What dose of Adderall immediate-release (mixed amphetamine salts) can be given to a patient currently taking Vyvanse (lisdexamfetamine) 40 mg daily?

Amphetamine Dose Conversion: Vyvanse to Adderall IR

A patient on Vyvanse 40 mg can be given approximately 10-15 mg of Adderall IR per dose, with a maximum total daily dose not exceeding 40 mg of amphetamine.

Understanding the Conversion

Vyvanse (lisdexamfetamine) 40 mg is a prodrug that converts to approximately 12 mg of active d-amphetamine after enzymatic hydrolysis 1. However, direct dose conversion is not straightforward because:

• Vyvanse provides extended-release coverage (up to 13 hours) through its prodrug mechanism 2, 3
• Adderall IR requires multiple daily doses (typically 2-3 times daily) due to its 4-6 hour duration 4

Practical Dosing Strategy

Starting Approach

• Begin with 5 mg Adderall IR twice daily (morning and noon) 4
• This conservative start allows assessment of tolerance and response
• The starting dose of 2.5-5 mg per dose is standard for amphetamine formulations 4

Titration Guidelines

• Increase in 2.5-5 mg increments weekly if symptom control is inadequate 4
• Monitor for both efficacy and side effects at each dose adjustment
• Maximum recommended total daily dose is 40 mg for amphetamines per FDA guidelines and expert consensus 4

Typical Maintenance Range

For a patient previously on Vyvanse 40 mg:

• Total daily Adderall IR: 20-30 mg divided into 2-3 doses
• Example regimen: 10 mg morning, 10 mg noon, optional 5-10 mg afternoon
• Some patients may require up to 40 mg total daily dose 4

Critical Monitoring Points

Cardiovascular surveillance is mandatory:

• Check blood pressure and pulse at each titration visit 4
• Adults should have quarterly vital sign monitoring 4

Common side effects to assess:

• Appetite suppression (more pronounced with amphetamines than methylphenidate) 4
• Insomnia (particularly with late-day dosing)
• Weight loss, anxiety, irritability 4

Dose-limiting adverse events requiring dose reduction or discontinuation include:

• Severe anorexia, insomnia >1.5 hours, marked tics, severe headaches, or psychosis 4

Important Caveats

Why Not Simply Convert mg-for-mg?

The patient was receiving Vyvanse 40 mg (equivalent to ~12 mg d-amphetamine), but this does not mean they should receive 12 mg of Adderall IR. The prodrug delivery system of Vyvanse provides smoother, prolonged coverage that cannot be replicated with immediate-release formulations 2, 3.

Individual Variability

Recent meta-analyses demonstrate that flexible-dose titration strategies produce better outcomes than fixed-dose approaches 5. The optimal dose varies significantly between individuals based on:

• Symptom severity and response
• Tolerability of side effects
• Coverage needs throughout the day

Abuse Potential Consideration

Adderall IR has higher abuse potential than Vyvanse due to its immediate-release formulation 1. Monitor for signs of misuse, diversion, or requests for early refills, particularly in adolescents and young adults 6.

Maximum Dose Boundaries

While the PDR lists 40 mg as the maximum daily amphetamine dose, expert consensus acknowledges that some patients may require higher doses (up to 0.9 mg/kg or 65 mg daily in adults) 4. However, such doses require clear documentation that lower doses were inadequate and that higher doses are not causing problematic side effects (weight loss, blood pressure elevation, agitation) 4.

Algorithm for Dose Selection

1. Start conservative: 5 mg Adderall IR twice daily
2. Assess weekly: Use standardized ADHD rating scales
3. Titrate upward: Increase by 2.5-5 mg per dose if inadequate response
4. Monitor tolerability: Check vital signs and side effects at each visit
5. Target range: 20-30 mg total daily (divided doses) for most patients previously on Vyvanse 40 mg
6. Maximum ceiling: 40 mg total daily per standard guidelines; document justification if exceeding