Dexamfetamine

Product Description

Clinical Monograph: Dexamfetamine

1. Classification and Chemical Overview

Dexamfetamine is the dextro-isomer of racemic amphetamine, belonging to the phenethylamine class of centrally acting sympathomimetic agents. Chemically designated as $(2S)$-1-phenylpropan-2-amine sulfate, it represents the pharmacologically active enantiomer of amphetamine. Under the Anatomical Therapeutic Chemical (ATC) system, dexamfetamine is indexed under N06BA02.

• Product Context: Formulated as immediate-release oral tablets (typically 5 mg) or oral liquid solutions. Unlike lisdexamfetamine (which is a prodrug), dexamfetamine is active immediately upon ingestion.

• Controlled Status: Strictly regulated as a Prescription Only Medicine (POM) and a Schedule II Controlled Substance (or Class B / Schedule 2 Controlled Drug internationally) due to its high potential for abuse, psychological dependence, and misuse liability.

2. Mechanism of Action and Pharmacodynamics

Dexamfetamine exerts its therapeutic and stimulant effects by modulating central monoamine neurotransmission:

• Presynaptic Release: Enters presynaptic monoamine nerve terminals via active transport (DAT and NET), where it induces the robust, non-exocytotic release of dopamine (DA) and norepinephrine (NE) from storage vesicles into the cytoplasm and subsequently into the synaptic cleft.

• Reuptake Inhibition: Binds to and inhibits monoamine transporters (DAT, NET, and to a lesser extent, SERT), preventing the clearance of neurotransmitters from the synapse.

• MAO Inhibition (Weak): Weakly inhibits monoamine oxidase (MAO) enzymes at high concentrations.

• Pharmacodynamic Profile: Amplified catecholamine signaling within the prefrontal cortex and striatum improves sustained attention, impulse control, motor hyperactivity, and wakefulness in narcolepsy.

3. Approved Clinical Indications and Dosing Scope

Licensing for dexamfetamine includes:

• Attention Deficit Hyperactivity Disorder (ADHD): Treatment of ADHD in children (aged 3 years and older) and adults as part of a comprehensive management program.

• Narcolepsy: Management of excessive daytime sleepiness associated with narcolepsy.

Dosing & Administration Regimen:

• Individualized Titration: Initiated at low doses (e.g., 5 mg once or twice daily) and titrated upward gradually by small increments at weekly intervals based on clinical response and tolerability.

• Timing of Doses: Administered in divided doses throughout the day, with the first dose taken upon awakening. Subsequent doses are spaced at intervals of 4 to 6 hours. Avoid late afternoon or evening administration to prevent severe, prolonged insomnia.

4. Pharmacokinetic Profile and Metabolic Fate

• Absorption: Rapidly and completely absorbed from the gastrointestinal tract following oral ingestion. Peak plasma concentrations ($C_{max}$) are achieved within 1 to 3 hours ($T_{max}$) for immediate-release formulations.

• Distribution: Readily crosses the blood-brain barrier and placenta; distributes extensively into body tissues. Plasma protein binding is low (~15% to 20%).

• Biotransformation: Metabolized in the liver primarily via aromatic and aliphatic hydroxylation, $N$-dealkylation, and deamination. Major pathways involve CYP2D6 to yield active and inactive hydroxylated metabolites (such as 4-hydroxyamphetamine and norephedrine).

• Elimination: Excreted predominantly via the kidneys in urine as unchanged parent drug and metabolites. Urinary elimination is heavily dependent on urinary pH: acidic urine accelerates renal clearance, whereas alkaline urine prolongs the elimination half-life. The terminal elimination half-life averages 10 to 12 hours in adults.

5. Physiological Effects and Adverse Event Spectrum

Dexamfetamine stimulates the sympathetic nervous system, increasing heart rate, elevating blood pressure, dilating pupils, and suppressing appetite.

Adverse Drug Reaction Spectrum

• Very Common ($\ge 1/10$): Decreased appetite, weight loss, insomnia, dry mouth, headache, emotional lability, tachycardia, abdominal pain.

• Common ($\ge 1/100$ to $<1/10$): Palpitations, anxiety, restlessness, dizziness, tremor, dysgeusia, constipation, diarrhea, hyperhidrosis, bruxism, growth velocity suppression in pediatric patients.

• Uncommon ($\ge 1/1,000$ to $<1/100$): Hypertension, vision blurred, rash, libido changes, psychomotor hyperactivity, depression.

• Rare / Severe (<1/1,000): Psychotic episodes, visual and tactile hallucinations, cardiomyopathy (with chronic high-dose misuse), seizures, cerebrovascular accidents, myocardial infarction, sudden cardiac death in vulnerable individuals.

6. Contraindications, Drug Interactions, and Clinical Precautions

Contraindications

• Known hypersensitivity to amphetamine products or formulation excipients.

• Concomitant use with Monoamine Oxidase Inhibitors (MAOIs) or within 14 days of their cessation (risk of life-threatening hypertensive crisis).

• Advanced arteriosclerosis, symptomatic cardiovascular disease, moderate-to-severe hypertension, or structural cardiac abnormalities.

• Hyperthyroidism, glaucoma, or history of advanced agitated states.

• History of active drug abuse or substance use disorder.

Key Drug Interactions

• Monoamine Oxidase Inhibitors (MAOIs): Concurrent administration triggers severe hypertensive crises and dangerous hyperthermia.

• Serotonergic Agents (SSRIs, SNRIs): Co-administration elevates the risk of serotonin syndrome due to enhanced monoaminergic activity.

• Acidifying & Alkalinizing Agents: Gastrointestinal and urinary acidifiers (e.g., ascorbic acid, ammonium chloride) accelerate renal clearance and reduce efficacy, whereas urinary alkalinizers (e.g., sodium bicarbonate) prolong half-life and increase systemic exposure.

• Antihypertensives: Stimulants can antagonize the blood pressure-lowering effects of antihypertensive medications.

Clinical Precautions and Monitoring

• Boxed Warning (Abuse, Misuse, and Dependence): CNS stimulants have a high potential for abuse and dependence. Assess clinical risk prior to prescribing and monitor patients regularly for signs of misuse, diversion, or dose escalation.

• Cardiovascular Evaluation: Evaluate cardiac status prior to treatment. Monitor blood pressure and heart rate regularly during therapy, particularly in patients with underlying cardiovascular conditions.

• Growth Suppression: Long-term stimulant use in pediatric patients can be associated with temporary suppression of weight gain and linear growth velocity; monitor height and weight periodically

Additional Information