OBJECTIVE: To determine the effect of changing anticholinergic therapy in patients with COPD from ipratropium to tiotropium on pulmonary function. METHODS: We examined records of patients prescribed high-dose ipratropium, who were subsequently converted to tiotropium. Spirometric values were obtained within 2 days of the change in medication and after 56 to 224 days of the switch to tiotropium. RESULTS: 15 subjects were documented to have filled a prescription for ipratropium-containing medications the month prior to the change. Medication compliance over the 6 months prior to the switch in these patients was 72% +/- 31% (mean +/- SD) for ipratropium compared to 87% +/- 14% for tiotropium over the 6-month period after the switch (P = 0.1). FEV(1) improved from 1.12 +/- 0.39 L at baseline to 1.37 +/- 0.49 L after the change to tiotropium (P = 0.01). FVC also improved from 2.45 +/- 0.73 L at baseline to 2.72 +/- 0.69 L after the change (P = 0.04). Maximal voluntary ventilation was also increased from 39.67 +/- 10.7 L/min to 45.13 +/- 15.8 L/min (P = 0.045). CONCLUSIONS: We conclude that replacing high-dose ipratropium with tiotropium therapy significantly improves pulmonary function in a clinical setting.