The treatment period will be 6 weeks during which all patients will make 7 study visits and be in contact with study nurse or physician by phone at 4 occasions. The first visit is a screening visit followed by a baseline visit for inclusion and start of treatment with OSU6162 or placebo.~Those responding to treatment will be offered to participate in the extension phase of the study for an additional 4 weeks during which the patients will make 3 study visits and take 3 telephone interviews.~Before inclusion in the study, all patients will be informed both verbally and in writing about its purpose, its procedures, and possible risks associated with participation. Before any study-specific procedures take place, written informed consent will be obtained.~For participation in the extension phase, four factors must be fulfilled: 1. The patient must regard himself/herself as clearly improved and be willing to continue. 2. The investigator must assess the patient as clearly improved. 3. The patient must display at least 50% reduction on HDRS6 as compared to baseline. 4. The patient must have signed a new informed consent.~While assessment of the efficacy and safety of OSU6162 is the main objective of this study, possible differences between the two treatment groups with respect to a number of biomarkers in serum will also be explored.~The primary evaluation of efficacy will be undertaken at the endpoint of the 6-week trial. All analyses will however be repeated also at the endpoint of the 4-week extension phase for subjects participating in this part of the study.~Data will be analysed using mixed models for repeated measurement which means that the model includes data from all depression ratings from baseline to endpoint; this method, which is usually recommended to be used in depression trials by the authorities, is considered to handle data loss due to patients leaving a study prematurely in a better way than imputation methods such as the last observation carried forward (LOCF) technique.
This is a randomised, placebo-controlled, parallel-group trial comparing OSU6162 at flexible dosage with placebo as add-on to treatment with an SSRI/SNRI in patients with depression that have not responded to treatment with an SSRI/SNRI per se for at least 6 weeks. The study will last for 6 weeks, after which those not having responded will leave the trial and those having responded will be offered to continue treatment without unblinding for another 4 weeks.~While assessment of the efficacy and safety of OSU6162 is the main objective of this study, possible differences between the two treatment groups with respect to a number of biomarkers in serum will also be explored.