Lisdexamfetamine (Vyvanse) to Adderall Conversion Dosing
When switching from Vyvanse (lisdexamfetamine) to Adderall (mixed amphetamine salts), a 50 mg dose of Vyvanse is approximately equivalent to 20 mg of Adderall.
Pharmacological Basis for Conversion
Lisdexamfetamine is a prodrug that is enzymatically converted to active d-amphetamine after oral administration. This conversion occurs through rate-limited hydrolysis in the body, where l-lysine is cleaved to gradually release the pharmacologically active d-amphetamine component 1.
The conversion between Vyvanse and Adderall requires understanding their pharmacokinetic differences:
- Vyvanse contains lisdexamfetamine which is converted to d-amphetamine
- Adderall contains a mixture of d-amphetamine and l-amphetamine salts (75% dextroamphetamine and 25% levoamphetamine)
- The conversion factor accounts for both the prodrug nature of Vyvanse and the mixed salt composition of Adderall
Dose Equivalence Table
| Vyvanse (lisdexamfetamine) | Adderall (mixed amphetamine salts) |
|---|---|
| 30 mg | 10-12.5 mg |
| 50 mg | 20 mg |
| 70 mg | 25-30 mg |
Clinical Considerations When Switching
Timing Considerations
- Vyvanse has a delayed onset of action compared to immediate-release Adderall
- Research shows that lisdexamfetamine reaches peak plasma levels approximately 1.1 ± 1.5 hours later than immediate d-amphetamine 1
- When switching, consider that Vyvanse's effects may last 10-14 hours while Adderall IR lasts 4-6 hours and Adderall XR lasts 8-12 hours
Dosing Strategy
- Initial conversion: Use the equivalence table above as a starting point
- Titration: Adjust dose based on clinical response and side effects
- Formulation selection: Consider whether Adderall IR or XR is more appropriate based on the patient's needs
Monitoring Parameters
- Blood pressure and heart rate (stimulants typically increase heart rate by 1-2 beats per minute and blood pressure by 1-4 mmHg) 2
- Appetite and weight
- Sleep quality
- Emergence of side effects
Important Clinical Caveats
- Bioavailability differences: While the total exposure (AUC) of active amphetamine is similar between equivalent doses of Vyvanse and d-amphetamine, the pharmacokinetic profile differs 1
- Abuse potential considerations: Lisdexamfetamine may have less abuse potential compared to immediate-release dextroamphetamine/amphetamine formulations due to its prodrug nature 3
- Individual variability: Some patients may require dose adjustments due to individual metabolism differences
- Contraindications: Both medications are contraindicated in patients with advanced cardiovascular disease, high blood pressure, hyperthyroidism, glaucoma, agitation, history of substance abuse, or history of psychosis or mania 2
Special Populations
- Children and adolescents: Follow the same conversion principles but start at the lower end of the dosing range
- Elderly patients: Use lower starting doses and titrate more gradually due to increased sensitivity to cardiovascular effects 2
- Patients with cardiac conditions: Consider non-stimulant alternatives such as atomoxetine, guanfacine, or clonidine if cardiovascular risk is significant 2
Remember that the conversion is approximate, and clinical response should guide final dosing decisions.