Can a patient with Attention Deficit Hyperactivity Disorder (ADHD) taking guanfacine (Intuniv is an extended-release formulation of guanfacine) 1mg twice daily (bid) be switched to Intuniv (guanfacine extended-release)?

Switching from Immediate-Release Guanfacine to Intuniv (Guanfacine Extended-Release)

Yes, you can switch your patient from guanfacine 1mg twice daily to Intuniv (guanfacine extended-release), but you cannot simply convert on a mg-for-mg basis—the extended-release formulation has different pharmacokinetics and requires dose adjustment. 1

Critical Pharmacokinetic Difference

Guanfacine extended-release is NOT substitutable on a mg-for-mg basis with immediate-release guanfacine due to different pharmacokinetics. 1 This is the most important consideration when making this switch.

Recommended Conversion Strategy

Starting Dose

• Begin Intuniv at 1mg once daily in the evening (not 2mg total daily dose) 2, 3
• Evening administration is strongly preferred to minimize daytime somnolence and fatigue, which are the most common adverse effects 2
• The patient is currently receiving 2mg total daily of immediate-release, but you should start conservatively with the extended-release formulation 1

Titration Protocol

• Titrate by 1mg weekly increments based on response and tolerability 2
• Target dose range is 0.05-0.12 mg/kg/day or 1-7mg/day maximum 2
• Most patients achieve therapeutic benefit between 1-4mg daily 4, 1

Timeline Expectations

• Counsel the patient that therapeutic effects require 2-4 weeks to emerge, unlike the immediate effects they may have experienced with the immediate-release formulation 4, 2
• This delayed onset is critical for setting appropriate expectations and preventing premature discontinuation 2

Advantages of Switching to Extended-Release

• "Around-the-clock" symptom control with once-daily dosing eliminates the need for twice-daily administration and provides more consistent coverage 4, 2
• Improved medication adherence due to simplified dosing schedule 4
• More stable plasma levels throughout the day, potentially reducing peak-related side effects 1

Essential Monitoring Requirements

Cardiovascular Parameters

• Obtain baseline blood pressure and heart rate before initiating Intuniv 2
• Monitor BP and HR at each dose adjustment 2
• Expect modest decreases: 1-4 mmHg in BP and 1-2 bpm in HR 2
• Screen for personal or family history of cardiac conditions including Wolf-Parkinson-White syndrome, sudden death, hypertrophic cardiomyopathy, and long QT syndrome 2

Symptom Assessment

• Monitor ADHD symptoms systematically at each dose adjustment using parent and teacher reports 2
• Assess for common adverse effects: somnolence (most common), fatigue, headache, dry mouth, dizziness, irritability, and abdominal pain 2, 3

Critical Safety Warning About Discontinuation

Never abruptly stop guanfacine extended-release—it must be tapered by 1mg every 3-7 days to avoid rebound hypertension. 2, 3 This applies even though the immediate-release formulation shows low frequency of rebound hypertension 3. The extended-release formulation requires the same precautions 2.

Common Pitfalls to Avoid

• Do not assume 2mg ER equals 2mg total daily IR—start at 1mg ER and titrate up based on response 1
• Do not expect immediate therapeutic effects—allow 2-4 weeks at optimized dose before assessing efficacy 2
• Do not administer in the morning—evening dosing minimizes daytime sedation that could interfere with daily functioning 2
• Do not crush or split the extended-release tablets—they must be swallowed whole to maintain the extended-release properties 2

Drug Interactions to Consider

• CYP3A4 inhibitors (e.g., erythromycin, fluconazole) require decreasing GXR to 50% of usual target dose 5
• CYP3A4 inducers (e.g., efavirenz) may require titrating up to double the usual target dose over 1-2 weeks 5
• CNS depressants (phenothiazines, barbiturates, benzodiazepines, alcohol) have additive sedative effects 3

When Extended-Release Is Particularly Appropriate

• Comorbid sleep disorders—the sedating properties improve sleep onset when administered at bedtime 4, 2
• Comorbid tic disorders or Tourette's—guanfacine treats both ADHD and tics without worsening tic severity 4, 2
• Substance use disorder risk—guanfacine is uncontrolled, making it preferable in populations at risk for diversion 4, 2
• Disruptive behavior disorders—may be preferred as first-line when ADHD co-occurs with oppositional symptoms 4, 2