 |
|
Changes in Prescribing Patterns Following Publication of the ALLHAT Trial
To the Editor: Antihypertensive agents are among the most commonly prescribed medications for elderly persons in North America.1 The Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT), published on December 18, 2002, concluded that thiazide-type diuretics should be the first-step antihypertensive therapy, compared with either calcium channel blockers (CCBs) or angiotensin-converting enzyme (ACE) inhibitors.2 We examined trends in incident use of antihypertensive agents following publication of the ALLHAT trial.
Methods
We studied claims for antihypertensive agents that were submitted to the Ontario Drug Benefit (ODB) program between January 1, 1992, and April 30, 2003. The ODB program tracks prescriptions dispensed to all 1.3 million residents of Ontario older than 65 years. We examined claims for the following classes of antihypertensive agents: thiazide-type diuretics, CCBs,  -blockers, and ACE inhibitors or angiotensin receptor blockers. For each month of each year, we determined the number of prescriptions filled by patients who had not filled a prescription for any antihypertensive agent in the previous 365 days to determine the number of incident users of antihypertensive agents. In order to determine relative market share, we determined the proportion of new prescriptions that belonged to each of the 4 classes, for each of the study months.
Time series analysis using exponential smoothing models was used to model the monthly data from January 1993 to December 2002. In order to determine the impact of the publication of the ALLHAT trial on the use of each class of antihypertensive agent, projections and 95% confidence intervals were obtained for each of the first 4 months of 2003.
Results
The monthly relative market share of incident use of each class of antihypertensive agent is described in Figure 1. For increased resolution, we illustrate only the time trends from July 1999 to April 2003. In November, the month prior to the publication of the trial, the relative market shares of thiazide-type diuretics and ACE inhibitors /ARBs were 16.0% and 44.3%, respectively. However, in January, the month following the trial's publication, the relative market shares were 26.5% and 35.4%, respectively. In the 4 months following publication of the ALLHAT trial, the relative market share of thiazide-type diuretics increased significantly compared with that predicted by the time-series model (P<.001 for each month). The relative market share of ACE inhibitors and ARBs decreased significantly compared with that predicted by the time-series model in each of the 4 months following the trial (P<.001 for each month). The relative market share of -blockers was not affected by the publication of the trial (P .47 for each of the 4 months). Finally, the relative market share of CCBs decreased marginally, but statistically significantly, compared with the predicted market share in the first 2 months following the report of the trial (15.1% vs 17.3% [P = .008] and 14.0% vs 16.5% [P = .009], respectively), but resumed to projected levels in March and April (15.4% vs 16.2% [P = .43] and 15.0% vs 15.6% [P = .60], respectively).
|
|
|
|
Figure. Relative Market Share of Antihypertensive Agents
ALLHAT indicates Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial.
|
|
|
Comment
For the 4 months following the publication of the ALLHAT trial, we found a statistically significant increase in the relative market share of thiazide-type diuretics and a statistically significant decrease in the relative market share of ACE inhibitors and ARBs.
There are several instances in the literature in which large, well-publicized randomized trials had a significant impact upon prescribing patterns.3-4 However, this is the first trial of which we are aware that has significantly influenced prescribing behavior by demonstrating that a generically available, less expensive drug may be more clinically favorable than more expensive brand-name drugs. This suggests that many physicians may be influenced by clinical evidence irrespective of the cost or brand-name status of a drug.
There are several limitations of our study. First, we were unable to determine the indication for which each antihypertensive medication was prescribed. Several agents have indications for use other than hypertension. For instance, -blockers and ACE inhibitors are used in the treatment of acute myocardial infarction and congestive heart failure. However, there is no reason to expect the relative number of patients who are not hypertensive to change dramatically from month to month. Furthermore, we would not expect detection of hypertension to improve substantially immediately following the publication of the trial. Second, our data were limited to individuals older than 65 years, and thus may not be representative of all patients with hypertension. However, this is balanced by the fact that the data are population-based, providing coverage for all elderly residents in Ontario, the most populous province in Canada. Third, it is conceivable that future market share may revert to historical patterns.
In summary, we found that a large, well-publicized randomized trial resulted in a significant shift of market share between different classes of antihypertensive agents. Thiazide-type diuretics, which are low-cost agents available in generic format, gained prescribing market share at the expense of ACE inhibitors and ARBs, which are newer, more expensive agents.
Funding/Support: The Institute for Clinical Evaluative Sciences is supported in part by a grant from the Ontario Ministry of Health and Long Term Care. Dr Austin is supported in part by a New Investigator award from the Institute of Health Services and Policy Research of the Canadian Institutes of Health Research.
Disclaimer: The opinions, results and conclusions herein are those of the authors and no endorsement by the Ministry of Health and Long-Term Care or by the Institute for Clinical Evaluative Sciences is intended or should be inferred.
Peter C. Austin, PhD;
Muhammad M. Mamdani, PharmD, MA, MPH;
Karen Tu, MD, MSc, CCFP;
Merrick Zwarenstein, MB, BCh, MSc(Med), MSc
Institute for Clinical Evaluative Sciences
Toronto, Ontario
1. Kaufman DW, Kelly JP, Rosenberg L, Anderson TE, Mitchell AA. Recent patterns of medication use in the ambulatory adult population of the United States. JAMA. 2002;287:337-344.
FREE FULL TEXT
2. ALLHAT Officers and Coordinators for the ALLHAT Collaborative Research Group. Major outcomes in high-risk hypertensive patients randomized to angiotensin-converting enzyme inhibitor or calcium channel blocker vs diuretic: the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT). JAMA. 2002;288:2981-2997. [published correction appears in JAMA. 2003;289:178].
FREE FULL TEXT
3. Austin PC, Mamdani MM, Tu K, Jaakkimainen L. Trends in use of estrogen replacement therapy in Ontario, Canada following publication of the Women's Health Initiative Study. JAMA. 2003;289:3241-3242.
FREE FULL TEXT
4. Tu K, Mamdani MM, Jacka RM, Forde NJ, Rothwell DM, Tu JV. The striking effect of the Heart Outcomes Prevention Evaluation (HOPE) on ramipril prescribing in Ontario. CMAJ. 2003;168:553-557.
FREE FULL TEXT
Letters Section Editor: Stephen J. Lurie, MD, PhD, Senior Editor.
JAMA. 2004;291:44-45.
RELATED ARTICLE
The Complex World of Prescribing Behavior
C. David Naylor
JAMA. 2004;291(1):104-106.
EXTRACT
| FULL TEXT
|
