What is the appropriate starting dose and titration schedule of Vyvanse (lisdexamfetamine) for an 18‑year‑old (18 years 8 months) patient weighing 330 lb with ADHD?

Vyvanse Dosing for an 18-Year-Old Weighing 330 lb

Starting Dose and Titration

For an 18-year-old patient weighing 330 lb (150 kg) with ADHD, initiate lisdexamfetamine (Vyvanse) at 30 mg once daily in the morning, then increase by 10–20 mg at weekly intervals until optimal symptom control is achieved, up to a maximum of 70 mg daily. 1

• The FDA-approved starting dose for adults is 30 mg once daily, administered in the early morning 1, 2
• Titration should proceed in 10 mg increments at approximately weekly intervals 2, 1
• The maximum approved dose is 70 mg daily 1, 3
• Weight-based dosing is not used for lisdexamfetamine; systematic titration to the lowest effective dose that controls symptoms is the standard approach 3

Rationale for Standard Dosing Regardless of Weight

• Stimulant response is not correlated with body weight or height; approximately 70% of patients achieve optimal response when systematic dose-titration protocols are applied 3
• The 330 lb body weight does not justify starting at a higher dose or exceeding the 70 mg maximum 3, 1
• Clinical trials establishing lisdexamfetamine's efficacy used the 30–70 mg range in adults regardless of weight 1, 4

Monitoring During Titration

• Measure blood pressure and pulse at baseline and at each dose adjustment visit 3, 2
• Use standardized ADHD rating scales (such as ADHD-RS-IV) weekly during titration to objectively assess symptom response 2, 5
• Track height and weight at each visit, although growth effects are primarily relevant in pediatric populations 2
• Assess sleep quality and appetite changes, as these are the most common dose-limiting adverse effects 3, 6

Expected Timeline and Efficacy

• Lisdexamfetamine demonstrates efficacy within 1.5 hours post-dose and maintains effect through 13–14 hours 7, 1
• Stimulants achieve a 70–80% response rate when properly titrated 3, 4
• Full dose optimization typically requires 4 weeks 6, 7

Common Adverse Effects

• The most frequent treatment-emergent adverse events are decreased appetite (47–49%), insomnia (13–27%), headache (6–17%), irritability (9–16%), and weight decrease (18%) 6, 7
• These adverse effects are highest in the first 4–12 weeks and tend to decrease over time 6
• Median time to first onset: decreased appetite 13.5 days, insomnia 17 days, headache 22 days 6

Safety Considerations

• Lisdexamfetamine is contraindicated in patients with symptomatic cardiovascular disease, uncontrolled hypertension, or concurrent MAO inhibitor use 3
• The prodrug formulation provides lower abuse potential compared to immediate-release amphetamines, which is relevant for long-term management 2, 8
• Mean increases in vital signs at long-term assessment: pulse +7 bpm, systolic BP +3.4 mmHg, diastolic BP +3.2 mmHg 6

If Inadequate Response at Maximum Dose

• If symptoms remain uncontrolled at 70 mg daily after 4 weeks, consider switching to methylphenidate-class stimulants rather than exceeding the maximum dose 3, 5
• Approximately 40% of patients respond preferentially to one stimulant class over the other 3
• Verify medication adherence and assess for untreated comorbid conditions (anxiety, depression) that may masquerade as treatment failure 3