A major depressive episode left untreated may last between 6 and 24 months in 90-95% of cases while the remaining 5-10% could last more than 2 years. Two-thirds of patients are expected to 'respond' to anti-depressant medication and in controlled studies, one-third are expected to respond to placebo. Approximately 15-20% of patients will fail to respond to any anti-depressant trial. It is estimated that approximately 50% of patients will reach remission within the first 6 months and about two-thirds within 2 years of the start of therapy.
The variables predictive of relapse include: (i) multiple prior episodes; (ii) severe episodes; (iii) long-lasting episodes; (iv) episodes with psychotic or bipolar features; and (v) incomplete recovery between two consecutive episodes.
The pharmacological treatment of major depressive episodes can be divided into three phases:
1 An acute phase, which lasts between 6 and 12 weeks, in which the goal is to achieve a complete symptom remission.
2 A continuation phase, which spans the 12th and 52nd weeks, and which aims to prevent the recurrence of a depressive episode. The anti-depressant medication must be maintained at the same dose.
3 A maintenance phase, which aims to maintain the patient in a euthymic state indefinitely. Its duration depends on the number of prior major depressive episodes. As stated above, among patients with primary depression, after a first major depressive episode, the probability of future episodes is about 50%; it increases to 70% after a second episode and is more than 90% after a third episode. The decision to keep the patient on anti-depressant drugs beyond the first 12 months and the duration of a maintenance phase should be decided after consultation with a psychiatrist.
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