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Prescriptions for Estrogen Replacement Therapy in Ontario Before and After Publication of the Women's Health Initiative Study
To the Editor: Landmark clinical trials can influence prescribing behavior.1-3 We examined patterns of prescriptions for estrogen replacement therapy (ERT) before and after publication of the Women's Health Initiative (WHI) study4 on July 17, 2002. We also examined trends around the publication of the Heart and Estrogen/progestin Replacement Study (HERS)5 in 1998.
Methods
We studied claims for ERT to Ontario's universal Drug Benefit program for seniors (ODB), which tracks medication use by all 1.3 million residents of Ontario older than 65 years. We studied claims submitted between January 1, 1992, and December 31, 2002. For each quarter of each year, we determined the proportion of women older than 65 years who filled a prescription for ERT in Ontario. The number of women older than 65 years in each year was obtained from Statistics Canada. We also determined the number of prescriptions filled by women who had not filled a prescription for ERT in the previous 365 days to determine the number of incident users of ERT in each quarter.
Time series analysis using exponential smoothing models was used to model the quarterly data from the first quarter of 1992 (1993 for new users data) to the second quarter of 2002. In order to determine the impact of the publication of the WHI trial on use of ERT, projections and 95% confidence intervals were obtained for the third and fourth quarters of 2002.
Results
The prevalence of use of ERT among elderly women increased steadily until 1999, at which point it reached a plateau (Figure 1). Following the publication of the WHI trial, prescriptions for ERT decreased dramatically, with use being approximately 32% lower in the last quarter of 2002 than in the same quarter a year earlier. The actual prevalence of use in the last 2 quarters of 2002 was significantly lower than that predicted by the model (P<.001).
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Figure. Prevalence and Incidence of Use of ERT in Elderly Women
ERT indicates estrogen replacement therapy; HERS, Heart and Estrogen/progestin Replacement Study; WHI, Women's Health Initiative.
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The number of new users of ERT increased steadily until the publication of the HERS study, after which it began to decrease. However, the decline in the number of new users accelerated in the third quarter of 2002, with the number of new users in this quarter being significantly less than that predicted by the model (P = .02).
Comment
In the 2 quarters following the publication of the WHI study, we found a large decline in both the prevalence of ERT use among elderly women and in the number of incident users of ERT.
Although our study was limited to women older than 65 years, our data include all elderly women in Ontario. This limitation is also balanced by the fact that women aged 65 years or older are postmenopausal and thus unlikely to be taking ERT for symptom relief. Unfortunately, we were unable to determine whether the decline in use of ERT was physician- or patient-initiated. Nonetheless, we found that a well-publicized large clinical study may be associated with changes in medication prescription and use.
AUTHOR INFORMATION
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Funding/Support: The Institute for Clinical Evaluative Sciences is funded in part by an operating grant from the Ontario Ministry of Health and Long-term Care.
Peter C. Austin, PhD;
Muhammad M. Mamdani, PharmD, MA, MPH
Institute for Clinical Evaluative Sciences
Toronto, Ontario
Karen Tu, MD, CCFP;
Liisa Jaakkimainen, MD, MSc, CCFP
Department of Family and Community Medicine
University of Toronto
Toronto, Ontario
1. Lamas GA, Pfeffer MA, Hamm P, Wertheimer J, Rouleau JL, Braunwald E, SAVE Investigators. Do the results of randomized clinical trials of cardiovascular drugs influence medical practice? N Engl J Med. 1992;327:241-247.
ABSTRACT
2. Mamdani MM, Tu JV. Did the major clinical trials of statins affect prescribing behaviour? CMAJ. 2001;164:1695-1696.
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3. Jackevicius CA, Anderson GM, Leiter L, Tu JV. Use of statins in patients after acute myocardial infarction. Arch Intern Med. 2001;161:183-188.
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4. Writing Group for the Women's Health Initiative Investigators. Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results from the Women's Health Initiative randomized controlled trial. JAMA. 2002;288:321-333.
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5. Hulley S, Grady D, Bush T, et al, Heart and Estrogen/progestin Replacement Study (HERS) Research Group. Randomized trial of estrogen plus progestin for secondary prevention of coronary heart disease in postmenopausal women. JAMA. 1998;280:605-613.
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Letters Section Editor: Stephen J. Lurie, MD, PhD, Senior Editor.
JAMA. 2003;289:3241-3242.
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