Explaining the variation between practices in the duration of new antidepressant treatment: a database cohort study in primary care

Background Practices vary in the duration of newly initiated antidepressant treatment, even after adjusting for patient characteristics. It was hypothesised that this may be because of differences between practices in demographic (practice deprivation and antidepressant prescribing rates), organisational (practice size and proportion of female GPs), and clinical factors (proportion of new episodes of depression coded). Aim To examine the effect of practice characteristics on the duration of new selective serotonin reuptake inhibitor antidepressant treatment in primary care. Design and setting Database cohort study of 28 027 patients from 237 GP practices in Scotland. Method Prescription data were used to estimate duration of treatment for individual patients beyond three time points: 30, 90, and 180 days. Data at patient and practice level were analysed by multilevel logistic regression to quantify the variation between practices. Results The mean rate of diagnostic coding for depression in patients beginning a course of treatment was 29% (range 0–80%). Practice-level deprivation and rate of new antidepressant prescribing were not associated with duration of treatment. The practice level factor most strongly associated with duration of treatment at practice level was the proportion of patients coded as having depression: odds ratio for continuing beyond 30 days was 1.54 (95% confidence interval [CI] = 1.22 to 1.94); beyond 90 days, 1.37 (95% CI = 1.09 to 1.71); and beyond 180 days 1.41 (95% CI = 1.10 to 1.82). Conclusion Encouraging coding and structured follow-up at the onset of treatment of depression is likely to reduce early discontinuation of antidepressant treatment and improve outcomes.