Dexamphetamine is a member of the drug class Psychostimulants. It affects the nervous system and is used (sparingly) in
the treatment of patients with disorders such as Narcolepsy. It is known as Dextroamphetamine in the USA and is sold under the brand name Dexadrine (thanks to etoile for the info). The following info is taken from the Product information
section of a pharmaceutical database used widely by clinicians in Australia.
Dexamphetamine Tablets contain the dextro isomer of d,l-
amphetamine sulfate.
Chemical name:
(S)-alpha-methylphenethylamine sulfate. Molecular formula: (C19H13N)2H2S04. MW: 368.5 It is
soluble approximately 1:10 in
water, 1:500 in
alcohol 95% and readily soluble in
acids.
Actions
Sympathomimetic amine of the amphetamine group.
Pharmacology
Amphetamines are noncatecholamine, sympathomimetic amines with CNS stimulant activity. Dexamphetamine stimulates both
alpha- and beta-adrenergic receptors. Peripheral actions include elevation of systolic and diastolic blood pressures
and weak bronchodilator and respiratory stimulant actions. It causes pronounced stimulation of the central cortex and
the respiratory and vasomotor centres. It increases motor activity, mental alertness and wakefulness, and produces
euphoria.
The exact mechanism of action has not been established, however in animals, amphetamines facilitate the action of dopamine
and noradrenaline by blocking reuptake from the synapse, inhibit the action of monoamine oxidase (MAO), and facilitate the
release of catecholamines. There is no specific evidence which clearly establishes the mechanism whereby amphetamines
produce mental and behavioural effects in children, nor conclusive evidence regarding how these effects relate to the
condition of the central nervous system.
Tolerance and dependence of the amphetamine type develop on repeated administration.
Pharmacokinetics
Amphetamines are rapidly absorbed from the gastrointestinal tract reaching peak levels in approximately two hours
postadministration and have an apparent volume of distribution of 2 to 3L/kg bodyweight. Dexamphetamine is concentrated in
the brain, lung and kidneys. 30 to 40% is metabolised by the liver, and the hydroxylated metabolite may be responsible for
the psychotic effect; the remainder (60 to 70%) is excreted directly by the kidneys. The approximate plasma half-life is
10.25 hours, however excretion of dexamphetamine is enhanced in an acid urine and slowed in an alkaline urine. The half-life
is 16 to 31 hours in a urine with a pH of more than 7.5 and falls to 6 to 8 hours when the urinary pH is 5.0 or less. The
average urinary recovery is 45% in 48 hours.
Warnings
Because of the liability for abuse, drugs of the amphetamine type are subject to special restrictions on their
availability. Prescriptions of this substance may require validation by State or Territory Health Departments or
Commissions.
Drug abuse potenital.
Amphetamines have a high potential for drug abuse. Care should be exercised in the selection of patients for amphetamine
therapy and prescription size should be limited to that required to achieve the therapeutic goal. Patients should be
cautioned against increasing the recommended dosage. Should psychological dependence occur, gradual withdrawal of the
medication is recommended.
Abrupt cessation following prolonged high dosage results in extreme fatigue and mental depression; changes have also
been noted on the sleep electroencephalogram (EEG). Manifestations of chronic intoxication with amphetamines include
severe dermatoses, marked insomnia, irritability, hyperactivity and personality changes. The most severe manifestation
of chronic intoxication is psychosis, often clinically indistinguishable from schizophrenia.
Adverse Reactions
- Cardiovascular.
Palpitations, tachycardia, elevation of blood pressure and some reports of cardiomyopathy associated with chronic
amphetamine use.
- Central nervous system.
Psychotic episodes at recommended doses (uncommon), overstimulation, restlessness, dizziness, insomnia, dyskinesia, tremor,
headache, exacerbation of motor and phonic tics and Tourette syndrome.
- Gastrointestinal.
Mouth dryness, unpleasant taste, diarrhoea, constipation, other gastrointestinal disturbances.
- Allergic.
Urticaria.
- Endocrine.
Impotence, changes in libido.
- Other.
Anorexia and weight loss.
Overdosage
Individual response to amphetamines varies widely. While toxic symptoms occasionally occur as an idiosyncrasy at doses as
low as 2 mg, they are uncommon with doses of less than 15 mg. Doses of 30 mg can produce severe reactions, yet doses of 400
to 500 mg are not necessarily fatal.
Symptoms.
Symptoms include dilated and reactive pupils, shallow rapid respiration, rhabdomyolysis, fever, chills, sweating,
hyperactive tendon reflexes. Central effects may include restlessness, aggressiveness, anxiety, confusion, delirium,
hallucinations, panic attacks and suicidal or homicidal tendencies. The stimulant effect is usually followed by
depression, lethargy, exhaustion. Cardiovascular effects may include anginal pain, extrasystoles, and other arrhythmias,
flushing, headache, hypertension, or hypotension, pallor, palpitations, tachycardia. Circulatory collapse and syncope may
occur. Gastrointestinal effects include nausea, vomiting, diarrhoea and abdominal cramps. Fatal poisoning is usually
preceded by convulsions and coma.
Drug abuse and dependence
.
Amphetamines have been extensively abused. Tolerance, extreme psychological dependence and severe social disability have
occurred. There are reports of patients who have increased the dosage to many times that recommended. Abrupt cessation
following prolonged high dosage results in extreme fatigue and mental depression; changes are also noted on sleep EEG.
Manifestations of chronic intoxication with amphetamines include restlessness, tremor, hyperreflexia, rhabdomyolysis,
rapid respiration, hyperpyrexia, confusion, aggression, hallucinations, panic states, severe dermatoses, marked insomnia,
irritability, hyperactivity and personality changes. The most severe manifestation of chronic intoxication is psychosis,
often clinically indistinguishable from schizophrenia. This is uncommon with oral amphetamines.
Source: MIMS Pharmeceutical Database 01/02/2003