Switching from Adderall 40mg IR to Vyvanse
When converting a patient from Adderall 40mg IR to Vyvanse, start with Vyvanse 50mg once daily in the morning, then titrate by 10mg weekly increments as needed up to a maximum of 70mg daily based on symptom control and tolerability. 1, 2
Conversion Rationale
A conversion factor of approximately 2.5:1 (Vyvanse:Adderall) should be applied, resulting in an initial Vyvanse dose of 50mg for a patient taking 40mg total daily dose of Adderall 1
The FDA-approved starting dose for Vyvanse is typically 30mg once daily, but this represents a de novo initiation rather than a conversion from an established amphetamine dose 2
Since your patient is already on 40mg Adderall IR (which is at the upper end of the therapeutic range for amphetamines), starting at 50mg Vyvanse is appropriate to maintain therapeutic effect 1, 3
Practical Switching Algorithm
Discontinue Adderall 40mg IR abruptly without tapering - no washout period is required when switching between stimulant medications 4
Initiate Vyvanse 50mg once daily in the morning on the day after the last Adderall dose 1, 2
Expect immediate therapeutic effects within hours of the first Vyvanse dose, as both are amphetamine-based stimulants 4
Titrate in 10mg or 20mg increments at weekly intervals if symptom control is inadequate, up to the maximum dose of 70mg daily 2
Key Pharmacokinetic Differences
Lisdexamfetamine (Vyvanse) is a prodrug that must be hydrolyzed to active d-amphetamine after absorption, resulting in a 0.6-hour longer lag time and peak levels occurring 1.1 hours later compared to immediate-release amphetamine 5
Despite the delayed onset, total drug exposure (AUC) and peak concentrations are equivalent between equimolar doses of lisdexamfetamine and d-amphetamine 5
The once-daily dosing of Vyvanse provides full-day coverage up through 6 PM, eliminating the need for multiple daily doses required with Adderall IR 6
Critical Monitoring Parameters
Administer Vyvanse in the morning with or without food; avoid afternoon doses due to potential for insomnia 2
Monitor blood pressure and pulse at baseline and during titration, as cardiovascular effects are similar between amphetamine formulations 5
Assess for common adverse effects including decreased appetite, insomnia, upper abdominal pain, headache, irritability, and weight loss 2, 6
Evaluate symptom control weekly during titration using standardized ADHD rating scales to guide dose adjustments 7, 6
Important Clinical Caveats
The maximum recommended dose of Vyvanse is 70mg daily, which should not be exceeded 2
In patients with severe renal impairment (GFR 15-30 mL/min/1.73 m²), the maximum Vyvanse dose should not exceed 50mg daily 2
Agents that alter urinary pH can impact amphetamine blood levels - acidifying agents decrease levels while alkalinizing agents increase levels, requiring dose adjustments 2
Do not divide a single Vyvanse capsule - the minimum dose is one full capsule per day 2
If the patient cannot swallow capsules, Vyvanse can be opened and mixed with yogurt, water, or orange juice and consumed immediately 2