A 38-year-old woman presents to the psychiatry outpatient clinic with a 3-month history of persistent low mood, loss of interest in her job and hobbies, early morning awakening at 4 AM, and significant weight loss of 8 kg. She reports feeling worthless and has recurrent thoughts that her family would be better off without her. She denies any prior psychiatric history or substance use. On mental status examination, she appears psychomotor retarded with restricted affect. What is the most appropriate first-line pharmacological intervention for this patient?

Explanation

## Diagnosis and Management of Major Depressive Disorder **Key Point:** This patient meets DSM-5 criteria for Major Depressive Disorder with melancholic features (early morning awakening, psychomotor retardation, weight loss, anhedonia, guilt/worthlessness) and suicidal ideation. ### First-Line Pharmacotherapy **High-Yield:** SSRIs (selective serotonin reuptake inhibitors) are the gold standard first-line agents for MDD due to efficacy, tolerability, and safety profile. | Agent Class | Examples | Mechanism | First-Line? | |---|---|---|---| | SSRI | Fluoxetine, Sertraline, Escitalopram | Blocks serotonin reuptake | **Yes** | | SNRI | Venlafaxine, Duloxetine | Blocks serotonin + norepinephrine reuptake | Yes (alternative) | | Tricyclic | Amitriptyline, Imipramine | Blocks monoamine reuptake | No (2nd/3rd line) | | Atypical Antipsychotic | Aripiprazole, Quetiapine | D2 antagonism | No (augmentation only) | | Mood Stabilizer | Lithium | Unknown exact mechanism | No (maintenance/augmentation) | | Benzodiazepine | Lorazepam | GABA~A~ agonist | No (adjunct for anxiety/insomnia) | ### Why Fluoxetine 20 mg Daily? 1. **SSRI efficacy:** SSRIs have NNT of 6–7 for response in MDD; equivalent efficacy to other antidepressants but superior tolerability. 2. **Melancholic features:** SSRIs are effective for both neurovegetative symptoms (sleep, appetite) and mood/cognition. 3. **Safety in suicidality:** While SSRIs carry a black-box warning for suicidal ideation in adolescents, they are the safest choice in adults with suicidal thoughts (safer than tricyclics, which are cardiotoxic in overdose). 4. **Dosing:** 20 mg is the standard starting dose; therapeutic response typically appears in 4–6 weeks. **Clinical Pearl:** In patients with suicidal ideation, avoid tricyclic antidepressants (lethal in overdose) and benzodiazepines as monotherapy (disinhibition risk). Always combine antidepressant with psychotherapy and close monitoring. ### Why Not the Other Options? - **Haloperidol:** Antipsychotic; reserved for MDD with psychotic features (this patient has none). Causes extrapyramidal side effects and tardive dyskinesia. - **Lorazepam:** Benzodiazepine; useful for acute anxiety/insomnia but NOT a primary antidepressant. Risk of dependence and disinhibition in suicidal patients. - **Lithium carbonate:** Mood stabilizer; indicated for bipolar disorder maintenance and unipolar MDD augmentation (not monotherapy for acute MDD). Requires therapeutic drug monitoring and has narrow therapeutic index. **Mnemonic:** **SSRI FIRST** — Selective Serotonin Reuptake Inhibitors are First-line in acute MDD, Indicated for Response, Safe in Suicidality, Tolerable, and Recommended by guidelines.