What is the comparable dose of Vyvanse (lisdexamfetamine) to Adderall XR (amphetamine and dextroamphetamine) 15 mg in an adult patient with Attention Deficit Hyperactivity Disorder (ADHD)?

Dose Conversion: Adderall XR to Vyvanse

The comparable dose of Vyvanse to Adderall XR 15 mg is 30 mg, based on the approximate 2:1 conversion ratio between lisdexamfetamine and amphetamine salts.

Conversion Rationale

The conversion from Adderall XR to Vyvanse (lisdexamfetamine) follows a well-established pharmacokinetic principle: lisdexamfetamine is a prodrug that must be metabolized to d-amphetamine to become therapeutically active 1. This metabolic conversion results in approximately half the amount of active d-amphetamine compared to the parent compound by weight.

Standard Conversion Formula

• Use a 2:1 ratio when converting from Adderall XR to Vyvanse - multiply the Adderall XR dose by 2 to determine the equivalent Vyvanse dose 1
• For Adderall XR 15 mg, the equivalent Vyvanse dose is 30 mg once daily in the morning 2, 1
• This conversion accounts for the fact that lisdexamfetamine must be enzymatically cleaved to release d-amphetamine, resulting in lower bioavailability of active drug per milligram 1

Pharmacokinetic Differences to Consider

While the 2:1 conversion provides a starting point, important pharmacokinetic differences exist between these formulations:

• Vyvanse has a longer duration of action compared to Adderall XR, with efficacy demonstrated up to 12-13 hours post-dose, whereas Adderall XR typically provides 8-12 hours of coverage 1
• Peak plasma concentrations occur later with Vyvanse (approximately 3.5 hours after oral administration) compared to Adderall XR (approximately 3 hours for the immediate-release component) 3, 1
• The prodrug mechanism of lisdexamfetamine results in a smoother pharmacokinetic profile with less pronounced peaks and troughs 1

Titration After Conversion

After switching to Vyvanse 30 mg, monitor response and adjust as needed:

• Allow at least one week at the initial converted dose before making adjustments to properly evaluate therapeutic response 4, 5
• If symptom control is inadequate, increase in 10 mg increments weekly up to a maximum of 70 mg daily 1
• The therapeutic dose range for adults typically falls between 30-70 mg daily 1

Critical Monitoring Parameters

When making this conversion, systematically assess:

• ADHD symptom control using standardized rating scales (ADHD-RS or CAARS) at baseline and after one week 6, 7
• Cardiovascular parameters including blood pressure and pulse at each visit 4, 6
• Common adverse effects including decreased appetite, insomnia, headache, and irritability - these are typical of amphetamine products but may differ in intensity or timing with the prodrug formulation 1
• Duration of symptom coverage throughout the day, as Vyvanse may provide longer afternoon/evening coverage than the previous Adderall XR regimen 1

Common Pitfalls to Avoid

• Do not use a 1:1 conversion ratio - this will result in underdosing and inadequate symptom control 1
• Avoid afternoon or evening dosing - administer Vyvanse upon awakening to minimize sleep disturbances, as the extended duration of action increases insomnia risk with late dosing 2, 1
• Do not split or divide the capsule dose - Vyvanse capsules should be taken whole or the entire contents sprinkled on applesauce and consumed immediately 2
• Do not assume immediate equivalence - individual response varies, and some patients may require dose adjustment above or below the calculated conversion dose 1

Special Considerations

• Patients with active substance use disorder: Vyvanse has demonstrated lower abuse liability compared to immediate-release amphetamines due to its prodrug mechanism, making it a potentially safer option in this population 4, 8
• Patients requiring extended daily coverage: The longer duration of action with Vyvanse may eliminate the need for afternoon supplementation that some patients require with Adderall XR 1