What is a good starting dose of guanfacine (Extended Release) for a 13-year-old female patient weighing 92 kg with Attention Deficit Hyperactivity Disorder (ADHD) and possible mood or anxiety disorder, currently on methylphenidate, aripiprazole, and sertraline?

Starting Dose of Guanfacine ER for a 92 kg Patient

Start with guanfacine extended-release 1 mg once daily, taken in the evening, regardless of the patient's weight of 92 kg. 1, 2

Rationale for Fixed Starting Dose

• All patients begin at 1 mg daily, which is the FDA-approved and guideline-recommended starting dose for guanfacine ER in ADHD treatment, independent of body weight 1, 2
• The weight-based dosing of 0.1 mg/kg applies to the target maintenance dose range (0.05-0.12 mg/kg/day), not the starting dose 1
• For this 92 kg patient, the weight-based calculation would suggest starting at 9.2 mg, which would be dangerous and far exceeds safety parameters 1

Titration Strategy After Initial Dose

• Increase by 1 mg per week based on response and tolerability, with systematic monitoring of ADHD symptoms using parent and teacher rating scales 1
• The target dose range is 1-7 mg/day (maximum approved dose is 6-7 mg/day depending on jurisdiction) 1
• For this patient weighing 92 kg, the optimal maintenance dose would likely fall in the 4-7 mg range (0.05-0.12 mg/kg/day = 4.6-11 mg, but capped at maximum approved dose) 1, 3
• Higher weight-adjusted doses (>0.08 mg/kg but ≤0.12 mg/kg) may provide additional clinical benefits if tolerated, which for this patient translates to approximately 7-11 mg, though doses above 7 mg exceed current FDA approval 3

Critical Timing Consideration

• Evening administration is strongly preferred to minimize daytime somnolence and fatigue, which are the most common adverse effects (occurring in 38.6% and 15.2% of patients, respectively) 1, 4
• This timing is particularly important for a 13-year-old student to avoid interference with school performance 1

Expected Timeline for Response

• Expect 2-4 weeks before observing clinical benefits, unlike stimulants which work immediately 1
• This delayed onset is a critical counseling point for the patient and family to prevent premature discontinuation 1

Safety Monitoring Requirements

• Obtain baseline blood pressure and heart rate before starting guanfacine 1
• Monitor cardiovascular parameters at each dose adjustment, as guanfacine causes modest decreases in blood pressure (1-4 mmHg) and heart rate (1-2 bpm) 1
• This is particularly important since the patient is already on aripiprazole, which can also affect cardiovascular parameters 1
• Screen for personal and family cardiac history including sudden death, Wolff-Parkinson-White syndrome, hypertrophic cardiomyopathy, and long QT syndrome 1

Drug Interaction Considerations

• The combination with sertraline is generally safe, though both medications can cause somnolence, requiring monitoring for excessive sedation 1, 5
• The combination of guanfacine with methylphenidate is FDA-approved as adjunctive therapy, with evidence demonstrating safety and efficacy 1
• Monitor for opposing cardiovascular effects: methylphenidate increases blood pressure and heart rate while guanfacine decreases both parameters 1

Critical Safety Warning

• Never abruptly discontinue guanfacine—it must be tapered by 1 mg every 3-7 days to avoid rebound hypertension 1, 2
• This is especially important given the patient's higher anticipated maintenance dose 1

Common Pitfalls to Avoid

• Do not use weight-based dosing for the starting dose—this is a common error that could lead to dangerous initial doses in heavier patients 1
• Do not expect immediate effects—families must understand the 2-4 week delay to prevent premature discontinuation 1
• Do not split or crush extended-release tablets—they should be swallowed whole 1
• Do not assume the patient needs a higher starting dose simply because of higher body weight; the 1 mg starting dose applies universally for safety reasons 1, 2