Equivalent Vyvanse Dosage for Adderall IR 20mg BID
The equivalent dose of Vyvanse (lisdexamfetamine) for a patient taking Adderall IR (amphetamine salts) 20mg twice daily is 70mg once daily.
Conversion Rationale
When converting between amphetamine formulations, it's important to understand their pharmacokinetic differences:
- Adderall IR 20mg BID provides a total daily dose of 40mg of mixed amphetamine salts
- Vyvanse (lisdexamfetamine) is a prodrug that converts to dextroamphetamine in the bloodstream
- Vyvanse 70mg contains approximately 40.5mg of lisdexamfetamine base 1
- When metabolized, this produces an amount of dextroamphetamine roughly equivalent to 40mg of mixed amphetamine salts (Adderall)
Pharmacokinetic Considerations
Vyvanse has several distinct pharmacokinetic properties compared to Adderall IR:
- Vyvanse has a longer duration of action (approximately 12 hours) versus Adderall IR's 4-6 hours 1
- Vyvanse has a delayed peak effect (Tmax of dextroamphetamine is approximately 3.5-4.5 hours) 1
- Vyvanse provides smoother plasma concentrations without the peaks and troughs associated with twice-daily Adderall IR dosing 2
Dosing Guidelines
The FDA-approved dosing for Vyvanse indicates:
- Starting dose is typically 30mg once daily in the morning 1
- Dosage may be adjusted in increments of 10mg or 20mg at approximately weekly intervals 1
- Maximum recommended dosage is 70mg once daily 1
When transitioning from Adderall IR 20mg BID (40mg total daily dose), the equivalent Vyvanse dose would be 70mg once daily. This provides comparable total amphetamine exposure over 24 hours.
Administration Recommendations
- Take Vyvanse once daily in the morning with or without food 1
- Avoid afternoon doses because of potential insomnia 1
- Vyvanse capsules can be swallowed whole or opened and mixed with yogurt, water, or orange juice 1
Clinical Considerations
- Patients may experience a different onset and duration of effect when switching from Adderall IR to Vyvanse
- The onset of action for Vyvanse is approximately 1.5 hours after administration 3
- The single daily dosing of Vyvanse may improve adherence compared to multiple daily Adderall IR doses 4
- Both medications have similar side effect profiles, including decreased appetite, insomnia, and potential cardiovascular effects 5
Monitoring Recommendations
When switching from Adderall IR to Vyvanse:
- Monitor for changes in symptom control throughout the day
- Assess for side effects including changes in blood pressure, heart rate, sleep quality, and appetite
- Regular monitoring of vital signs, weight, and height (in children) is recommended 5
- Titration may be necessary to find the optimal dose for the individual patient
Common Pitfalls to Avoid
- Assuming immediate equivalence in symptom control when switching between formulations
- Splitting Vyvanse doses (the medication is designed for once-daily dosing) 1
- Taking Vyvanse late in the day, which may exacerbate insomnia
- Failing to account for differences in onset and duration when evaluating treatment response
The 70mg Vyvanse dose provides the most comparable daily amphetamine exposure to 40mg total daily Adderall IR, while offering the advantage of once-daily dosing.