Effects of financially-induced inhaler switching on the risk of an acute exacerbation in patients with asthma or chronic obstructive pulmonary disease (COPD): a self-controlled case series

Application Number
Lay Summary

Asthma and COPD are common chronic respiratory conditions affecting over 6 million people in the UK. Most people with COPD and asthma require regular inhaled medication as the mainstay of their treatment. Inhalers used for asthma and COPD make up some of the most expensive drug costs for the NHS; three of the top five most expensive NHS drugs are inhalers. There is a drive towards providing value care and therefore, when cheaper inhalers (usually generic, non-trade name, inhalers) come onto the market there is often an implementation of policies to change patient's medication. Sometimes cheaper preparations contain the same active substance but other components differ, including the inhaler device which may require a different technique to use. The effect on a medically stable asthma or COPD patient's control is completely unclear; however, anecdotal patient reports and small studies suggest this policy may increase the risk of acute exacerbations (sudden worsening of respiratory symptoms). This study will measure the risk of acute exacerbations after financial-induced inhaler switching in clinically stable asthma and COPD patients; the finding of either an increase or null effects on the risk of exacerbations will provide valuable information for healthcare workers, patients and policy makers.

Technical Summary

We will use CPRD linked with HES and ONS to conduct a self-controlled case series (SCCS) to measure the difference in the risk of an acute exacerbation, in patients with asthma or COPD, shortly after a switch of their usual inhaler instigated at their GP practice for technical reasons, compared to times when a switch has not been instigated. SCCS is suited to this current research question as there are precise timings available of a transient exposures (inhaler switch) and a non-recurrent event (first acute exacerbation during follow-up). The incidence rate ratio of acute exacerbations will be estimated comparing exposed periods (3 months following the inhaler switch) to unexposed periods (11 months before inhaler switch and 9 months after) in a conditional Poisson regression model. SCCS implicitly controls for time invariant confounders but time varying confounders will be controlled for in the analysis. We will investigate potential effect modification by disease type, severity of disease, and inhaler switch type by stratified analysis.

Health Outcomes to be Measured

Incident asthma exacerbations; Incident COPD exacerbations.


Jennifer Quint - Chief Investigator - Imperial College London
Chloe Bloom - Corresponding Applicant - Imperial College London
Ian Douglas - Collaborator - London School of Hygiene & Tropical Medicine ( LSHTM )


HES Accident and Emergency;HES Admitted Patient Care;ONS Death Registration Data;Practice Level Index of Multiple Deprivation