Caution is to be exercised in prescribing amphetamines for patients with even mild hypertension.
The least amount feasible should be prescribed or dispensed at one time in order to minimize the possibility of overdosage.
Amphetamines may impair the ability of the patient to engage in potentially hazardous activities such as operating machinery or vehicle; the patient should therefore be cautioned accordingly.
Circulation problems in fingers and toes [Peripheral vasculopathy, including Raynaud’s phenomenon]
- Instruct patients beginning treatment with amphetamine sulfate about the risk of peripheral vasculopathy, including Raynaud’s Phenomenon, and associated signs and symptoms: fingers or toes may feel numb, cool, painful, and/or may change color from pale, to blue, to red.
- Instruct patients to report to their physician any new numbness, pain, skin color change, or sensitivity to temperature in fingers or toes.
- Instruct patients to call their physician immediately with any signs of unexplained wounds appearing on fingers or toes while taking amphetamine sulfate.
- Further clinical evaluation (e.g., rheumatology referral) may be appropriate for certain patients.
Acidifying agents — Gastrointestinal acidifying agents (guanethidine, reserpine, glutamic acid HCl, ascorbic acid, fruit juices, etc.) lower absorption of amphetamines. Urinary acidifying agents (ammonium chloride, sodium acid phosphate, etc.) increase concentration of the ionized species of the amphetamine molecule, thereby increasing urinary excretion. Both groups of agents lower blood levels and efficacy of amphetamines.
Adrenergic blockers — Adrenergic blockers are inhibited by amphetamines.
Alkalinizing agents — Gastrointestinal alkalinizing agents (sodium bicarbonate, etc.) increase absorption of amphetamines. Urinary alkalinizing agents (acetazolamide, some thiazides) increase the concentration of the non-ionized species of the amphetamine molecule, thereby decreasing urinary excretion. Both groups of agents increase blood levels and therefore potentiate the action of amphetamines.
Antidepressants tricyclic — Amphetamines may enhance the activity of tricyclic or sympathomimetic agents; d-amphetamine with desipramine or protriptyline and possibly other tricyclics cause striking and sustained increases in the concentration of d- amphetamine in the brain; cardiovascular effects can be potentiated.
CYP2D6 Inhibitors — The concomitant use of amphetamine sulfate and CYP2D6 inhibitors may increase the exposure of amphetamine sulfate compared to the use of the drug alone and increase the risk of serotonin syndrome. Initiate with lower doses and monitor patients for signs and symptoms of serotonin syndrome particularly during amphetamine sulfate initiation and after a dosage increase. If serotonin syndrome occurs, discontinue amphetamine sulfate and the CYP2D6 inhibitor (see WARNING, OVERDOSAGE). Examples of CYP2D6 Inhibitors include paroxetine and fluoxetine (also serotonergic drugs), quinidine, ritonavir.
Serotonergic Drugs — The concomitant use of amphetamine sulfate and serotonergic drugs increases the risk of serotonin syndrome. Initiate with lower doses and monitor patients for signs and symptoms of serotonin syndrome, particularly during amphetamine sulfate initiation or dosage increase. If serotonin syndrome occurs, discontinue amphetamine sulfate and the concomitant serotonergic drug(s) (see WARNING and PRECAUTIONS). Examples of serotonergic drugs include selective serotonin reuptake inhibitors (SSRI), serotonin norepinephrine reuptake inhibitors (SNRI), triptans, tricyclic antidepressants, fentanyl, lithium, tramadol, tryptophan, buspirone, St. John’s Wort.
MAO inhibitors — MAOI antidepressants, as well as a metabolic of furazolidone, slow amphetamine metabolism. This slowing potentiates amphetamines, increasing their affect on the release of norepinephrine and other monoamines from adrenergic nerve endings; this can cause headaches and other signs of hypertensive crisis. A variety of neurological toxic effects and malignant hyperpyrexia can occur, sometimes with fatal results.
Antihistamines — Amphetamines may counteract the sedative effect of antihistamines.
Antihypertensives — Amphetamines may antagonize the hypotensive effects of antihypertensives.
Chlorpromazine — Chlorpromazine blocks dopamine and norepinephrine reuptake, thus inhibiting the central stimulant effects of amphetamine, and can be used to treat amphetamine poisoning.
Ethosuximide — Amphetamines may delay intestinal absorption of ethosuximide.
Haloperidol — Haloperidol blocks dopamine and norepinephrine reuptake, thus inhibiting the central stimulant effects of amphetamines.
Lithium carbonate — The antiobesity and stimulatory effects of amphetamines may be inhibited by lithium carbonate.
Meperidine — Amphetamines potentiate the analgesic effect of meperidine.
Methenamine therapy — Urinary excretion of amphetamines is increased, and efficacy is reduced by acidifying agents used in methenamine therapy.
Norepinephrine — Amphetamines enhance the adrenergic effect of norepinephrine.
Phenobarbital — Amphetamines may delay intestinal absorption of Phenobarbital. Co- administration of phenobarbital may produce a synergistic anticonvulsant action.
Phenytoin — Amphetamines may delay intestinal absorption of phenytoin; co- administration of phenytoin may produce a synergistic anticonvulsant action.
Propoxyphene — In cases of propoxyphene overdosage, amphetamine CNS stimulation is potentiated and fatal convulsions can occur.
Veratrum alkaloids — Amphetamines inhibit the hypotensive effect of veratrum alkaloids.
Drug/Laboratory Test interactions
Amphetamines can cause a significant elevation in plasma corticosteroid levels. This increase is greatest in the evening. Amphetamines may interfere with urinary steroid determinations.
Mutagenicity studies and long term studies in animals to determine the carcinogenic potential of amphetamine sulfate have not been performed.
Pregnancy Category C. Dextroamphetamine sulfate has been shown to have embryotoxic and teratogenic effects when administered to A/Jax mice and C57BL mice in doses approximately 41 times the maximum human dose. Embryotoxic effects were not seen in New Zealand white rabbits given the drug in doses 7 times the human dose nor in rats given 12.5 times the maximum human dose. There are no adequate and well-controlled studies in pregnant women. amphetamine sulfate should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
Infants born to mothers dependent on amphetamines have an increased risk of premature delivery and low birth weight. Also, these infants may experience symptoms of withdrawal as demonstrated by dysphoria, including agitation, and significant lassitude.
Amphetamines are excreted in human milk. Mothers taking amphetamines should be advised to refrain from nursing.
Long-term effects of amphetamines in children have not been well established.
Amphetamines are not recommended for use as anorectic agents in children under 12 years of age, or in children under 3 years of age with Attention Deficit Disorder with Hyperactivity described under INDICATIONS AND USAGE.
Clinical experience suggests that in psychotic children, administration of amphetamines may exacerbate symptoms of behavior disturbance and thought disorder.
Amphetamines have been reported to exacerbate motor and phonic tics and Tourette’s syndrome. Therefore clinical evaluation for tics and Tourette’s syndrome in children and their families should precede use of stimulant medications.
Data is inadequate to determine whether chronic administration of amphetamines may be associated with growth inhibition; therefore growth should be monitored during treatment. Drug Treatment is not indicated in all cases of Attention Deficit Disorder with Hyperactivity and should be considered only in light of the complete history and evaluation of the child. The decision to prescribe amphetamines should depend on the physician’s assessment of the chronicity and severity of the child’s symptoms and their appropriateness for his/her age. Prescription should not depend solely on the presence of one or more of the behavioral characteristics.
When these symptoms are associated with acute stress reactions, treatment with amphetamines is usually not indicated.
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