Early Improvement in Individual Symptoms and Response to Antidepressants in Patients With Major Depressive Disorder

Major depressive disorder (MDD) affects around 7% of the population yearly. Although effective treatments are available, only around half of all patients participating in clinical trials respond to 6 to 12 weeks of antidepressant treatment. Given these high failure rates, the ability to predict as early as possible whether a patient is (un)likely to respond would be of great value, as it would enable physicians to change treatment strategies faster. Early improvement has consistently been found to be a strong predictor of later response. However, misclassification is still quite common, with perhaps a third of those who do not show early improvement going on to respond. Conversely, a substantial proportion of those who do show early improvement do not go on to respond. One possibility for improving the predictive power of early improvement is to examine individual symptoms, rather than the total score on a depression rating scale. Some items, for example, could reflect antidepressant side effects (e.g. gastrointestinal symptoms) and may not be very predictive. The proposed project aims to examine the relationship between early improvement in individual symptoms and response to antidepressants in a very large patient sample. This large sample size makes it possible to use more rigorous methods than previous studies, such as the use of cross-validation to confirm the findings. It also makes it possible to examine a large set of predictors, including possible interactions among early-improving symptoms and between symptoms and demographic factors like age and gender. The added value of individual symptoms over and above using the total symptom score alone will also be examined, as well as possible differences between different antidepressant classes. The project will use penalized (lasso) regression, which is well-suited to analyzing data with a large number of (potentially highly correlated) predictors. In the primary analysis, response after 6 weeks of treatment will be predicted. In secondary analyses, remission at week 6 and response and remission at week 12 will also be predicted.