Abstract
A 69-year-old woman with diabetes mellitus, hypertension, and chronic thyroiditis was admitted with recurrent attacks of syncope. Since coronary angiography showed total occlusion of right coronary artery, an atrioventricular block or sinus arrest was suspected and the patient was scheduled for implantation of a permanent pacemaker. Insulin treatment and administration of metformin, 500-750 mg/day were started in order to improve her glycemic conditions. About a month later, the patient developed a dry cough, low grade fever, and progressive dyspnea due to severe interstitial pneumonitis and pleural effusion Metformin was discontinued and an infectious etiology was ruled out by cultres, serology and lung biopsy. Prednisolone, 40 mg/day was administered orally and the pneumonitis rapidly improved. After reducing the prednisolone to 10 mg/day, metformin was reintroduced, but the next day the clinical symptome of interstitial pneumonitis reappeared and the metformin was once again discontinued. The patient apparently tested positive in a drug-induced lymphocyte stimulation for metformin. Pulmonary toxicity is a rare adverse effect of metformin and only one case has been previously reported. The clinical course and possible pathogenic mechanisms are discussed.
