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

Background It is not known howmuch the duration of newly prescribed antidepressant treatment is influenced by patient characteristics or practice variation. Aim To describe the relationship between patient characteristics and the duration of new antidepressant treatment by general practices. Design and setting Large primary care database cohort study of all patients with a newly initiated course of eligible antidepressant treatment during 1 year, froma database of 237 Scottish practices. Method 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, bymultilevelmodelling, the variation between practices. Results 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 fromareas 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 whomthe 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. Conclusion 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.