Erlotinib-induced acute interstitial lung disease associated with extreme elevation of the plasma concentration in an elderly non-small-cell lung cancer patient.

We herein describe a case of drug-induced interstitial lung disease (ILD) following treatment with erlotinib. The plasma trough concentration of erlotinib at the time of the ILD diagnosis was extremely elevated compared with the plasma maximum concentration on day 1. We hypothesized that this phenomenon was associated with the pharmacodynamic interaction with a concomitant drug. The present case indicates that erlotinib-induced ILD was associated with a high plasma concentration of erlotinib. Oncologists should be aware of the possibility of ILD induced by erlotinib, especially for patients with co-morbidities.