Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.
Identify medicine-related pulmonary injury through a precise exposure timeline, stop dangerous triggers safely and exclude infection, cancer, oedema and underlying disease progression.
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.
Some anticancer, antiarrhythmic and other medicines injure alveolar epithelium or accumulate within lung, with risk influenced by exposure and host reserve.
A drug or metabolite can trigger hypersensitivity pneumonitis, eosinophilic pneumonia, organising pneumonia or vasculitic patterns independent of simple cumulative dose.
Checkpoint inhibitors and other immune-modifying therapies may unleash inflammatory pneumonitis, while immunosuppressive drugs predispose to infections that mimic toxicity.
Prior thoracic radiotherapy, high oxygen exposure and combination regimens can amplify pulmonary injury from particular agents in susceptible patients.
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.
Direct toxicity, oxidative stress or immune activation damages epithelium and endothelium, producing inflammation and capillary leak.
The injury manifests as diffuse alveolar damage, organising pneumonia, eosinophilic disease, fibrosis, airway disease or pleural involvement rather than one specific pattern.
Withdrawal may permit recovery, but severe or repeated injury can organise into persistent fibrosis and impaired gas transfer.
Fever, cough, dyspnoea, hypoxaemia, diffuse opacity and sometimes eosinophilia begin soon after exposure, as can occur with acute nitrofurantoin or daptomycin reactions.
Progressive dry cough and exertional breathlessness over months with reticulation, traction change and falling TLCO may follow long-term nitrofurantoin or amiodarone exposure.
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.
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.
New effusion, pleuritic pain, pulmonary hypertension or thromboembolism may be medicine related, but malignancy, heart failure and thrombosis need direct investigation rather than assumption.
Rash, fever, eosinophilia, liver injury, renal dysfunction or mucosal involvement alongside lung disease raises a multisystem drug reaction and increases urgency.
Fever and new infiltrates during cancer or immune treatment require microbiological assessment because infection is common and immunosuppression could be harmful.
Cancer, autoimmune ILD or chronic lung disease may worsen independently; comparative imaging and the clinical timeline help separate progression from toxicity.
Fluid treatment, renal injury and cardiotoxic drugs can cause hydrostatic oedema, supported by cardiac and volume findings rather than an inflammatory pattern alone.
Cancer and systemic inflammation raise thrombotic risk, so acute dyspnoea or hypoxaemia still warrants probability-led embolism assessment.
Change conforming to a radiation field with appropriate timing suggests radiotherapy injury, though recall reactions and combined toxicity can blur boundaries.
Diffuse alveolar injury can rapidly cause severe hypoxaemia, low compliance and need for critical-care support, adding morbidity beyond the initial pulmonary disorder.
Incomplete repair may leave irreversible matrix deposition, restriction, reduced gas transfer and chronic oxygen need, and increasing the burden of otherwise local respiratory disease.
Suspected toxicity may require interruption of effective cancer, cardiac or immune treatment, creating competing disease risks.
Treatment of presumed inflammatory toxicity can cause infection and metabolic complications when diagnosis, dose or duration is inappropriate.
Re-exposure may provoke faster or more severe injury, so any rechallenge needs specialist risk assessment and close surveillance.
Nitrofurantoin may cause an early hypersensitivity illness or a chronic fibrotic syndrome; amiodarone toxicity can appear after long exposure and progress after withdrawal.
Organising pneumonia or diffuse alveolar damage on HRCT narrows mechanism and severity, but the medicine link still depends on timing and exclusion of alternatives.
Rheumatoid arthritis, cancer and infection can each explain infiltrates in the same patient receiving methotrexate or immunotherapy. Causal confidence should be stated, not implied.
Stopping amiodarone, immunosuppression or anticancer treatment may have serious consequences; urgent coordination is safer than either blindly continuing or silently discontinuing it.
Recurrence may be more rapid and severe. Re-exposure is justified only rarely when benefit is compelling and specialist monitoring is explicit.
Rejecting a medicine cause because the drug was started years before symptoms.
Blaming the newest prescription without reviewing hospital infusions, radiation, oxygen exposure and older cumulative treatments.
Calling ground-glass opacity drug pneumonitis before microbiological and cardiac assessment in an immunosuppressed patient.
Continuing nitrofurantoin despite new pulmonary-damage symptoms contrary to current MHRA safety advice.
Stopping a life-preserving antiarrhythmic or cancer drug without urgent coordination with the responsible specialist.
Rechallenging to prove causality without a documented expert risk-benefit decision and monitoring plan.
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An older adult taking long-term nitrofurantoin develops new dry cough, progressive breathlessness and bilateral interstitial change. What action best reflects MHRA advice?
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.
Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes
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.
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.