuppression or anticancer treatment may have serious consequences; urgent coordination is safer than either blindly continuing or silently discontinuing it.

Rechallenge is not a bedside test

Recurrence may be more rapid and severe. Re-exposure is justified only rarely when benefit is compelling and specialist monitoring is explicit.

11Common pitfallsFrequent interpretation and management errors.

01
Rejecting a medicine cause because the drug was started years before symptoms.
02
Blaming the newest prescription without reviewing hospital infusions, radiation, oxygen exposure and older cumulative treatments.
03
Calling ground-glass opacity drug pneumonitis before microbiological and cardiac assessment in an immunosuppressed patient.
04
Continuing nitrofurantoin despite new pulmonary-damage symptoms contrary to current MHRA safety advice.
05
Stopping a life-preserving antiarrhythmic or cancer drug without urgent coordination with the responsible specialist.
06
Rechallenging to prove causality without a documented expert risk-benefit decision and monitoring plan.