What is the appropriate atomoxetine dose for a 25-year-old male weighing 136.6 lb (approximately 62 kg)?

Atomoxetine Dosing for a 25-Year-Old Female Weighing 136.6 lbs (62 kg)

Start atomoxetine at 40 mg once daily in the morning, then increase after a minimum of 3 days to a target dose of 80 mg daily (either as a single morning dose or split into morning and late afternoon/evening doses), with a potential increase to 100 mg daily after 2-4 additional weeks if response is inadequate. 1

Initial Dosing Strategy

• For adults and adolescents over 70 kg body weight (this patient is 62 kg, but adult dosing applies at age 25), atomoxetine should be initiated at 40 mg total daily dose 1
• After a minimum of 3 days, increase to the target dose of 80 mg daily 1
• The 80 mg dose can be administered either as a single morning dose or divided into morning and late afternoon/evening doses 1

Dose Escalation Timeline

• If optimal response is not achieved after 2-4 additional weeks at 80 mg, the dose may be increased to a maximum of 100 mg daily 1
• The maximum recommended total daily dose in adults is 100 mg 1
• There are no data supporting increased effectiveness at doses higher than 100 mg 1

Administration Considerations

• Atomoxetine may be taken with or without food 1
• Capsules should be swallowed whole and not opened 1
• Once-daily dosing is generally preferred for convenience and adherence 2, 3
• The drug has a 24-hour duration of effect, making single daily dosing feasible 2

Monitoring Requirements

• Assess ADHD symptom improvement after 3-4 weeks at target dose 2
• Monitor for cardiovascular effects: atomoxetine causes modest increases in heart rate (mean 5-10 bpm) and blood pressure (mean 2-4 mmHg systolic/diastolic) 2, 3
• Screen for suicidal ideation, particularly in the first few months of treatment, as atomoxetine carries a black-box warning for increased suicidal thoughts (incidence approximately 0.4% vs 0% with placebo) 2
• Check for hepatotoxicity if symptoms of liver injury develop (jaundice, dark urine, right upper quadrant tenderness), though this is rare 2

Common Adverse Effects to Counsel About

• Most frequent side effects in adults: dry mouth (21%), insomnia (15%), nausea (12%), decreased appetite (11%), constipation (8%), dizziness (6%), sweating (5%), dysuria (6%), sexual dysfunction (2%), and palpitations 4, 5
• Most adverse events are mild to moderate and often diminish with continued treatment 2, 3
• Discontinuation rates due to adverse events are approximately 7-9% in adults 4, 5

Expected Efficacy Timeline

• Statistically significant improvement may occur within 2 weeks, but clinically meaningful improvement typically requires 4-6 weeks at therapeutic doses 2
• Maximal benefit is usually achieved by 8-12 weeks 2
• In adult trials, atomoxetine reduced total ADHD symptom scores by 28-30% compared to 18-20% with placebo 4, 5

Special Considerations for This Patient

• At 62 kg body weight, this patient falls below the 70 kg threshold, but adult dosing (40 mg starting dose) is still appropriate given her age of 25 years 1
• If she were to be dosed by weight (pediatric approach), the calculation would be 0.5 mg/kg initially (31 mg) titrated to 1.2 mg/kg (74 mg), but the adult fixed-dose regimen is simpler and FDA-approved for this age 1
• No dose adjustment is needed for normal renal or hepatic function 1

Contraindications and Drug Interactions to Screen For

• Absolute contraindication: concurrent use or use within 14 days of MAOIs due to risk of hypertensive crisis 1
• Use with caution in patients with hypertension, tachycardia, cardiovascular disease, or cerebrovascular disease 3
• CYP2D6 inhibitors (paroxetine, fluoxetine, quinidine) significantly increase atomoxetine exposure; if the patient is taking these or is a known CYP2D6 poor metabolizer, start at 40 mg and increase to 80 mg only after 4 weeks if symptoms fail to improve and the initial dose is well tolerated 1

Discontinuation

• Atomoxetine can be discontinued without tapering, as it is not associated with significant withdrawal symptoms or rebound 1, 2
• Discontinuation-emergent adverse events are rare 2

Common Pitfalls to Avoid

• Do not increase the dose too rapidly: wait at least 3 days before the first increase and 2-4 weeks before considering the maximum dose 1
• Do not exceed 100 mg daily in adults, as higher doses do not improve efficacy and increase adverse effects 1
• Do not use atomoxetine as monotherapy if the patient has untreated bipolar disorder, as it may precipitate mania; screen for personal or family history of bipolar disorder before initiating 1
• Do not assume immediate efficacy: counsel the patient that full therapeutic benefit requires 4-8 weeks at target dose 2