Drug-Induced & Radiation Lung Injury
Stop the culprit, exclude the mimics, and know when steroids help
Recognizing drug and radiation lung injury
Timing is the clue. Suspect the treatment when cough, dyspnea, hypoxemia or new infiltrates appear weeks to months after a drug is started or after thoracic radiotherapy. No imaging or biopsy pattern is specific: drugs can produce nonspecific interstitial pneumonia, organizing pneumonia, hypersensitivity pneumonitis, eosinophilic pneumonia, diffuse alveolar damage resembling ARDS, or noncardiogenic pulmonary edema.
A diagnosis of exclusion. First rule out infection (Pneumocystis, CMV and fungi in anyone on chemotherapy, methotrexate or steroids), cardiogenic edema (BNP, echocardiography), pulmonary embolism and cancer progression such as lymphangitic spread. HRCT defines the pattern, PFTs usually show restriction with a low DLCO, and bronchoscopy with BAL mainly serves to exclude infection.
- Build a timelineprescribed, over-the-counter and vaped products, plus prior radiation
- Exclude mimicsinfection, heart failure, pulmonary embolism, tumor progression
- Stop the offending agentthe key intervention; avoid rechallenge
- Add glucocorticoidsfor moderate–severe or progressive disease, tapered over weeks to months
Amiodarone and bleomycin
Amiodarone. Toxicity tracks dose (risk rises at ≥400 mg/day) and cumulative exposure and is more likely with older age and preexisting lung disease. Months into therapy the patient develops dry cough, dyspnea, weight loss, low-grade fever and patchy or interstitial infiltrates that can progress to fibrosis. Because the drug is iodine-rich, involved lung, liver and spleen look high-attenuation on CT; foamy macrophages in BAL (phospholipidosis) confirm exposure, not toxicity. Baseline chest radiograph and PFTs with DLCO are obtained before therapy. A DLCO fall of roughly 20% or more with new infiltrates supports toxicity once heart failure, a common mimic in these cardiac patients, and infection are excluded. Treatment is discontinuation plus prednisone about 40–60 mg/day tapered over months; the 1–2-month half-life makes recovery slow, and a rushed taper invites relapse.
Bleomycin. Lung and skin contain little bleomycin hydrolase, the inactivating enzyme, so iron-dependent free radicals injure capillary endothelium and type I pneumocytes, producing basilar crackles and fibrosis. Risk rises with cumulative dose above 400 units, age over 70, renal impairment (the drug is renally cleared), smoking and chest radiation. Serial DLCO is the monitoring test and may fall before symptoms. Bleomycin belongs to ABVD (Hodgkin lymphoma) and BEP (germ cell tumors), causes flagellate hyperpigmentation, and is minimally myelosuppressive; the doxorubicin in ABVD is the reason for echocardiographic monitoring.
High FiO2 amplifies bleomycin injury and can precipitate acute pneumonitis or ARDS long after treatment ends. In exposed patients, including during anesthesia, use the lowest FiO2 that keeps SpO2 near 88–92%.
Other classic culprit drugs
| Drug | Timing and setting | Clues | Management |
|---|---|---|---|
| Methotrexate | Usually first year; idiosyncratic, not dose-related | Fever, dry cough, hypoxemia, bilateral interstitial infiltrates, ± eosinophilia; lymphocytic inflammation with poorly formed granulomas | Exclude PJP; stop permanently; steroids |
| Nitrofurantoin, acute | Days to weeks after starting | Fever, rash, eosinophilia, basilar infiltrates ± small effusions | Stop; improves within days |
| Nitrofurantoin, chronic | Months to years of UTI prophylaxis, usually older women | Insidious dyspnea, interstitial fibrosis, sometimes hepatitis | Stop; steroids if severe; recovery often incomplete |
| Busulfan | Months to years; HSCT conditioning, formerly CML | Interstitial fibrosis ("busulfan lung") | Stop; largely supportive |
| Nitrosoureas (carmustine/BCNU, lomustine) | Cumulative dose; carmustine injury can surface years later | Fibrosis, often upper lobe after childhood brain-tumor therapy | Largely supportive |
Associated clues. Busulfan also causes skin hyperpigmentation, an Addison-like wasting syndrome, seizures (high-dose regimens include prophylaxis) and hepatic sinusoidal obstruction syndrome. Folic acid does not prevent methotrexate pneumonitis. The Beers criteria advise against long-term nitrofurantoin suppression in older adults. Other agents to recognize: cyclophosphamide, gemcitabine, taxanes and mTOR inhibitors (pneumonitis), daptomycin (eosinophilic pneumonia), and opioid or salicylate overdose (noncardiogenic pulmonary edema).
Checkpoint-inhibitor pneumonitis
Who and when. PD-1 and PD-L1 inhibitors (pembrolizumab, nivolumab, atezolizumab, durvalumab) cause pneumonitis in roughly 3–5% of patients, more often when combined with the anti-CTLA-4 antibody ipilimumab and in lung cancer. Onset is usually within the first few months, and CT most often shows an organizing-pneumonia or ground-glass pattern. After infection and tumor progression are excluded, management follows the severity grade:
- Grade 1 (imaging only): hold the drug or continue with close monitoring and repeat imaging.
- Grade 2 (symptomatic): hold the drug; prednisone 1–2 mg/kg/day, tapered over at least 4–6 weeks.
- Grade 3–4 (hypoxemia, severe or life-threatening): discontinue permanently, admit, give IV methylprednisolone 1–2 mg/kg/day; if no improvement in 48 hours, add infliximab, mycophenolate or IVIG.
Prolonged high-dose steroids warrant Pneumocystis prophylaxis.
Radiation pneumonitis and fibrosis
Radiation pneumonitis. Dry cough, dyspnea and low-grade fever follow radiotherapy for lung, breast or esophageal cancer or lymphoma. The telltale opacity is confined to the treatment port, with straight margins that cross fissures and segments instead of following anatomy. Risk rises with the volume of lung irradiated and with concurrent chemotherapy; asymptomatic imaging changes need no treatment.
| Feature | Radiation pneumonitis | Radiation fibrosis |
|---|---|---|
| Onset | 4–12 weeks after RT | Evolves from 6–12 months; stable by ~2 years |
| Imaging | Ground glass or consolidation with straight, in-field borders | Dense, sharply marginated scarring, volume loss, traction bronchiectasis, hilar or mediastinal retraction toward the field |
| Reversibility | Usually resolves | Permanent |
| Treatment | If symptomatic, prednisone about 40–60 mg/day with a slow taper | Supportive: oxygen, pulmonary rehabilitation; steroids do not help |
Radiation recall: a later drug (gemcitabine, taxanes, anthracyclines, checkpoint inhibitors) can reignite pneumonitis sharply confined to an old radiation field. Breast irradiation can also trigger steroid-responsive organizing pneumonia that migrates outside the field.
Vaping-associated lung injury (EVALI)
Presentation. EVALI follows vaping within the prior 90 days, mostly of illicit THC cartridges; vitamin E acetate, a thickening additive, was found in BAL fluid of most patients in the 2019 outbreak. Young patients present with cough, dyspnea and chest pain plus prominent GI symptoms (nausea, vomiting, diarrhea), fever and hypoxemia. CT shows bilateral ground-glass opacities, often with subpleural sparing.
Management. It is a diagnosis of exclusion: test for influenza, COVID-19 and bacterial pneumonia, and cover empirically until infection is excluded. Admit if SpO2 is below 95% on room air, give systemic glucocorticoids, insist on stopping vaping, and arrange early follow-up because relapse occurs. Vaping can also provoke acute eosinophilic pneumonia, which BAL eosinophilia distinguishes. Diacetyl, a flavoring chemical, is linked to bronchiolitis obliterans in popcorn-factory workers, not to EVALI.