What drug can cause pneumonia? Understanding medication-induced lung injury

October 7, 2025 •

3 min read

While rare, accounting for an estimated 3-5% of all interstitial lung disease cases, drug-induced lung injury can present as inflammation that mimics infectious pneumonia. Understanding what drug can cause pneumonia is crucial for timely diagnosis, as many medications, including certain chemotherapy agents, antibiotics, and heart drugs, are implicated.

Quick Summary

Several drug classes, including chemotherapy, heart rhythm medications, and immunosuppressants, can cause lung inflammation or increase infection risk, potentially leading to drug-induced pneumonia.

Key Points

Drug-Induced vs. Infectious Pneumonia: Drug-induced lung inflammation, or pneumonitis, can mimic infectious pneumonia and is primarily a diagnosis of exclusion.
Chemotherapy Risks: Medications used in chemotherapy and immunotherapy, such as bleomycin, methotrexate, and checkpoint inhibitors, are frequent causes of pulmonary toxicity.
Amiodarone Toxicity: The heart medication amiodarone is notoriously linked to lung toxicity, which can occur at any dose and at various points during treatment.
Immunosuppression and Infection: Immunosuppressant drugs increase a patient's risk of developing opportunistic infections like Pneumocystis jirovecii pneumonia due to a weakened immune system.
Discontinuation is Key: The main treatment for drug-induced lung injury is to immediately stop the implicated medication, often with supportive care and sometimes corticosteroids in severe cases.
Patient-Specific Risk Factors: Factors like older age, pre-existing lung disease, smoking history, and cumulative drug dosage can increase an individual's risk of experiencing drug-induced lung problems.

Introduction to Drug-Induced Pulmonary Disease

Drug-induced pulmonary disease (DIPD) is a broad category of lung disorders caused by an adverse reaction to a medication or substance. When this reaction involves inflammation of the lung tissue, it is often referred to as drug-induced pneumonitis, which can be clinically and radiologically indistinguishable from infectious pneumonia. DIPD can manifest in various ways, from mild symptoms to severe, life-threatening respiratory failure. The diagnosis is often challenging and involves ruling out other potential causes, such as infection or the underlying disease itself. Being aware of the medications associated with this risk is the first step toward recognition and management.

Medication Classes Implicated in Lung Injury

Numerous types of drugs have been linked to pulmonary toxicity, with some posing a greater risk than others. The mechanisms can involve direct toxicity or immune responses.

Chemotherapy and Immunotherapy Agents

Cancer treatments are a major cause of drug-induced lung injury. Some notable examples include:

Bleomycin: Known to cause pneumonitis and pulmonary fibrosis.
Methotrexate: Can cause hypersensitivity pneumonitis.
Alkylating Agents: Drugs like busulfan can damage lungs with prolonged use.
Tyrosine Kinase Inhibitors and Immune Checkpoint Inhibitors: These newer therapies can cause pneumonitis.
Antibody-Drug Conjugates: Some, such as trastuzumab deruxtecan, carry a risk of interstitial lung disease.

Cardiovascular Medications

Certain heart drugs can have pulmonary side effects:

Amiodarone: This antiarrhythmic is linked to lung toxicity (ALT), which can occur at any dose.
Statins: Rarely associated with drug-induced interstitial lung disease.

Antibiotics and Anti-Inflammatory Drugs

Some drugs in these classes have documented risks:

Nitrofurantoin: Can cause acute and chronic lung injury.
Sulfasalazine: Has been linked to drug-induced lung problems, including noncardiogenic pulmonary edema.
Methotrexate and Anti-TNF Agents: Can lead to various lung injuries, including pneumonitis.

Immunosuppressants

These medications increase the risk of infections, including pneumonia, due to a weakened immune system. This makes patients susceptible to opportunistic infections like Pneumocystis jirovecii pneumonia.

Illicit and Miscellaneous Drugs

Opioids: Prescription opioids can increase pneumonia risk, especially at higher doses, by suppressing immune function.
Cocaine and Heroin: Can cause lung injuries that increase pneumonia risk.
Antipsychotics: Rarely, can increase aspiration pneumonia risk due to Neuroleptic Malignant Syndrome.

Comparison of Key Drug-Induced Lung Injury Mechanisms


Drug Class	Common Examples	Primary Mechanism of Injury	Typical Onset
Chemotherapy (Cytotoxic)	Bleomycin, Methotrexate	Direct cytotoxicity, inflammation, hypersensitivity	Varies; early (methotrexate) or late (busulfan)
Immunotherapy (ICIs)	Pembrolizumab, Nivolumab	Immune system over-activation	Varies; weeks to months after starting
Cardiovascular	Amiodarone	Direct cellular toxicity, immunologic reaction, phospholipid accumulation	Often subacute, months after therapy begins
Antibiotics	Nitrofurantoin, Sulfasalazine	Hypersensitivity reaction	Can be acute (days) or chronic (months/years)
Immunosuppressants	Methotrexate, Steroids	Compromised immune response, hypersensitivity	Varies; increased susceptibility to opportunistic infections
Illicit Drugs	Opioids, Cocaine	Immune suppression, direct tissue damage, aspiration	Can be acute or chronic depending on use

Diagnosis, Treatment, and Risk Factors

Diagnosing drug-induced pneumonia involves a detailed history, imaging, lung function tests, and possibly bronchoscopy to rule out other causes. Discontinuing the medication is the main treatment. Corticosteroids may be used in severe cases.

Risk factors for drug-induced lung injury include:

Older age
Pre-existing lung disease
Higher cumulative drug dose (for some drugs)
Combination therapies
Smoking
Possible genetic factors

Conclusion

While rare, drug-induced lung problems can mimic or increase the risk of pneumonia. Many medications, including those for cancer and heart conditions, are implicated. Accurate diagnosis and discontinuing the offending drug are crucial. Healthcare providers and patients should be vigilant, especially in those with risk factors, and report any new respiratory symptoms.

Frequently Asked Questions

Symptoms often resemble those of infectious pneumonia and can include fever, shortness of breath (dyspnea), and a persistent, dry cough. The onset can be gradual or abrupt, and in some cases, symptoms may not appear for months or years after starting the medication.

Diagnosis is a process of exclusion, starting with a detailed medical history and a high index of suspicion. It involves imaging such as chest X-rays or CT scans, and often requires ruling out other causes, like infections, with blood tests and sometimes bronchoalveolar lavage.

While less common than with powerful prescription drugs, some over-the-counter agents have been linked to lung issues. For example, high doses of salicylates (aspirin) have been associated with an acute respiratory distress syndrome-type reaction.

No. The incidence of drug-induced lung injury is often low and is influenced by a combination of factors, including genetics, dosage, duration of use, and individual patient risk factors. Many individuals tolerate these medications without any pulmonary side effects.

Not necessarily. In acute cases, symptoms often improve or resolve once the offending drug is discontinued, sometimes with the help of corticosteroids. However, some chronic forms, like pulmonary fibrosis, can cause permanent lung damage that may not fully reverse.

Infectious pneumonia is caused by bacteria, viruses, or fungi, while drug-induced pneumonitis is a sterile, inflammatory reaction in the lung to a medication. Both can cause similar symptoms and imaging findings, making differentiation difficult without a high degree of clinical suspicion and diagnostic workup.

You should contact your healthcare provider immediately. It is crucial to inform them of all the medications you are taking, including over-the-counter drugs and supplements. Do not stop any prescribed medication without consulting a doctor first.