Confounding by contraindication in a nationwide cohort study of risk for death in patients taking ibopamine.
BACKGROUND
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.


OBJECTIVE
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.


METHODS
Retrospective cohort study.


METHODS
The Netherlands.


METHODS
1146 patients with congestive heart failure who were prescribed ibopamine at least once and for whom medication history and medical data were available.


METHODS
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).


RESULTS
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.


CONCLUSIONS
The marked inversion of the relative risk estimate can be considered a practical example of confounding by contraindication.
Feenstra
H
H
Department of Internal Medicine, Albert Schweitzer Hospital, Box 444, 3300 AK Dordrecht, the Netherlands.
Grobbee
R E
RE
in't Veld
B A
BA
Stricker
B H
BH
D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D015331:Cohort Studies; D015986:Confounding Factors, Epidemiologic; D000075202:Contraindications; D003846:Deoxyepinephrine / Q000031:analogs & derivatives* / Q000627:therapeutic use; D018491:Dopamine Agonists / Q000627:therapeutic use; D005260:Female; D006333:Heart Failure / Q000188:drug therapy* / Q000401:mortality; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012307:Risk Factors; D011795:Surveys and Questionnaires
D018491:Dopamine Agonists; C023487:ibopamine; D003846:Deoxyepinephrine