Pneumonia is an infection or inflammatory illness of the lung. It is often characterized by lung parenchyma (affecting the tissues of the lung) with alveolar inflammation and abnormal filling of the alveoli with fluid (alveoli are microscopic air-filled sacs that absorb oxygen from the air).
Pneumonia is the sixth most common disease leading to death in the U.S. and the most common fatal nosocomial infection (acquired in a hospital). It has many causes, including infection (with viruses, bacteria, and fungi), parasites, chemical or physical injury, or unknown (idiopathic). Because drug-induced pneumonia is not well understood, it is sometimes described as idiopathic.
Symptoms of pneumonia may include:
| Typical | Infectious pneumonia | Less common forms |
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Other symptoms of pneumonia may include:
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The clinical classification of pneumonia has evolved from one based on clinical characteristics to a combined clinical classification scheme, which also attempts to identify the risk factor of the patient at the time the patient is diagnosed.
Under this newer scheme, pneumonia is broadly categorized as community-acquired, hospital-acquired, and healthcare-associated (for patients who are not hospitalized but who recently were in close contact with the healthcare system).
Other types of pneumonia that do not neatly fit into these broader categories include severe acute respiratory syndrome (SARS), bronchiolitis obliterans organizing pneumonia, eosinophilic pneumonia, chemical pneumonia, lipoid pneumonia (actually a sub-category of chemical pneumonia), and aspiration pneumonia (or aspiration pneumonitis).
The types of pneumonia more commonly attributed to drugs include eusinophilic pneumonia, bronchiolitis obliterans organizing pneumonia, desquamative interstitial pneumonia, nonspecific interstitial pneumonia, and cytotoxic pneumonia.
- Eosinophilic pneumonia (EP) – an inflammation of the alveoli resulting from an invasion of the lung by a type of white blood cells called eosinophils. Secondary EP can be induced by parasites, including fungi, exposure to certain types of environmental factors, or medications such as amiodarone (Cordarone) and nitrofurantoin (Furadantin, Macrobid, Macrodantin).
EP can be diagnosed with a chest radiograph, although a high-resolution CT can allow earlier detection and improved characterization of the abnormalities. This is important because drug-induced EP may be identified as the result of the elimination of other causes, and timely discontinuation of the offending drug reduces morbidity and mortality.
- Bronchiolitis obliterans organizing pneumonia (BOOP) – also known as cryptogenic organizing pneumonitis (COP), is caused by inflammation of the small airways of the lungs. Several classes of medications, including antimicrobials, cardiac agents, anticancer agents, and ant-inflammatory agents can cause a BOOP reaction. BOOP is generally reversible by cessation of the offending drug or with corticosteroid therapy.
Drugs that have been associated with BOOP include:
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- Desquamative interstitial pneumonia – a chronic lung inflammation occurring mostly in current and former smokers, can also be induced by drugs such as methotrexate (Rheumatrex), the interferons, and etanercept-D2E7.
- Nonspecific interstitial pneumonia (NSIP)/fibrosis – NSIP is characterized by uniform inflammation of the connective tissue in the lungs and fibrosis, or scarring throughout the lungs. It can be caused by certain medications and treatment usually involves the use of corticosteroids and/or other medications that suppress the immune system. Because the side effects and toxicity of treatment can be serious, pulmonary fibrosis is usually referred to lung specialists.
Drugs that have been associated with NSIP include:
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- Cytotoxic pneumonia – not clinically recognized as such, there are numerous documented instances of pneumonia induced by cytotoxic therapy such as chemotherapy and radiation therapy used to treat cancer patients.