What is the recommended dose of fluoxetine (selective serotonin reuptake inhibitor) for a teenager?

Fluoxetine Dosing for Teenagers

For teenagers with major depressive disorder, start fluoxetine at 10 mg daily for one week, then increase to the target dose of 20 mg daily, with a maximum dose of 60 mg/day if needed after several weeks of insufficient response. 1, 2

Initial Dosing Strategy

• Begin with 10 mg daily as a "test dose" to monitor for initial adverse effects such as anxiety or agitation, which are common early side effects of SSRIs 1
• After one week at 10 mg/day, increase to the therapeutic target of 20 mg daily 2
• In lower weight children, the starting and target dose may remain at 10 mg/day due to higher plasma levels 2

Dose Titration and Optimization

• Wait 3-4 weeks between dose adjustments due to fluoxetine's exceptionally long half-life (1-3 days for parent compound, 7-15 days for active metabolite) 1, 3
• If insufficient clinical improvement occurs after several weeks at 20 mg/day, consider increasing the dose 2
• The dose range is 20-60 mg/day for adolescents, with a maximum of 80 mg/day (though higher doses increase adverse effects) 2, 4
• The full therapeutic effect may be delayed until 4-5 weeks of treatment or longer 2

Critical Safety Monitoring

• Monitor intensively for suicidal ideation and behavior, especially during the first months of treatment and within 24-48 hours after any dosage changes 1
• All SSRIs carry a black box warning for suicidal thinking and behavior through age 24 years 1
• Watch for behavioral activation, anxiety, agitation, or switch to mania, particularly early in treatment 5
• Ensure parental oversight of medication administration in adolescents 6

Common Adverse Effects

• Most frequent side effects at 20 mg/day include nausea, nervousness, insomnia, and headache 3, 7
• Fluoxetine is activating; side effects may not manifest for several weeks due to the long half-life 5
• Higher doses (above 20 mg/day) are associated with increased adverse events and higher dropout rates 4, 7

Important Drug Interactions and Precautions

• Exercise extreme caution with other serotonergic drugs due to serotonin syndrome risk 5
• Fluoxetine inhibits CYP2D6 and other cytochrome P450 enzymes, potentially causing drug interactions 5, 4
• Use with caution in patients with congenital long QT syndrome or family history of sudden cardiac death 5
• Wait at least 14 days after stopping an MAOI before starting fluoxetine, and at least 5 weeks after stopping fluoxetine before starting an MAOI 2

Duration of Treatment

• Continue treatment for 4-12 months after first episode of major depressive disorder 5
• Maintenance therapy may extend beyond initial acute treatment to prevent relapse 2

Discontinuation

• Taper slowly when discontinuing, though fluoxetine's long half-life makes withdrawal syndrome less likely than with shorter-acting SSRIs 5
• The extended half-life essentially precludes a significant withdrawal phenomenon 4