Objective To evaluate the safety of a non-chlorofluorocarbon metered dose salbutamol inhaler.
Design This was a postmarketing surveillance study, conducted under formal guidelines for company sponsored safety assessment of marketed medicines (SAMM). A non-randomised, non-interventional, observational design compared patients prescribed metered doses of salbutamol delivered by inhalers using either hydrofluoroalkane or chlorofluorocarbon as the propellant. Follow up was three months.
Setting 646 general practices throughout the United Kingdom.
Subjects 6614 patients with obstructive airways disease (1667 patient years of exposure).
Main outcome measures Proportions of patients who were: admitted to hospital for respiratory diseases, reported adverse side effects, or withdrew because of adverse affects.
Results There were no significant differences between the hydrofluoroalkane (HFA 134a) and chlorofluorocarbon inhaler groups in relation to the proportions of patients admitted to hospital for respiratory diseases (odds ratio 0.75; 95% confidence interval 0.51 to 1.08) or the proportions who reported adverse events (1.01; 0.88 to 1.17). However, more patients using the hydrofluoroalkane inhaler than the chlorofluorocarbon inhaler withdrew because of adverse events (3.8% and 0.9% respectively).
Conclusion The hydrofluoroalkane inhaler was as safe as the chlorofluorocarbon inhaler when judged by hospital admissions and adverse affects. The study design successfully fulfilled the recommendations of the guidelines. Differences between postmarketing surveillance studies and randomised clinical trials in assessing safety were identified. These may lead to difficulties in the design of postmarketing surveillance studies.
Key messagesCredibility of postmarketing surveillance studies is expected to increase after the introduction of guidelines covering their conduct The study design successfully fulfilled the requirements of these guidelines in terms of the number, rate, and geographical spread of patients recruitedSafety of salbutamol inhalers using hydrofluoroalkane and chlorofluorocarbon as propellants is similarImportant differences in study design/conduct and outcome between a postmarketing surveillance study and a randomised clinical trial merit further consideration.