Is switching a 9-year-old boy from guanfacine (Guanfacine) 1mg Extended Release (ER) to Strattera (Atomoxetine) a good plan to manage Attention Deficit Hyperactivity Disorder (ADHD) symptoms, excessive daytime sleepiness, and moodiness, considering his history of excessive weight loss on lisdexamphetamine (Lisdexamfetamine)?

Switching from Guanfacine to Atomoxetine for ADHD with Excessive Daytime Sleepiness

Yes, switching to atomoxetine (Strattera) is an appropriate and evidence-based plan for this child, given that guanfacine is causing excessive daytime sleepiness and moodiness despite good ADHD control, and stimulants caused problematic weight loss. 1

Why Atomoxetine is the Right Choice

Atomoxetine directly addresses the current clinical problem:

• Somnolence is a well-documented adverse effect of alpha-2 agonists like guanfacine, occurring commonly enough to warrant evening dosing recommendations 1
• While atomoxetine can cause initial somnolence if titrated too rapidly, this is transient and far less problematic than the persistent sedation seen with guanfacine 1
• Atomoxetine provides 24-hour symptom coverage without the sedating effects that are limiting this child's quality of life 1, 2
• Given the history of excessive weight loss on lisdexamfetamine, atomoxetine is particularly appropriate as it has fewer appetite and growth effects compared to stimulants 1

Specific Transition Plan

Direct switch without cross-titration:

• Stop guanfacine 1mg ER immediately - there is no evidence requiring a taper for guanfacine at this low dose, and continuing it will perpetuate the sedation problem 1
• Start atomoxetine the same day to maintain ADHD symptom control 3, 2

Starting dose calculation for this 33 kg child:

• Begin with atomoxetine 18mg once daily in the morning (approximately 0.5 mg/kg/day as initial dose) 3, 2
• This conservative starting dose minimizes the risk of initial gastrointestinal side effects and transient somnolence 1, 3
• After minimum 3 days, increase to target dose of 40mg once daily (1.2 mg/kg/day, the recommended target dose) 3, 4, 2
• Can be given as single morning dose or split into morning and late afternoon/early evening doses if needed 1, 3

Critical Monitoring Requirements

Week 1-4 monitoring (most critical period):

• Assess for suicidal ideation weekly - atomoxetine carries an FDA black box warning showing 4 per 1,000 patients develop suicidal thoughts 3
• Watch specifically for: anxiety, agitation, panic attacks, irritability, hostility, impulsivity, or new depression 3
• Monitor for gastrointestinal symptoms (nausea, abdominal pain, vomiting) which are typically transient but more common if dose escalated too rapidly 1, 3

Ongoing monitoring:

• Check blood pressure and heart rate at each visit - atomoxetine causes statistically significant (though usually not clinically significant) increases in both 3, 2
• Monitor for liver injury signs: right upper quadrant pain, dark urine, jaundice, unexplained flu-like symptoms 3
• Assess ADHD symptom response at 4-6 weeks - atomoxetine requires 2-8 weeks for full therapeutic effect, unlike the immediate effect seen with stimulants 4, 2, 5

Expected Timeline and Outcomes

Realistic expectations to discuss with family:

• Sedation should improve within 1-3 days of stopping guanfacine, as the alpha-2 agonist effect wears off 1
• ADHD symptom control may temporarily worsen during the first 2-4 weeks before atomoxetine reaches full efficacy 4, 2, 5
• Full therapeutic benefit expected by 6-8 weeks at target dose 4, 2
• Moodiness should improve as it is likely secondary to the chronic sedation and sleep disruption from guanfacine 1

Important Caveats

Atomoxetine has lower efficacy than stimulants:

• Effect size of approximately 0.7 compared to 1.0 for stimulants 1
• One head-to-head study showed atomoxetine significantly less effective than OROS methylphenidate, though interestingly, treatment-naive children responded similarly to both 2, 5
• However, given this child's excellent prior ADHD control on guanfacine (which also has effect size ~0.7), atomoxetine should provide comparable symptom management 1

If atomoxetine fails after adequate trial (8-12 weeks at target dose):

• Consider extended-release guanfacine dosed in evening only to minimize daytime sedation 1
• Re-evaluate stimulant options with closer weight monitoring and nutritional support 1
• Combination therapy (atomoxetine + low-dose stimulant) could address both weight concerns and efficacy, though this is off-label 1

Absolute contraindications to verify before prescribing:

• Not currently taking or taken within 14 days any MAOI antidepressant 3
• No history of narrow-angle glaucoma 3
• No known pheochromocytoma 3
• No known atomoxetine allergy 3