Fluoxetine

# Fluoxetine ## Overview Fluoxetine is a selective serotonin reuptake inhibitor (SSRI) approved for major depressive disorder, obsessive-compulsive disorder, bulimia nervosa, and panic disorder. It has a long half-life (4–6 days; active metabolite norfluoxetine 4–16 days), requiring 4–5 weeks to reach steady state. ## Primary Indications - Major depressive disorder (MDD) - Obsessive-compulsive disorder (OCD) - Bulimia nervosa - Panic disorder (with or without agoraphobia) - Premenstrual dysphoric disorder (PMDD; lower dose, intermittent or continuous) ## Adult Dosing - **MDD/OCD:** Start 20 mg once daily in the morning; may increase after several weeks by 20 mg/day increments. Max 80 mg/day. - **Bulimia nervosa:** 60 mg once daily (fixed dose). - **Panic disorder:** Start 10 mg once daily; after 1 week increase to 20 mg. Max 60 mg/day. - **PMDD (continuous):** 20 mg once daily; max 80 mg/day. - **PMDD (intermittent):** 20 mg once daily starting 14 days before menses through first full day of menses; may increase to 60 mg/day. ## Pediatric Dosing - **MDD (8–17 years):** Start 10–20 mg once daily. After 1 week, may increase to 20 mg/day. For lower-weight children, start 10 mg/day. Max 60 mg/day (lower weights: 20–40 mg/day). - **OCD (7–17 years):** Start 10 mg once daily; after 2 weeks, increase to 20 mg/day. Range 20–60 mg/day. Max 80 mg/day (lower weights: 60 mg/day). ## Dose Adjustments - **Hepatic impairment:** Reduce dose by 50% or decrease frequency (e.g., 20 mg every other day). - **Renal impairment (eGFR <30):** No specific guidelines; use caution and consider lower starting dose. - **Elderly:** Start 10 mg once daily; increase cautiously. ## Contraindications - Hypersensitivity to fluoxetine or any excipient. - Concomitant use with MAOIs (including linezolid or IV methylene blue) — risk of serotonin syndrome. Allow 5 weeks after stopping fluoxetine before starting an MAOI. - Concomitant use with pimozide or thioridazine (QT prolongation risk). ## Adverse Effects - Nausea, diarrhea, anorexia, weight loss, insomnia, anxiety, nervousness, tremor. - Sexual dysfunction (delayed ejaculation, decreased libido, anorgasmia). - Serotonin syndrome (rare; with other serotonergic drugs). - SIADH/hyponatremia (elderly, volume-depleted). - QT prolongation (at high doses or with other QT-prolonging drugs). - Suicidality (children, adolescents, young adults) — monitor closely. ## Key Drug Interactions - **MAOIs, linezolid, methylene blue:** Serotonin syndrome. - **Other serotonergics (SSRIs, SNRIs, triptans, St. John’s wort, tramadol):** Increased serotonin risk. - **CYP2D6 substrates (e.g., atomoxetine, metoprolol, risperidone, tamoxifen):** Increased levels of these drugs. - **Warfarin, NSAIDs, antiplatelets:** Increased bleeding risk. - **CYP2C9 substrates (e.g., phenytoin, warfarin):** Inhibited metabolism. - **Benzodiazepines (e.g., alprazolam, diazepam):** Increased sedation. ## Monitoring - Baseline: Psychiatric history, suicidality, weight, liver/renal function. - During therapy: Suicidality (especially first 1–2 months, children/young adults), weight changes, serotonin syndrome symptoms (agitation, hyperthermia, clonus, hyperreflexia), sodium levels (elderly). - Drug levels: Not routinely monitored; may be helpful to rule out toxicity or nonadherence. ## Clinical Pearls - Slow onset: Therapeutic effects in 2–4 weeks; full response may take 8–12 weeks. - Long half-life allows for once-daily dosing; missed doses are less critical, but abrupt discontinuation can still cause withdrawal (dizziness, dysphoria, headache). - Less sedating than other SSRIs; often preferred for patients with fatigue or hypersomnia. - Higher discontinuation rates due to activation and insomnia (take in the morning). - Pregnancy: Fluoxetine is one of the more studied SSRIs in pregnancy; still weigh risks vs. benefits. - Bulimia nervosa: 60 mg fixed dose, no titration required. --- **Disclaimer:** This information is for educational purposes only. Dosing may vary by local protocol, patient-specific factors, and drug availability. Always verify current prescribing information from a reliable drug reference or official manufacturer labeling before making clinical decisions.