Do patients show the same level of adherence with all dry powder inhalers?

Poor adherence with inhaled therapy presents a considerable problem. In the UK, non-adherence is estimated to occur in 10-46% of those prescribed inhaled corticosteroids and may contribute to an estimated 18-48% of asthma deaths. Before dry powder inhalers can be considered interchangeable, it is important to check that adherence is unaffected by any switching of the device dispensed to patients. Numerous studies have shown that adherence with inhaled medication is a multifactorial issue. A number of evidence-based guidelines have concluded that there is no difference in the delivery of treatments from different inhaler devices. However, many studies comparing different devices are designed to show equivalence. It is therefore difficult to determine whether the studies on which the guidelines are based were conducted with treatments already being used at the top of a dose-response curve. Furthermore, studies use selected patient populations who consent to take part and consequently receive regular contact with healthcare professionals, with emphasis on using the correct inhaler technique and on compliance. These studies do not therefore necessarily reflect real life. It is possible that patient preferences or perceptions of differences in efficacy are behind complaints when devices are switched. Patients vary in their preference for different dry powder inhalers, as shown in numerous studies of patient attitudes. There is evidence to indicate that patient claims of differences between inhalers that contain the same molecule from different manufacturers may have an objective basis. Healthcare professionals increasingly recognise the impact of patient attitudes on adherence. Accepting that patients make choices about their therapy is an integral part of achieving the partnership in management recommended by guidelines. The most effective treatment will not achieve disease control if it is not used or if it is used incorrectly. It may be short-sighted to change a device that a patient has chosen to one that is just given without consent, as this may result in poor adherence to therapy with consequent loss of control.