Can a drug-induced pulmonary hypersensitivity reaction be dose-dependent? A case with mesalamine.

Mesalamine-induced pulmonary adverse drug reactions (ADRs) in the course of therapy for inflammatory bowel diseases are rare events, having been reported in only 21 cases. This response, resembling hypersensitivity pneumonitis, is considered to be immunologically mediated and thus dose-independent. We report the case of a 70-year-old woman with ulcerative colitis (UC) who developed biopsy-proven interstitial pulmonary disease (lymphocytic alveolitis and mild interstitial pulmonary fibrosis) three months after starting mesalamine therapy. The usual treatment in cases of ADR is cessation of the drug and initiation of corticosteroids. In this case, we continued the mesalamine therapy but halved the dose, and did not add corticosteroids. This approach led to a remission of the pulmonary manifestations without a resurgence of UC symptoms. Based on a review of the literature and our own observation, we challenge the concept that mesalamine-induced pulmonary injury is always due to a hypersensitivity reaction. The evidence suggests that in some cases pulmonary ADR is dose-related; in such instances the most accepted therapy is not necessarily the most appropriate one.