Amphetamines
GENERAL PRINCIPLES
Amphetamines and amphetamine derivatives are used medically in the treatment of attention-deficit hyperactivity disorderand to a lesser degree for narcolepsy and weight loss.
Both pharmaceutical and nonpharmaceutical amphetamines and amphetamine derivatives are used for recreational purposes.
Pathophysiology
Amphetamines induce the release of monoamine neurotransmitters (norepinephrine, serotonin, and dopamine) and inhibit their reuptake, creating an excitatory or sympathomimetic state.
Amphetamines with oxygen or halogen substitutions, such as methylenedioxymethamphetamine (MDMA, ecstasy), tend to have more serotonergic effects.
Methamphetamine is uniquely toxic and addictive. Its additional methyl group facilitates more rapid movement across the blood-brain barrier.
Methamphetamine (and to a lesser degree other amphetamines) also cause a direct vasculopathy.
DIAGNOSIS
Clinical Presentation
Amphetamine poisoning presents with the sympathomimetic toxidrome of tachycardia, hypertension, diaphoresis, hyperthermia, and mental status changes (ranging from anxiety to agitated delirium). This can cause end-organ damage including seizures, neurologic deficits from stroke or intracranial hemorrhage, or chest pain.
Methamphetamine (and other amphetamines) may cause psychiatric derangements, including mania and psychosis. Methamphetamine-induced psychosis may persist for weeks after cessation of exposure.
Diagnostic Testing
LABORATORIES
Urine drug testing is not useful in acute clinical management.
Have a low threshold to obtain a BMP, troponin, and/or creatinine kinase to evaluate for end-organ damage, including renal injury, myocardial ischemia, and rhabdomyolysis.
ELECTROCARDIOGRAPHY
Electrocardiography may demonstrate sinus tachycardia or ventricular dysrhythmias.
IMAGING
Imaging to evaluate for end-organ damage should be guided by the patient's complaints and physical examination.
๎ Obtain computed tomography of the brain in patients with significant mental status changes or headache to evaluate for intracranial hemorrhage.
๎ Obtain computed tomography angiogram of the chest in patients with chest pain that is clinically concerning for aortic dissection.
TREATMENT
The mainstay of treatment is benzodiazepines or other directly GABAergic sedatives, titrated to control of agitation and improvement of vital signs.
Patients presenting with predominantly psychiatric symptoms (psychosis or mania) may benefit from antipsychotics. 26
Intravenous fluid resuscitation is reasonable and is mandatory in cases of rhabdomyolysis.
Control of blood pressure and heart rate should be achieved by appropriate titration of benzodiazepines or other sedatives. When tight blood pressure control is required (e.g., aortic dissection, intracranial hemorrhage, acute MI), use agents that are rapidly titratable, such as nicardipine, clevidipine, or nitroglycerin.
Patients with hyperthermia require aggressive external cooling in addition to aggressive sedation. Paralysis with nondepolarizing neuromuscular blockers may be required in severe cases.