General Practice

Postmarketing surveillance study of a non-chlorofluorocarbon inhaler according to the safety assessment of marketed medicines guidelines

J G Ayres, professor, ^a C D Frost, lecturer, ^b W F Holmes, general practitioner, ^c D R R Williams, professor, ^d S M Ward, clinical research specialist. ^e

^a Department of Respiratory Medicine, Birmingham Heartlands Hospital, Birmingham, B9 5SS, ^b Medical Statistics Unit, London School of Hygiene and Tropical Medicine, London WC1 7HT, ^c Sherrington Park Medical Practice, Nottingham NG5 2EJ, ^d Division of Public Health, Nuffield Institute for Health, Leeds LS2 9PL, ^e 3M Health Care, Loughborough LE1 11EP

Correspondence to: Professor Ayres

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.