To evaluate the persistence rate for estrogen therapy and to identify its determinants.
From the Quebec health insurance database we chose a cohort of 4527 women 35 years and older who received social assistance and were new users of estrogen between January 1989 and December 1997. Incident use was defined by the absence of any dispensed prescription of estrogen in the 3 years before the index date (date of first dispensed prescription). We estimated the cumulative persistence rate of treatment by Kaplan-Meier failure time analysis and identified its determinants with the Cox proportional hazards model.
From the initial cohort, 3395 women (75%) renewed their first dispensed prescription and 905 (20%) continued treatment after 4 years. The determinants measured at the index date and significantly associated with a better persistence rate (relative risk [RR]) were younger than 60 years (RR 1.15, 95% confidence interval [CI] 1.01, 1.30), low dosage (RR 1.49, 95% CI 1.32, 1.70), continuous progestin combination (RR 1.40, 95% CI 1.27, 1.54), and a gynecologist as the first prescribing physician (RR 1.15, 95% CI 1.03, 1.21). Also, coronary heart disease or at least one risk factor for it in the year before the index date was associated with a better persistence rate for estrogen replacement therapy (RR 1.15, 95% CI 1.05, 1.22).
The persistence rate for estrogen therapy is poor, implying that few women take it long enough to benefit from it.