What is the recommended dosing when switching from Mydayis (amphetamine) 50mg to Vyvanse (lisdexamfetamine)?

Switching from Mydayis 50mg to Vyvanse: Dosing Recommendations

When switching from Mydayis (mixed amphetamine salts) 50mg to Vyvanse (lisdexamfetamine), start with Vyvanse 50-60mg once daily in the morning, as both medications deliver similar amphetamine exposure and Vyvanse is dosed up to 70mg daily for ADHD. 1

Rationale for Dose Conversion

Mydayis 50mg and Vyvanse 50-60mg provide comparable amphetamine delivery:

• Lisdexamfetamine is a prodrug that converts to dextroamphetamine after oral ingestion through enzymatic hydrolysis, with the conversion being rate-limited and gradual 2, 3
• Vyvanse 100mg delivers equimolar amphetamine exposure to 40mg of immediate-release dextroamphetamine, meaning approximately 2.5:1 ratio of lisdexamfetamine to active amphetamine 3
• The FDA-approved dosing range for Vyvanse in ADHD is 30-70mg daily, with dose adjustments in 10-20mg increments at weekly intervals 1

Recommended Switching Strategy

Direct switch approach (preferred for stable patients):

• Discontinue Mydayis 50mg and initiate Vyvanse 50mg the following morning 1
• Alternatively, start at Vyvanse 60mg if the patient requires robust symptom control throughout the day 1
• Take Vyvanse in the morning with or without food; avoid afternoon dosing due to insomnia risk 1

Titration approach (if uncertain about equivalency):

• Start Vyvanse at 40mg and increase by 10mg weekly based on response, up to maximum 70mg daily 1
• This conservative approach minimizes risk of under- or over-dosing during transition 4

Pharmacokinetic Considerations

Vyvanse has a delayed onset compared to immediate-release amphetamines:

• Peak amphetamine concentrations occur approximately 1 hour later with lisdexamfetamine versus immediate-release dextroamphetamine 3
• The lag time for plasma concentration increase is 0.6 hours longer with lisdexamfetamine 3
• Duration of effect extends to 14 hours post-dose in adults, providing all-day coverage 5

Monitoring During Transition

Assess the following parameters weekly during the first month:

• ADHD symptom control throughout the day, particularly late afternoon/evening coverage 5
• Blood pressure and heart rate at each visit (quarterly thereafter once stable) 6
• Appetite and weight at each visit, as appetite suppression is dose-dependent 1
• Sleep quality and insomnia symptoms, given morning-only dosing requirement 1
• Emergence of irritability, anxiety, or mood changes 1

Common Pitfalls to Avoid

Do not start at 30mg Vyvanse when switching from Mydayis 50mg:

• This represents significant under-dosing and will likely result in inadequate symptom control 1
• The FDA recommends 30mg as a starting dose for stimulant-naive patients, not for those already on therapeutic amphetamine doses 1

Do not divide or split Vyvanse capsules for "in-between" doses:

• The FDA explicitly states not to take less than one capsule per day and that a single dose should not be divided 1
• If dose adjustment needed, use the available strengths (10,20,30,40,50,60, 70mg) 1

Do not administer Vyvanse in the afternoon:

• Unlike Mydayis which may have been dosed differently, Vyvanse must be taken in the morning to avoid insomnia 1

Dose Adjustments Based on Response

If inadequate response at Vyvanse 50-60mg:

• Increase to 70mg (maximum FDA-approved dose for ADHD) after at least one week 1
• Allow minimum one week between dose increases to properly evaluate response 6

If excessive side effects occur:

• Reduce dose by 10mg increments 1
• Consider that peak subjective effects and cardiovascular stimulation are similar between equimolar doses of lisdexamfetamine and dextroamphetamine 3