Dextroamphetamine (Dexedrine)

Stimulant - Central Nervous System Stimulant

Overview

Dextroamphetamine, marketed as Dexedrine, is a potent central nervous system stimulant used primarily for Attention Deficit Hyperactivity Disorder (ADHD) and narcolepsy. As the dextrorotatory isomer of amphetamine, it is more active than its racemic counterpart, providing enhanced focus and impulse control. Dextroamphetamine is a Schedule II controlled substance due to its high potential for abuse, requiring careful monitoring for cardiovascular effects and misuse.

Mechanism of Action

Dextroamphetamine increases the release of dopamine and norepinephrine by reversing the dopamine transporter (DAT) and norepinephrine transporter (NET), while also inhibiting their reuptake. It also inhibits monoamine oxidase (MAO), further increasing catecholamine levels. This amplifies dopaminergic and noradrenergic activity in the prefrontal cortex, enhancing attention, alertness, and executive function.

Indications

  • Attention Deficit Hyperactivity Disorder (ADHD): Approved for children (3 years and older) and adults.
  • Narcolepsy: Approved for ages 6 years and older.
  • Treatment-Resistant Depression: Used as an adjunct in patients with fatigue or apathy.
  • Obesity: Historically used for short-term weight loss (not recommended due to abuse potential).
  • Cognitive Enhancement: Used in fatigue states post-chemotherapy or in neurological conditions.

Dosing and Administration

Indication Starting Dose Therapeutic Range Maximum Dose
ADHD (Children 3-5 years) 2.5 mg/day 2.5-40 mg/day in divided doses 40 mg/day
ADHD (Children 6 years and older, Adults) 5 mg once or twice daily 5-40 mg/day in divided doses 40 mg/day
Narcolepsy 10 mg/day 10-60 mg/day in divided doses 60 mg/day
  • Elderly: Use with caution; start at lower doses due to cardiovascular risks.
  • Hepatic Impairment: No specific adjustment; monitor for toxicity.
  • Renal Impairment: No adjustment needed; use caution in severe impairment.
  • Pregnancy: Category C; potential for fetal harm; use only if benefits outweigh risks.
  • Breastfeeding: Excreted in breast milk; monitor infant for agitation or poor weight gain.
Clinical Pearl: Dextroamphetamine should be taken early in the day to avoid insomnia. Avoid late afternoon doses, especially with IR formulations.

Pharmacokinetics

Parameter Details
Absorption Rapid; peak plasma levels in 3 hours (IR), 8 hours (ER).
Metabolism Hepatic via CYP2D6; some metabolism via aromatic hydroxylation.
Half-Life 10-13 hours in adults; 9-11 hours in children.
Excretion Urine (70-80%, pH-dependent); 30% as unchanged drug.
Clinical Pearl: Urinary pH affects excretion; acidic urine increases clearance, while alkaline urine prolongs half-life. Avoid urinary alkalinizers (e.g., sodium bicarbonate) to prevent accumulation.

Side Effects

  • Central Nervous System: Insomnia (15-20%), anxiety (10%), irritability (8%), headache (6%).
  • Gastrointestinal: Decreased appetite (30%), nausea (5%), dry mouth (7%).
  • Cardiovascular: Increased heart rate (6%), increased blood pressure (4%).
  • Other: Weight loss (10-15%), tremor (3%).

Data from clinical trials (Shire, 2023).

  • Cardiovascular Events: Risk of hypertension, tachycardia; rare sudden death in patients with cardiac abnormalities.
  • Psychiatric Effects: Risk of psychosis or mania, especially at high doses.
  • Dependence/Abuse: High abuse potential; Schedule II controlled substance.
  • Growth Suppression: May affect growth in children; monitor closely.
  • Seizures: May lower seizure threshold; use cautiously in epilepsy.
Clinical Pearl: Monitor for signs of aggression or mood changes, especially in patients with a history of psychiatric disorders. Weight loss may be more pronounced than with methylphenidate.

Interactions

  • MAOIs (e.g., phenelzine): Risk of hypertensive crisis; contraindicated within 14 days.
  • Antihypertensives: May reduce efficacy of BP medications; monitor closely.
  • Acidifying Agents (e.g., ascorbic acid): Increase excretion; may reduce efficacy.
  • Alkalinizing Agents (e.g., sodium bicarbonate): Decrease excretion; may increase toxicity.
  • Alcohol: May exacerbate CNS effects; avoid use.
Clinical Pearl: Dextroamphetamine’s effects on BP and HR may be more pronounced than methylphenidate; avoid combining with other stimulants (e.g., caffeine) to minimize cardiovascular risks.

Contraindications and Warnings

  • Hypersensitivity to amphetamines.
  • Use of MAOIs within 14 days.
  • Severe hypertension, heart failure, or arrhythmias.
  • Hyperthyroidism or glaucoma.
  • Cardiovascular Risk: FDA warning for sudden death in patients with cardiac conditions; baseline ECG recommended.
  • Psychiatric Symptoms: May exacerbate psychosis or mania; screen for bipolar disorder.
  • Abuse Potential: High risk; monitor for misuse and diversion.
  • Seizure Risk: May lower seizure threshold; use cautiously in epilepsy.
  • Peripheral Vasculopathy: Risk of Raynaud’s phenomenon; monitor extremities.

Evidence and Guidelines

  • ADHD: 75-80% response rate in children; comparable efficacy to methylphenidate (Arnold et al., 2004).
  • Narcolepsy: Reduces daytime sleepiness by 60-70% (Mitler et al., 1994).
  • Cardiovascular Safety: Increases BP by 3-5 mmHg, HR by 4-8 bpm; no significant QT prolongation (FDA, 2011).
  • AAP (2019): Alternative to methylphenidate for ADHD; monitor for abuse potential.
  • NICE (2018): Recommended for ADHD; prefer ER formulations to reduce abuse risk.
  • FDA Labeling: Warning for cardiovascular risks and dependence; baseline cardiac evaluation advised.

Monitoring Parameters

  • Cardiovascular: Monitor BP and HR at baseline and monthly; ECG if cardiac history.
  • Psychiatric Symptoms: Screen for psychosis or mania, especially in first month.
  • Growth: Monitor height and weight in children every 3-6 months.
  • Abuse Potential: Assess for misuse, especially in patients with substance use history.
  • Seizures: Monitor for seizure activity in patients with epilepsy.

Patient Education

  • What to Expect: Improved focus and alertness within 30-60 minutes; effects last 4-6 hours (IR) or 10-12 hours (ER).
  • Managing Side Effects: Take early in the day to avoid insomnia; eat frequent small meals to manage appetite loss.
  • When to Seek Help: Contact your doctor for chest pain, irregular heartbeat, hallucinations, or signs of misuse.
  • Controlled Substance: Do not share; store securely to prevent diversion.