What is the equivalent dose of Vyvanse (lisdexamfetamine) for Adderall (amphetamine/dextroamphetamine) 20mg twice daily (BID)?

Equivalent Dose of Vyvanse for Adderall 20mg BID

The equivalent dose of Vyvanse (lisdexamfetamine) for Adderall (amphetamine/dextroamphetamine) 20mg twice daily (40mg total daily dose) is approximately 50-70mg once daily.

Pharmacological Comparison

Lisdexamfetamine (Vyvanse) is a prodrug that is converted to dextroamphetamine in the bloodstream through enzymatic hydrolysis primarily by red blood cells 1. This conversion process results in several key differences from Adderall:

• Onset and Duration: Vyvanse has a longer lag time (approximately 0.6 hours) and reaches peak levels about 1.1 hours later than immediate-release Adderall 2
• Metabolism: After oral ingestion, lisdexamfetamine is hydrolyzed to l-lysine and active d-amphetamine 3
• Duration of Action: Vyvanse provides approximately 14 hours of coverage in adults 4, compared to 4-6 hours for immediate-release Adderall

Dosage Conversion Rationale

When converting from Adderall to Vyvanse, several factors should be considered:

1. Total Daily Amphetamine Exposure: Adderall 20mg BID provides a total daily dose of 40mg of mixed amphetamine salts

2. Bioavailability Comparison:

   • Vyvanse is completely converted to dextroamphetamine with consistent bioavailability 1
   • The pharmacokinetic studies show that equimolar doses of lisdexamfetamine and d-amphetamine result in similar total exposure (AUC) 2

3. Extended-Release Properties:

   • Vyvanse is designed for once-daily dosing 1
   • Adderall XR 20mg once daily is bioequivalent to Adderall IR 10mg twice daily 5

Recommended Conversion Approach

1. Starting Dose: Begin with Vyvanse 50mg once daily in the morning

   • This aligns with the FDA-approved dosing guidelines for Vyvanse, which recommend starting at 30mg and titrating up to 50-70mg 1
   • The American Academy of Child and Adolescent Psychiatry supports this dosing range 6

2. Titration: If needed, adjust the dose after 1 week based on clinical response

   • Maximum recommended daily dose is 70mg 1
   • Dose adjustments should be made in increments of 10-20mg 1

3. Administration: Take Vyvanse in the morning with or without food 1

   • Avoid afternoon doses to prevent insomnia
   • Can be taken as a whole capsule or mixed with yogurt, water, or orange juice 1

Important Clinical Considerations

• Renal Impairment: For patients with severe renal impairment (GFR 15-30 mL/min/1.73m²), maximum dose should not exceed 50mg daily; for ESRD, maximum is 30mg daily 1

• Monitoring Parameters: Regularly assess:

  • Blood pressure and heart rate
  • Weight and appetite
  • Sleep quality
  • Growth parameters in pediatric patients 6

• Drug Interactions: Agents that alter urinary pH can impact amphetamine levels:

  • Acidifying agents decrease blood levels
  • Alkalinizing agents increase blood levels 1

Potential Advantages of Switching

1. Convenience: Once-daily dosing may improve adherence compared to twice-daily Adderall
2. Extended Coverage: Vyvanse provides up to 14 hours of symptom control 4
3. Smoother Effect: The gradual conversion to active d-amphetamine may provide more consistent effects throughout the day

Remember that individual response to stimulants varies, and close monitoring during the transition period is essential to ensure optimal symptom control and minimize side effects.