While pneumonitis generally refers to inflammation of lung tissue, pneumonia is a type of pneumonitis usually caused by infection. And while drug-induced pneumonitis is generally considered as distinct from pneumonitis triggered by inhaled antigens (substances that when introduced into the body stimulate the production of antibodies), hypersensitivity pneumonitis (HP), which is caused by inhaling a foreign substance, can also be caused by certain drugs. This can lead to confusion.
HP, in fact, which is also known as extrinsic allergic alveolitis, is actually a group of disorders that can lead to recurrent pneumonitis, pulmonary fibrosis, or emphysema. The disorders are classically considered occupational illnesses, and most are named after the associated occupation. Some of these illnesses, for instance, include farmer’s lung, bird breeder’s lung, and woodworker’s lung.
HP induced by drugs is often treated with steroids or on dechallenge (withdrawal of the offending drug) and the prognosis is favorable. Drugs that have been associated with HP include:
Methodraxate, gold salts, and amiodarone have also been implicated in other types of pneumonitis. Rarer causes of drug-induced pneumonitis include:
- Nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin and ibuprofen (Advil, Motrin)
- Anticonvulsants such as carbamazepine (Tegretol, Biston, Calepsin) and phenytoin
- Antibiotics such as dapsone
- Sulfonamides such as sulfasalazine (Azulfidine) and sulfadoxine
- Immunosuppressants such as penicillamine (Cuprimine, Depen) and cyclophosphamide (Cytoxan, Neosar)
- Cytotoxic agents bleomycin (Blenoxane), chlorambucil (Leukeran), mitomycin, and vinblastine
Types of pneumonitis other than HP that are known to have been drug-induced include:
- Mild eosinophilic pneumonitis
- Acute eosinophilic pneumonitis
- Amiodarone pneumonitis
- Aspiration pneumonitis
- Radiation pneumonitis (secondarily, as the result of complications from other drug-induced diseases)