3 broad groups of drug reactions can be recognized in the lung

Toxic or dose related: there is diffuse alveolar damage in the early or organizing phase. Later on interstitial scarring and honeycombing may be seen
Idiosyncratic or allergic reactions: these include bronchiolitis obliterans, BOOP, nonspecific interstitial inflammation, granulamatous interstitial pneumonia, eosinphilic pneumonia, UIP, DIP, LIP vasculitis and mixtures of above
Miscellaneous reactions, a few of which have specific features: these include pulmonary edema, alveolar hemorrhage, histiocytic infiltrates and phospholipidosis (amiodarone), metastatic calcification, asthma, foreign body giant cell reaction (IV talcosis), pulmonary hypertension, pleuritis and veno-occlusive disease
- Busulphan: bizarre hyperchromatic Type II pneumocytes
- Methotrexate: small granulomas are seen in one-third to one-half of all cases of methotrexate pneumonitis
- Amiodarone toxicity: Histiocytes within airspaces contain cytoplasmic vacuoles which are characteristic but not diagnostic