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 the 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. Coadministration of Mixed Salts of a Single Entity Amphetamine Product and gastrointestinal alkalizing agents, such as antacids, should be avoided. 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 actions 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 dextroamphetamine saccharate, amphetamine aspartate, dextroamphetamine sulfate, amphetamine sulfate and CYP2D6 inhibitors may increase the exposure of dextroamphetamine saccharate, amphetamine aspartate, dextroamphetamine sulfate, 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 dextroamphetamine saccharate, amphetamine aspartate, dextroamphetamine sulfate, amphetamine sulfate initiation and after a dosage increase. If serotonin syndrome occurs, discontinue dextroamphetamine saccharate, amphetamine aspartate, dextroamphetamine sulfate, amphetamine sulfate and the CYP2D6 inhibitor (see WARNINGS, OVERDOSAGE). Examples of CYP2D6 Inhibitors include paroxetine and fluoxetine (also serotonergic drugs), quinidine, ritonavir.
Serotonergic Drugs
The concomitant use of dextroamphetamine saccharate, amphetamine aspartate, dextroamphetamine sulfate, 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 dextroamphetamine saccharate, amphetamine aspartate, dextroamphetamine sulfate, amphetamine sulfate initiation or dosage increase. If serotonin syndrome occurs, discontinue dextroamphetamine saccharate, amphetamine aspartate, dextroamphetamine sulfate, amphetamine sulfate and the concomitant serotonergic drug(s) (see WARNINGS and PRECAUTIONS). Examples of serotonergic drugs include selective serotonin reuptake inhibitors (SSRI), serotonin norepinephrine reuptake inhibitor (SNRI), triptans, tricyclic antidepressants, fentanyl, lithium, tramadol, tryptophan, buspirone, St. John’s Wort.
MAO Inhibitors
MAOI antidepressants, as well as a metabolite of furazolidone, slow amphetamine metabolism. This slowing potentiates amphetamines, increasing their effect 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 receptors, thus inhibiting the central stimulant effects of amphetamines, and can be used to treat amphetamine poisoning.
Ethosuximide
Amphetamines may delay intestinal absorption of ethosuximide.
Haloperidol
Haloperidol blocks dopamine receptors, thus inhibiting the central stimulant effects of amphetamines.
Lithium Carbonate
The anorectic 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; coadministration of phenobarbital may produce a synergistic anticonvulsant action.
Phenytoin
Amphetamines may delay intestinal absorption of phenytoin; coadministration of phenytoin may produce a synergistic anticonvulsant action.
Propoxyphene
In cases of propoxyphene overdosage, amphetamine CNS stimulation is potentiated and fatal convulsions can occur.
Proton Pump Inhibitors
PPIs act on proton pumps by blocking acid production, thereby reducing gastric acidity. When Mixed Salts of a Single Entity Amphetamine Product (20 mg single-dose) was administered concomitantly with the proton pump inhibitor, omeprazole (40 mg once daily for 14 days), the median Tmax of d-amphetamine was decreased by 1.25 hours (from 4 to 2.75 hours), and the median Tmax of l-amphetamine was decreased by 2.5 hours (from 5.5 to 3 hours), compared to Mixed Salts of a Single Entity Amphetamine Product administered alone. The AUC and Cmax of each moiety were unaffected. Therefore, coadministration of Mixed Salts of a Single Entity Amphetamine Product and proton pump inhibitors should be monitored for changes in clinical effect.
Veratrum Alkaloids
Amphetamines inhibit the hypotensive effect of veratrum alkaloids.