A 28-year-old woman presents to the psychiatry clinic with a 3-year history of intrusive thoughts that her hands are contaminated with harmful bacteria despite frequent handwashing. She washes her hands 15–20 times daily, sometimes until they bleed. She recognizes these thoughts are irrational but feels unable to resist the urge to wash. Her handwashing rituals consume 2–3 hours per day and significantly impair her work and social functioning. She denies depression, hallucinations, or suicidal ideation. What is the most appropriate first-line pharmacological intervention?

Explanation

## Diagnosis and Pharmacotherapy of OCD **Key Point:** Selective serotonin reuptake inhibitors (SSRIs) are the first-line pharmacological treatment for obsessive-compulsive disorder, with fluoxetine, sertraline, paroxetine, and fluvoxamine all FDA-approved and evidence-based. ### Clinical Presentation Recognition The patient exhibits: - **Obsessions:** intrusive, unwanted thoughts about contamination - **Compulsions:** repetitive handwashing rituals performed to reduce anxiety - **Insight:** she recognizes the irrationality of her thoughts (good insight) - **Functional impairment:** significant time spent on rituals (>1 hour/day) and occupational/social dysfunction These features meet DSM-5 criteria for OCD. ### SSRI Dosing in OCD | SSRI | First-Line Dose | Therapeutic Dose for OCD | Notes | |------|-----------------|--------------------------|-------| | Fluoxetine | 20 mg/day | 40–80 mg/day | Longer half-life; slower titration | | Sertraline | 25–50 mg/day | 50–200 mg/day | Shorter half-life; faster titration | | Paroxetine | 10–20 mg/day | 40–60 mg/day | Higher discontinuation syndrome risk | | Fluvoxamine | 50 mg/day | 100–300 mg/day | Shortest half-life; multiple dosing | **High-Yield:** OCD typically requires **higher SSRI doses and longer duration** (8–12 weeks) compared to depression (4–6 weeks). Fluoxetine 40–80 mg/day is standard. ### Why SSRIs Work in OCD SSRIs enhance serotonergic transmission in the orbitofrontal cortex and anterior cingulate cortex, which are hyperactive in OCD. This reduces the salience of obsessions and facilitates cognitive-behavioral therapy (CBT). **Clinical Pearl:** Augmentation with low-dose antipsychotics (risperidone, aripiprazole) is considered if SSRI monotherapy fails after 8–12 weeks at therapeutic dose. ### Treatment Algorithm ```mermaid flowchart TD A[OCD Diagnosis Confirmed]:::outcome --> B[First-line: SSRI]:::action B --> C[Fluoxetine 40-80 mg/day<br/>or Sertraline 50-200 mg/day]:::action C --> D{Response after<br/>8-12 weeks?}:::decision D -->|Yes| E[Continue SSRI +/- CBT]:::action D -->|No| F[Increase SSRI dose<br/>or switch SSRI]:::action F --> G{Response?}:::decision G -->|No| H[Add antipsychotic<br/>risperidone/aripiprazole]:::action G -->|Yes| E ``` [cite:Harrison 21e Ch 476]