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Confounding by indication and channeling over time: the risks of beta 2-agonists
1Department of Epidemiology and Biostatistics, McGill Pharmacoepidemiology Research Unit, McGill University, Montreal, Canada.
American Journal of Epidemiology
|December 15, 1996
Summary
The Saskatchewan Asthma Epidemiologic Project (SAEP) found potential bias in comparing inhaled fenoterol and salbutamol due to doctors prescribing fenoterol to more severe asthma cases. Long-term medication data is crucial for accurate asthma research.
Area of Science:
- Pharmacovigilance
- Epidemiology
- Respiratory Medicine
Background:
- Previous studies suggested differing risks for inhaled fenoterol and salbutamol in asthma patients.
- The potential for "confounding by indication" in these comparisons was not fully explored.
Purpose of the Study:
- To investigate whether inhaled fenoterol was preferentially prescribed to more severely ill asthma patients.
- To assess if asthma severity influenced the initial choice or switching patterns between fenoterol and salbutamol.
Main Methods:
- Analysis of a 7-year follow-up cohort of 12,301 asthma patients from Saskatchewan Health databases.
- Examination of prescribing patterns for initial prescriptions and medication switches between fenoterol and salbutamol.
- Investigation of the association between asthma severity, disease control, and the use of these two inhaled beta-2 agonists.
Main Results:
- The initial prescription choice between fenoterol and salbutamol was not linked to asthma severity or control.
- Fenoterol was preferentially prescribed to patients already using salbutamol who exhibited worsening asthma or poor disease control.
- Switching from inhaled fenoterol to salbutamol showed minimal association with asthma severity.
Conclusions:
- The comparison of fenoterol and salbutamol risks in the SAEP study may have been confounded by indication.
- This highlights the necessity of long-term medication use data to prevent indication bias in epidemiological studies.