Hans Feenstra, MD, PhD; Rick E. Grobbee, MD, PhD; Bas A. in't Veld, MD, PhD; Bruno H.Ch. Stricker, MB, PhD
Acknowledgment: The authors thank the general practitioners and pharmacists in the Netherlands who contributed information.
Grant Support: By the Inspectorate for Health Care of the Dutch Ministry for Health, Welfare, and Sports.
Requests for Single Reprints: Bruno H.Ch. Stricker, MB, PhD, Department of Epidemiology & Biostatistics, Erasmus University Medical School, Box 1738, 3000 DR Rotterdam, the Netherlands.
Current Author Addresses: Dr. Feenstra: Department of Internal Medicine, Albert Schweitzer Hospital, Box 444, 3300 AK Dordrecht, the Netherlands.
Dr. Grobbee: Julius Center for Patient Oriented Research, Box 85500, 3508 GA Utrecht, the Netherlands.
Dr. in't Veld: Department of Anesthesiology, Academic Medical Centre, Box 9600, 2300 RC Leiden, the Netherlands.
Dr. Stricker: Department of Epidemiology & Biostatistics, Erasmus University Medical School, Box 1738, 3000 DR Rotterdam, the Netherlands.
Author Contributions: Conception and design: H. Feenstra, R.E. Grobbee, B.A. in't Veld, B.H.Ch. Stricker.
Analysis and interpretation of the data: H. Feenstra, R.E. Grobbee, B.A. in't Veld, B.H.Ch. Stricker.
Drafting of the article: H. Feenstra, R.E. Grobbee, B.A. in't Veld, B.H.Ch. Stricker.
Critical revision of the article for important intellectual content: H. Feenstra, R.E. Grobbee, B.H.Ch. Stricker.
Final approval of the article: H. Feenstra, R.E. Grobbee, B.A. in't Veld, B.H.Ch. Stricker.
Statistical expertise: R.E. Grobbee, B.H.Ch. Stricker.
Obtaining of funding: B.H.Ch. Stricker.
Collection and assembly of data: H. Feenstra, B.A. in't Veld, B.H.Ch. Stricker.
Outcomes may differ in treated and untreated patients because of a contraindication for treatment in the latter that is independently associated with the outcome of interest.
To evaluate the effects of confounding by contraindication on risk factors for death in patients taking ibopamine after its use was restricted in early September 1995.
Retrospective cohort study.
1146 patients with congestive heart failure who were prescribed ibopamine at least once and for whom medication history and medical data were available.
Cardiovascular risk factors, clinical characteristics, and medication use. Each patient was assigned an index date (the date of death, or a random date for patients still alive at the end of the study).
In univariate analyses comparing patients with an index date before and those with an index date after 8 September 1995, the relative risk for death associated with current use of ibopamine was 3.02 (95% CI, 2.12 to 4.30) compared with 0.71 (CI, 0.53 to 0.96), respectively. In multivariate analyses, the risk for death was 2.62 (CI, 1.76 to 3.90) and 0.93 (CI, 0.84 to 1.02), respectively.
The marked inversion of the relative risk estimate can be considered a practical example of confounding by contraindication.
Feenstra H, Grobbee RE, in't Veld BA, Stricker BH. Confounding by Contraindication in a Nationwide Cohort Study of Risk for Death in Patients Taking Ibopamine. Ann Intern Med. ;134:569–572. doi: 10.7326/0003-4819-134-7-200104030-00010
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Published: Ann Intern Med. 2001;134(7):569-572.
Cardiology, Coronary Risk Factors, Heart Failure, Prevention/Screening.
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