How should I switch a patient from guanfacine immediate‑release (IR) to guanfacine extended‑release (ER)?

Switching from Guanfacine IR to ER

You can directly switch from guanfacine immediate-release to the extended-release formulation at an equivalent total daily dose without cross-tapering or dose adjustment, starting the ER formulation the day after stopping IR. 1

Direct Conversion Protocol

• Calculate the total daily IR dose and initiate ER at that same milligram amount given once daily 1, 2
• Administer ER in the evening to minimize daytime somnolence and fatigue, which are the most common adverse effects 1, 2
• Start ER the morning after the last IR dose if morning administration is preferred, or the evening of the same day the last morning IR dose was given 1

Pharmacokinetic Rationale

The pharmacokinetic profiles support direct conversion because:

• Guanfacine ER provides steady 24-hour coverage with once-daily dosing, eliminating the need for multiple daily IR doses 1, 2
• Plasma levels at 24 hours post-dose are equivalent between 3 mg IR and 4 mg ER formulations, though this represents a slight dose increase rather than exact equivalence 3
• The half-life of guanfacine (approximately 17 hours) is similar across both IR and ER formulations, facilitating straightforward conversion 4

Dosing Considerations

• For patients on IR doses that don't match available ER tablet strengths (1,2,3,4 mg), round to the nearest available ER dose 2, 4
• If the patient was taking divided IR doses totaling more than 4 mg daily, you may need to use the maximum ER dose of 4 mg initially, then titrate upward by 1 mg weekly to a maximum of 6-7 mg/day based on response 1, 2
• The target therapeutic range remains 0.05-0.12 mg/kg/day regardless of formulation 1, 2

Critical Safety Points

• No tapering is required when switching between formulations because both contain the same active drug and the ER formulation does not carry significant rebound hypertension risk upon conversion 5
• However, never abruptly discontinue guanfacine ER itself—if stopping the medication entirely, taper by 1 mg every 3-7 days to avoid rebound hypertension 1, 2
• Monitor blood pressure and heart rate at the first follow-up visit after conversion, as ER formulations cause modest decreases (1-4 mmHg BP, 1-2 bpm HR) 1, 6

Expected Timeline and Monitoring

• Therapeutic effects require 2-4 weeks to emerge fully, so do not expect immediate changes in symptom control during the conversion period 1, 2
• Counsel families that the ER formulation provides around-the-clock coverage, unlike IR which may have gaps between doses 1, 2
• Schedule follow-up within 1-2 weeks to assess tolerability, particularly somnolence, and verify adequate symptom control throughout the day 1

Common Pitfalls to Avoid

• Do not reduce the dose when converting to ER unless the patient experienced dose-limiting side effects on IR; the goal is equivalent daily exposure 3, 4
• Do not split, crush, or chew ER tablets—they must be swallowed whole to maintain extended-release properties 2
• Do not assume immediate symptom improvement—the delayed onset (2-4 weeks) applies even when switching formulations 1, 2