Factors associated with duration of new antidepressant treatment: analysis of a large primary care database

It is not known how much the duration of newly prescribed antidepressant treatment is influenced by patient characteristics or practice variation. To describe the relationship between patient characteristics and the duration of new antidepressant treatment by general practices. Large primary care database cohort study of all patients with a newly initiated course of eligible antidepressant treatment during 1 year, from a database of 237 Scottish practices. Detailed prescription data were used to estimate the duration of new antidepressant treatment for each patient. Cox proportional hazards regression was used to estimate the influence of patient characteristics on continuation of treatment and, by multilevel modelling, the variation between practices. A total of 28 027 (2.2%) patients commenced antidepressant treatment during the year; 75% continued beyond 30 days, 56% beyond 90 days, and 40% beyond 180 days. Treatment was less likely to be continued in patients from areas of high socioeconomic deprivation: hazard ratio 1.22 (95% confidence interval [CI] = 1.16 to 1.29); in patients under 35 years, 1.33 (95% CI = 1.28 to 1.37); and in those for whom the GP recorded no relevant diagnostic code, 1.16 (95% CI = 1.13 to 1.18). Models accounted for between 2.2% and 3.9% of the variation in treatment duration. Patient demographic characteristics account for relatively little variation in the duration of new antidepressant treatment, though treatment was shorter in younger patients and those with greater socioeconomic deprivation. There is variation in treatment duration between practices and according to whether patients have a depression diagnosis coded in their records.