The P-I-E-N-O Parkinsn's List Drug Database
dextroamphetamine / DexedrineTM
STIMULANT :Amphetamine:
HIGH RISK
Description: Dextroamphetamine is an orally administered central nervous system agent. Dextroamphetamine is the d-isomer of amphetamine. Dextroamphetamine has greater CNS-stimulating activity than epinephrine or other catecholamines. Clinical uses of dextroamphetamine include the treatment of narcolepsy and as an adjunct in the treatment of attention-deficit disorder. It has also been used in management of obesity but this use is controversial. Dextroamphetamine and other amphetamines are DEA schedule II controlled substances. Dextroamphetamine was approved by the FDA in 1958.
Mechanism of Action: The predominant mechanism of dextroamphetamine's CNS effects is to stimulate the release of several biogenic amines from storage sites in the nerve terminal. Each molecule of amphetamine that is taken up by the nerve terminal displaces one molecule of neurotransmitter. At typical doses, amphetamines stimulate the release of norepinephrine. This action accounts for the general stimulation and anorectic effects of amphetamine. At higher doses, dopamine is released from its storage sites accounting for some of the behavioral changes seen with amphetamine. It is thought that the release of dopamine is responsible for the reinforcing properties of amphetamine. At still higher doses, amphetamine stimulates the release of 5-hydroxytryptamine (5-HT). It is this neurotransmitter that is thought to explain the overt psychotic behavior associated with amphetamine excess. Finally, amphetamine may act as a direct agonist on central 5-HT receptors. Thus, amphetamine is both a direct and an indirect stimulant. Indirect agonists are associated with tachyphylaxis due to the ever-decreasing supply of endogenous neurotransmitter than can be displaced from the nerve ending. Amphetamines may also inhibit monoamine oxidase, but this is a minor action.
The primary sites of activity in the CNS appear to be in the cerebral cortex and the reticular activating system. Amphetamine-induced CNS stimulation produces a decreased sense of fatigue, an increase in motor activity and mental alertness, mild euphoria, and brighter spirits. These effects are believed to be due to stimulation of norepinephrine release from central noradrenergic neurons. Lithium may offset amphetamine-induced euphoria. Of the two isomers of amphetamine, dextroamphetamine appears to have greater CNS stimulation.
In the periphery, the actions of amphetamines are believed to occur through release of noradrenaline from the adrenergic nerve terminals and by a direct stimulant action on ›-and œ-receptors. These actions produce respiratory stimulation, a pressor response, mydriasis, bronchodilation, and contraction of the bladder sphincter. The effect of amphetamines on GI tract motility is unpredictable.
In treating children with attention-deficit hyperactivity disorder, amphetamines produce a calming effect. This action of amphetamines results in a decrease in hyperactivity and an increase in the child's attention span.
Amphetamines seem to exert an anorexogenic effect. As a result of these effects, weight decreases. This agent is useful as an adjunct to decreased caloric intake in the treatment of obesity. The anorexogenic effect is postulated to be secondary to CNS stimulation and a decrease in the acuity of smell and taste. Amphetamines do not seem to alter the basal metabolic rate or nitrogen excretion.
Pharmacokinetics: Dextroamphetamine is readily absorbed from the GI tract following oral administration and is distributed to most body tissues. High concentrations are found in the CNS. Metabolism occurs in the liver. Excretion is via the kidney and is affected by pH, with more rapid excretion occurring in acidic urine and slower excretion occurring in alkaline urine. The plasma half-life is 6-8 hours in children and 10-12 hours in adults.
CONTRAINDICATIONS/PRECAUTIONS: Dextroamphetamine should be used with caution in the elderly and in patients with agitation, substance abuse, psychosis, suicidal ideation, or homicidal ideation.
Dextroamphetamine is contraindicated in patients with advanced arteriosclerosis, symptomatic cardiac disease, glaucoma, hypertension, hyperthyroidism, or Tourette's syndrome because it can exacerbate these conditions.
Dextroamphetamine is classified as pregnancy category C. Potential risks of dextroamphetamine use during pregnancy or breast-feeding are probably greater than the benefits; it should be used with great caution in these patients.
Dextroamphetamine should not be used as an anorexic agent in children under 12.
Dextroamphetamine should not be used within 2 weeks following discontinuation of a monoamine oxidase inhibitor because dextroamphetamine metabolism can be slowed, resulting in increased effects.
DRUG INTERACTIONS: Urinary acidifiers, such as ammonium chloride, reduce the tubular reabsorption of dextroamphetamine. As a result, dextroamphetamine clearance is accelerated and the duration of effect is reduced.
Dextroamphetamine can increase the sensitivity of the heart to the effects of inhalation anesthetics.
Dextroamphetamine potentiates the cardiovascular effects of tricyclic antidepressants by stimulating the release of noradrenaline. The drugs can be used concurrently, but close monitoring is necessary and doses may have to be adjusted.
Dextroamphetamine can cause hyperglycemia. Concurrent use with oral hypoglycemics and insulin may require dosage adjustments of the hypoglycemic agent. This represents a pharmacodynamic interaction and not a pharmacokinetic one.
Dextroamphetamine decreases the hypotensive effects of antihypertensive agents and diuretics. This represents a pharmacodynamic interaction and not a pharmacokinetic one.
Due to the risk of unopposed ›-adrenergic activity, dextroamphetamine should be used cautiously with œ-blockers including ophthalmic œ-blocker preparations.
Concurrent use of dextroamphetamine with other sympathomimetics can result in excessive CNS stimulation. Dextroamphetamine also can sensitize the myocardium to the effects of other sympathomimetics and cardiac glycosides, which can result in cardiac arrhythmias.
Dextroamphetamine causes delayed intestinal absorption of ethosuximide, phenobarbital, and phenytoin.
Haloperidol, loxapine, molindone, phenothiazines, pimozide, and thioxanthines inhibit the central stimulating effects of dextroamphetamine by producing ›-adrenergic blockade.
Levodopa increases the risk of developing dextroamphetamine-induced cardiac arrhythmias; the dose of dextroamphetamine should be reduced.
Lithium antagonizes the central stimulating effects of dextroamphetamine.
Concurrent use dextroamphetamine and meperidine is not recommended because hypotension, severe respiratory depression, coma, convulsions, vascular collapse, and death can occur. Dextroamphetamine also potentiates the analgesic effect of meperidine.
Intrathecal administration of metrizamide can increase the risk of developing dextroamphetamine-induced seizures. Amphetamines should be discontinued at least 48 hours before and 24 hours after myelography.
Dextroamphetamine prolongs and intensifies cardiac stimulation and vasopressor effects of MAOIs (including furazolidone, procarbazine, and selegiline). Amphetamines should not be administered during or within 14 days following the administration of MAOIs.
Overdosage of propoxyphene can potentiate the central stimulant effects of dextroamphetamine and other amphetamines to the extent that fatal convulsions can occur.
An increase in the effects of either dextroamphetamine or thyroid hormones can occur when these agents are used concurrently.
ADVERSE REACTIONS: Adverse reactions to dextroamphetamine can be serious. Those requiring medical attention include: cardiac arrhythmias and angina, severe CNS stimulation, Tourette's syndrome, and hyperthermia. During prolonged use of high doses, the following adverse reactions can occur: cardiomyopathy, palpitations, hypertension, or psychosis. Other side effects not usually requiring medical attention include: blurred vision, libido increase, diarrhea, weight loss, dizziness, lightheadedness, headache, sinus tachycardia, diaphoresis, and tremor.
Abrupt discontinuation of dextroamphetamine therapy can cause a withdrawal syndrome manifested as depression, nausea/vomiting, abdominal pain or cramps, constipation, or anorexia.
PATIENT INFORMATION:
What do dextroamphetamine tablets do?
Dextroamphetamine (DexedrineTM ) is a stimulant that can increase or stimulate some brain activity. It can improve attention span, concentration, and emotional control, while reducing restless or overactive behavior. Dextroamphetamine treats attention-deficit hyperactivity disorder in children. It can also help adults who have a condition called narcolepsy, an illness that makes you unable to stay awake. Federal law prohibits the transfer of dextroamphetamine to any person other than the patient for whom it was prescribed. Do not share this medicine with anyone else. Generic dextroamphetamine tablets are available.
What should my doctor or pharmacist know before I take dextroamphetamine?
They need to know if you have any of these conditions:
How should I take this medicine?
Take dextroamphetamine tablets by mouth. Follow the directions on the prescription label. Swallow the tablets with a drink of water. Take your last dose at least 6 hours before bedtime. Do not take your medicine more often than directed. Do not stop taking except on your doctor's advice.
Special precautions for use in children:
This medicine is not for use in children under 3 years old. It is only for children under 12 years old who have attention-deficit hyperactivity disorder.
What if I miss a dose?
If you miss a dose, take it as soon as you can. If it is almost time for your next dose, take only that dose. Do not take double or extra doses.
What other medicines can interact with dextroamphetamine?
Tell your doctor or pharmacist: about all other medicines you are taking, including non-prescription medicines; if you are a frequent user of drinks with caffeine or alcohol; if you smoke; or if you use illegal drugs. These may affect the way your medicine works. Check before stopping or starting any of your medicines.
What side effects may I notice from taking dextroamphetamine?
Serious side effects with dextroamphetamine include:
Call your doctor as soon as you can if you get any of these side effects.
Minor side effects with dextroamphetamine include:
Let your doctor know about these side effects if they do not go away or if they annoy you.
What do I need to watch for while I take dextroamphetamine?
Visit your doctor for regular checks on your progress. Dextroamphetamine is not for long-term use. Tell your doctor if this medicine loses its effects, or if you feel you need to take more than the prescribed amount. Do not change the dosage without advice from your doctor. If you suddenly stop taking dextroamphetamine you may get some unpleasant withdrawal effects. Ask your doctor for advice before you stop taking it.
If you are going to have surgery, tell your doctor or dentist that you are taking dextroamphetamine.
Do not take dextroamphetamine within 6 hours of bedtime. It can keep you from getting to sleep.
Do not take dextroamphetamine with other non-prescription medicines, especially cold and allergy medicines, without asking your doctor or pharmacist for advice.
Dextroamphetamine can hide signs that you are tired, reduce your coordination, or make you dizzy. Do not drive, use machinery, or do anything that needs mental alertness until you know how dextroamphetamine affects you.
Where can I keep my medicine?
Keep out of the reach of children in a container that small children cannot open.
Store at room temperature between 15 and 30C (59 and 86F). Keep container tightly closed. Throw away any unused medicine after the expiration date
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