Case 1 was a 59-year-old female who had been taking distigmine bromide 20 mg/day for 2 years. She had concurrently developed pneumonia and was admitted to the hospital. Her pupil diameter was 1.0 mm, serum ChE value was decreased at 25 IU/L. Case 2 was a 72-year-old male who had been taking distigmine bromide 15 mg/day for 8 months. He was transported to the hospital with a chief complaint of dyspnea. His pupil diameter was 2.0 mm, serum ChE value was decreased at 75 IU/L, and he had concurrent pyothorax. Case 3 was a 74-year-old male who had been taking distigmine bromide 10 mg/day for 4 years. He was transported to the hospital with a chief complaint of disturbance of consciousness. His pupil diameter was 2.0 mm, and serum ChE value was decreased at 55 IU/L. He had concurrent aspiration pneumonia. In Case 1, the distigmine bromide concentration was elevated at 13.2 ng/mL at admission. However, it decreased from the following day. The two other patients had low concentrations of distigmine bromide. In all patients, ChE levels recovered after discontinuing distigmine bromide, and respiratory conditions also improved. Distigmine bromide was no longer detected in blood before ChE levels recovered.