Will Vyvanse (lisdexamfetamine) cause the same lockjaw effect as Adderall IR (amphetamine) in a patient with a history of severe lockjaw on Adderall IR?

Vyvanse May Cause Less Severe Lockjaw Than Adderall IR

Switching from Adderall IR to Vyvanse is likely to reduce the severity of lockjaw (bruxism) but may not eliminate it completely, as both medications contain amphetamine as their active component. 1, 2

Pharmacological Differences Between Adderall IR and Vyvanse

Vyvanse (lisdexamfetamine) differs from Adderall IR (mixed amphetamine salts) in several important ways:

• Vyvanse is a prodrug that must be metabolized in the bloodstream to its active form, d-amphetamine 2, 3
• This metabolism results in a more gradual onset of action compared to Adderall IR 3
• Vyvanse has a 0.6 ± 0.6 hour longer lag time and reaches peak levels 1.1 ± 1.5 hours later than immediate-release d-amphetamine 3
• Vyvanse provides a more consistent drug level over 12 hours versus the more rapid peaks and troughs of Adderall IR 4, 5

Why Vyvanse May Reduce Lockjaw

The gradual release profile of Vyvanse may reduce the severity of side effects like lockjaw for several reasons:

1. The slower onset and more consistent blood levels may reduce peak-related side effects 3, 5
2. The absence of sudden spikes in amphetamine concentration may decrease the intensity of jaw clenching 3
3. The extended-release mechanism provides more stable dopamine and norepinephrine levels throughout the day 2, 5

Management Approach for Stimulant-Induced Lockjaw

If lockjaw persists even with Vyvanse, consider these strategies:

• Dose adjustment: Lower doses may reduce side effects while maintaining efficacy 1
• Timing modification: Administering the medication earlier in the day may reduce nighttime bruxism 1
• Alternative medications: If lockjaw remains severe, consider non-stimulant options:
  • Atomoxetine (Strattera) - a norepinephrine reuptake inhibitor 1
  • Viloxazine, Guanfacine XR, or Clonidine XR 1
  • Bupropion (off-label) 1

Monitoring Recommendations

When switching from Adderall IR to Vyvanse:

• Schedule follow-up within 2-4 weeks to assess lockjaw symptoms and medication efficacy 1
• Monitor for other common side effects: decreased appetite, sleep disturbances, irritability 1
• Check vital signs including heart rate and blood pressure 1
• Use standardized rating scales to evaluate ADHD symptom control 1

Important Considerations

• Vyvanse and d-amphetamine produce similar peak subjective effects and cardiovascular responses, despite differences in onset timing 3
• The total amphetamine exposure (AUC) is equivalent between Vyvanse and equivalent doses of d-amphetamine 3
• Common starting dose for Vyvanse is 30mg daily, which can be titrated up to a maximum of 70mg daily based on response 5

Potential Pitfalls

• Assuming complete resolution of lockjaw with medication switch alone
• Overlooking the need for dose adjustment when switching between stimulant medications
• Failing to consider non-pharmacological approaches to managing bruxism (night guards, stress reduction techniques)
• Not recognizing that severe bruxism may indicate the need for a complete class switch to non-stimulant options