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Objectives: The study aims at investigating the influence of several factors on the probability of receiving one of the two tiotropium formulations (Respimat or Handihaler). Design: Drug utilisation study. Setting: All residents in the Region Umbria, Italy, aged ≥45 years, who received prescriptions of tiotropium during 2011-2012. Participants: Two groups of patients were studied: (1) incident users of the two tiotropium formulations (ie, without tiotropium prescriptions in the previous 6 months); (2) switchers from Handihaler to Respimat. Users of the two formulations were compared with regard to baseline characteristics and medical history. The adjusted OR of receiving Respimat was estimated for several factors. Results: Incident users of the two formulations (4390 participants) had similar characteristics. They were older and with more comorbidities than patients included in randomised control trials (RCTs). Among prevalent users of Handihaler, the probability of switching to Respimat was greater in patients with severe respiratory disease (users of ≥4 respiratory drugs: adjusted OR=4.62; 95% CI 2.46 to 8.69) and among β-blocker users (adjusted OR=1.76; 95% CI 1.13 to 2.75). Age above 75 years and lipid-lowering drug use reduced the probability of switching. A positive association was also found between neurological conditions and the use of Respimat. Conclusions: When starting tiotropium treatment, the choice between the two formulations is weakly affected by comorbidities and chronic obstructive pulmonary disease severity. Instead, these characteristics influence the likelihood of switching from Handihaler to Respimat. Since tiotropium users in clinical practice are more severe than those included in RCTs, further aetiological studies are needed to compare the safety profile of the two formulations in routine care. [ABSTRACT FROM AUTHOR]