Elimination Half-Life of Dextroamphetamine
The elimination half-life of dextroamphetamine is approximately 11–12 hours in adults. 1, 2
Pharmacokinetic Parameters
The FDA-approved drug label reports a half-life of 11.75 hours following a 10 mg oral dose of dextroamphetamine sulfate in healthy volunteers. 2
The American College of Clinical Pharmacology states the plasma half-life is 11–11.75 hours for dextroamphetamine, providing the most authoritative reference range. 1
Peak plasma concentration (Cmax) occurs within 1–3 hours after oral administration, with the FDA label specifically documenting an average peak of 33.2 ng/mL at approximately 3 hours post-dose. 1, 2
Age-Related Variations
Children aged 4–5 years metabolize stimulants more slowly than older children and adults, requiring lower starting doses and potentially exhibiting longer half-lives. 1
In pediatric populations (ages 6–16), one study documented a shorter apparent elimination half-life of 6.8 ± 0.5 hours, though this may reflect differences in study methodology or developmental pharmacokinetics. 3
In acute stroke patients (ages 37–84), the median terminal half-life was 14.3 hours (interquartile range 11.9–16.9), suggesting that advanced age or comorbid conditions may prolong elimination. 4
Clinical Implications of the Half-Life
Despite the 11–12 hour elimination half-life, immediate-release formulations provide only 3–4 hours of clinical effect because therapeutic response correlates with peak dopaminergic activity rather than plasma concentration alone. 1
Extended-release formulations leverage the long half-life to provide 8+ hours of clinical action through modified delivery mechanisms that sustain peak concentrations. 1
The long elimination half-life explains why dextroamphetamine causes greater appetite suppression and sleep disturbance compared to methylphenidate, which has a shorter half-life of approximately 2–4 hours. 5
Metabolism and Excretion
Up to 80% of dextroamphetamine is excreted unchanged in urine, making renal function a critical determinant of drug clearance and half-life. 1
The FDA label documents an average urinary recovery of 38% within 48 hours, consistent with pH-dependent renal elimination. 2
Urinary pH significantly affects elimination: acidic urine (pH < 6) accelerates excretion and shortens half-life, while alkaline urine (pH > 7) prolongs it. 1
Comparison with Lisdexamfetamine (Prodrug)
Lisdexamfetamine itself has a very short half-life of 0.47 hours because it is rapidly converted to dextroamphetamine by red blood cell enzymes. 6
Once converted, the active d-amphetamine metabolite exhibits a half-life of 10–11.3 hours, nearly identical to immediate-release dextroamphetamine. 7, 6
The prodrug design of lisdexamfetamine provides 13–14 hours of therapeutic coverage despite the similar elimination half-life, due to rate-limited enzymatic conversion that sustains plasma levels. 7, 8
Practical Dosing Considerations
Twice-daily dosing (morning and noon) is standard for immediate-release dextroamphetamine to maintain therapeutic coverage throughout the school or work day. 5, 2
Late-day dosing should be avoided because the 11–12 hour half-life means significant plasma concentrations persist into the evening, causing insomnia. 1, 8
The long half-life allows once-daily dosing with extended-release formulations, eliminating the need for in-school administration and improving adherence. 7, 8