Pediatric emergency medicine trisk 3150 3150
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form of methamphetamine (“ice”) is associated with more striking and prolonged
alterations in CNS function. Children may be exposed to a myriad of dangerous
chemicals when living with adults who operate clandestine methamphetamine
laboratories.
Amphetamines have powerful CNS stimulant actions, in addition to peripheral
adrenergic actions. Unlike epinephrine, amphetamines are effective after oral
administration. However, they are often taken by injection and nasal insufflation.
The pharmacologic effects of amphetamines include increased blood pressure,
occasionally with a reflex slowing of heart rate though more commonly with
tachycardia, contraction of bladder sphincter, and dramatic CNS stimulation. Like
other indirect sympathomimetics, amphetamines act by releasing endogenous
biogenic amines from the presynaptic neurons. MDMA has more serotonergic
activity (associated with both increased release and decreased reuptake of
serotonin) which accounts for clinical effects and a toxicity profile that differ
from that of traditional amphetamines.
The therapeutic dose of dextroamphetamine in adolescents is typically 5 mg
three times daily. The toxic dose is variable but is rarely less than 15 mg. Severe
reactions have been reported at 30 mg, yet doses up to 400 to 500 mg may cause
only mild symptoms. Tolerance is striking, with chronic users taking 10 to 15 g
daily without apparent ill effects. The elimination half-life of the amphetamines is
about 3 hours, with much of the drug being excreted in the urine unchanged.
Timing of onset of symptoms and duration of clinical effects differs based on
route of exposure and the unique characteristics of the particular formulation or
amphetamine derivative.
Clinical Considerations
The psychic effect of amphetamines depends on the dose, mental state, and
personality of the drug user. In general, 10 to 30 mg cause wakefulness, alertness,
a decreased sense of fatigue, and an elevation of mood. Other behavioral changes
may include increased initiative, self-confidence, ability to concentrate, elation,
euphoria, increased motor and speech activity, and improved physical
performance in athletes. Prolonged use of large doses is followed by depression
and fatigue. Amphetamines have an appetite-suppressant effect through an action
on the lateral hypothalamic feeding center. However, tolerance to this effect also
develops; thereafter, the effect is insufficient to reduce weight for a sustained
period.
The acute toxic effects of amphetamine are usually extensions of its therapeutic
actions. The central effects induce euphoria, restlessness, dizziness, tremor,
