What is the appropriate dosing of atomoxetine (Strattera) for a 16‑year‑old female weighing 105 lb (≈48 kg)?

Atomoxetine Dosing for a 16-Year-Old Female, 105 lbs (48 kg)

Start atomoxetine at approximately 0.5 mg/kg/day (25 mg daily) for the first 3 days, then increase to a target dose of 1.2 mg/kg/day (approximately 60 mg daily), administered either as a single morning dose or divided into two doses (morning and late afternoon/early evening). 1

Initial Dosing Strategy

For children and adolescents weighing ≤70 kg (which includes this patient at 48 kg):

• Starting dose: Begin at approximately 0.5 mg/kg/day (~25 mg daily) for a minimum of 3 days
• Target dose: Increase to 1.2 mg/kg/day (~60 mg daily)
• Maximum dose: Can titrate up to 1.4 mg/kg/day or 100 mg daily (whichever is less) if needed after 2-4 weeks at target dose 1

For this 48 kg patient, the specific dosing would be:

• Start: 25 mg daily
• Target: 60 mg daily (1.2 mg/kg × 48 kg = 57.6 mg, round to 60 mg)
• Maximum if needed: 67 mg daily (1.4 mg/kg × 48 kg)

Dosing Schedule Options

You can administer atomoxetine in two ways with equivalent efficacy 1:

1. Once-daily morning dosing: The entire daily dose given in the early morning (preferred for simplicity and adherence)
2. Divided dosing: Split the total daily dose into two administrations—early morning and late afternoon/early evening

Clinical trials demonstrated that once-daily morning administration is effective and may improve adherence 1. The divided dosing approach was used in studies showing efficacy at 1.2-1.8 mg/kg/day 1, 2.

Evidence Supporting 1.2 mg/kg/day as Target

The FDA label and pivotal trials clearly establish that 1.2 mg/kg/day is the optimal initial target dose 1, 2:

• In dose-response studies, 1.2 mg/kg/day and 1.8 mg/kg/day showed statistically superior efficacy compared to placebo
• Critically, 1.8 mg/kg/day provided no additional benefit over 1.2 mg/kg/day 1, 2
• The 0.5 mg/kg/day dose was not superior to placebo 1, 2
• Mean effective doses in clinical trials ranged from 1.3-1.6 mg/kg/day 1

Titration Timeline

• Wait at least 3 days at starting dose before increasing
• After reaching target dose (1.2 mg/kg/day), assess response for 2-4 weeks
• If inadequate response after 2-4 weeks at target, may increase to maximum dose (1.4 mg/kg/day or 100 mg daily, whichever is less)
• Avoid rapid dose escalation to minimize gastrointestinal side effects and somnolence 3

Critical Safety Monitoring

Before initiating atomoxetine 3:

• Obtain personal and family cardiac history (sudden death, cardiovascular symptoms, Wolff-Parkinson-White syndrome, hypertrophic cardiomyopathy, long QT syndrome)
• If cardiac risk factors present, obtain ECG and consider cardiology referral
• Monitor heart rate and blood pressure at baseline and during treatment (atomoxetine increases HR and BP in 5-15% of patients)

Black box warning: Monitor for emergence of suicidal ideation, particularly in the first few months of treatment 3.

Common adverse effects include initial somnolence, gastrointestinal symptoms (especially with rapid titration), and decreased appetite 3. Extremely rarely, hepatitis has been reported 3.

Duration of Action

Atomoxetine provides 24-hour symptom coverage with once-daily dosing in children and adolescents, with effects extending throughout waking hours and into the next morning 4, 5.