Atomoxetine Dosing and Titration for a 16-Year-Old (32 kg) with ASD/ADHD/Anxiety/Insomnia/Tics
Start atomoxetine at 16 mg daily (0.5 mg/kg/day) for 3 days, then increase to 38 mg daily (1.2 mg/kg/day) as the target dose, administered as a single morning dose or split between morning and late afternoon/early evening. 1
Initial Dosing Strategy
Begin with 16 mg daily (0.5 mg/kg/day based on 32 kg body weight) for a minimum of 3 days to assess initial tolerability, particularly given this patient's complex comorbidity profile including anxiety, tics, and autism spectrum disorder. 1
After the initial 3-day period, increase to the target dose of 38 mg daily (1.2 mg/kg/day), which represents the evidence-based target for children and adolescents under 70 kg. 1
The maximum daily dose should not exceed 45 mg (1.4 mg/kg) or 100 mg, whichever is less, though doses above 1.2 mg/kg/day have not demonstrated additional benefit. 1
Timing and Administration
Administer atomoxetine either as a single morning dose or split into two evenly divided doses (morning and late afternoon/early evening) to provide coverage throughout the day and into evening hours. 1
Atomoxetine can be taken with or without food and should be swallowed whole, not opened. 1
A single morning dose has been shown effective into the evening, which may be preferable for this patient to avoid potential interference with the trazodone sleep regimen. 2
Critical Drug Interaction Consideration
This patient is taking citalopram 30 mg, which is a weak-to-moderate CYP2D6 inhibitor. While not as potent as fluoxetine or paroxetine, citalopram may still increase atomoxetine exposure. However, the FDA label specifically addresses "strong" CYP2D6 inhibitors (paroxetine, fluoxetine, quinidine) and does not mandate dose adjustment for weaker inhibitors like citalopram. 1
Monitor closely for increased atomoxetine-related adverse effects (nausea, vomiting, decreased appetite, somnolence) during the first 4 weeks, as citalopram may modestly elevate atomoxetine levels. 1, 2
If symptoms fail to improve after 4 weeks at 38 mg daily and the dose is well tolerated, consider increasing to 45 mg daily (1.4 mg/kg), but only if there are no concerning adverse effects. 1
Expected Timeline and Monitoring
Atomoxetine requires 2-4 weeks before clinical benefits become apparent, unlike stimulants which work immediately—counsel the family accordingly to prevent premature discontinuation. 3
Monitor systematically using standardized ADHD rating scales at baseline, week 4, and week 8 to objectively assess response. 4
Assess cardiovascular parameters (blood pressure and heart rate) at baseline and periodically during treatment, as atomoxetine causes statistically significant but generally not clinically significant increases in both. 2
Efficacy in This Population
Atomoxetine has demonstrated efficacy specifically in children with autism spectrum disorder and comorbid ADHD, with improvements in both hyperactivity (effect size -0.73) and inattention (effect size -0.53). 5
In younger children (ages 3-6) with ASD and ADHD, atomoxetine at 1.2-1.8 mg/kg/day was well tolerated and effective, with 62.4% achieving "very much improved" status and 20.3% "much improved" after 6 months. 6
Advantages for This Specific Patient
Atomoxetine is particularly appropriate for patients with comorbid anxiety and tics, as it does not exacerbate these conditions unlike stimulants which may worsen both. 2, 5
Atomoxetine is less likely than stimulants to worsen insomnia, making it compatible with this patient's existing trazodone regimen for sleep. 2
Atomoxetine has negligible abuse potential and is not a controlled substance, which is relevant for adolescent patients. 2
Common Adverse Effects to Monitor
The most common adverse effects are gastrointestinal (nausea, vomiting, abdominal pain, decreased appetite), headache, and somnolence. 2, 6, 5
In children with ASD specifically, the most frequent adverse events were gastrointestinal (24.1%), aggression or hostility (12.8%), and increased hyperactivity (9.0%). 6
Approximately 17-18% of patients discontinue atomoxetine due to adverse effects, but these typically resolve completely after cessation. 2, 6
Monitor for decreased appetite and weight loss, particularly during the first few months, though this typically stabilizes with continued treatment. 2
Discontinuation
- Atomoxetine can be discontinued abruptly without tapering, as discontinuation is well tolerated with low incidence of withdrawal symptoms or symptom rebound. 1, 2
Addressing the Citalopram Dose
Before optimizing atomoxetine dosing, increase citalopram from 30 mg to 40 mg daily (the FDA-approved maximum for adolescents), as 30 mg represents a suboptimal dose for managing anxiety in this age group. 3 This should be done using 5-10 mg increments at 3-4 week intervals to minimize activation and increased anxiety that can occur with SSRI dose escalation. 4
Trazodone Continuation
Continue trazodone 50 mg at bedtime unchanged, as this dose is well-established for sleep disorders and will not be affected by atomoxetine initiation or discontinuation. 7, 8 Trazodone at 50-100 mg as a single bedtime dose effectively improves sleep without tolerance or REM rebound. 7, 8
Black Box Warning
Be aware that atomoxetine carries a black box warning for suicidal ideation, with meta-analyses showing significantly higher incidence compared to placebo, though the absolute risk remains low. 2 Monitor closely for emergence of suicidal thoughts, particularly during the first few weeks of treatment and after dose increases.