Benzphetamine

Pronunciation

(benz FET a meen)

U.S. Brand Names

Didrex®

Synonyms

Benzphetamine Hydrochloride

Generic Available

Canadian Brand Names

Didrex®

Use

Short-term adjunct in exogenous obesity

Restrictions

C-III

Pregnancy Risk Factor

Contraindications

Hypersensitivity or idiosyncrasy to sympathomimetic amines. Patients with advanced arteriosclerosis, symptomatic cardiovascular disease, moderate to severe hypertension (stage II or III), hyperthyroidism, glaucoma, agitated states, patients with a history of drug abuse, pregnancy, and during or within 14 days following MAO inhibitor therapy. Concurrent use with other anorectic agents; stimulant medications are contraindicated for use in children with attention-deficit/hyperactivity disorders and concomitant Tourette's syndrome or tics. Not recommended for children <12 years of age.

Warnings/Precautions

Cardiovascular disease, nephritis, angina pectoris, hypertension, glaucoma, patients with a history of drug abuse; stimulants may unmask tics in individuals with coexisting Tourette's syndrome.

Serious, potentially life-threatening toxicities may occur when thyroid hormones (at dosages above usual daily hormonal requirements) are used in combination with sympathomimetic amines to induce weight loss. Treatment of obesity is not an approved use for thyroid hormone.

Adverse Reactions

Frequency not defined.

Cardiovascular: Hypertension, palpitation, tachycardia, chest pain, T-wave changes, arrhythmia, pulmonary hypertension, valvulopathy

Central nervous system: Euphoria, nervousness, insomnia, restlessness, dizziness, anxiety, headache, agitation, confusion, mental depression, psychosis, CVA, seizure

Dermatologic: Alopecia, urticaria, skin rash, ecchymosis, erythema

Endocrine & metabolic: Changes in libido, gynecomastia, menstrual irregularities, porphyria

Gastrointestinal: Nausea, vomiting, abdominal cramps, constipation, xerostomia, metallic taste

Genitourinary: Impotence

Hematologic: Bone marrow depression, agranulocytosis, leukopenia

Neuromuscular & skeletal: Tremor

Ocular: Blurred vision, mydriasis

Drug Interactions

Substrate of CYP2B6 (minor), 3A4 (major)

Acidifiers: Very large doses of potassium acid phosphate or ammonium chloride may increase the renal elimination of amphetamines due to urinary acidification

Alkalinizers: Large doses of sodium bicarbonate or other alkalinizers may increase renal tubular reabsorption (decreased elimination) and diminish the effect of amphetamine; includes potassium or sodium citrate and acetate

Antipsychotics: Efficacy of amphetamines may be decreased by antipsychotics; in addition, amphetamines may induce an increase in psychotic symptoms in some patients

CYP3A4 inducers: CYP3A4 inducers may decrease the levels/effects of benzphetamine. Example inducers include aminoglutethimide, carbamazepine, nafcillin, nevirapine, phenobarbital, phenytoin, and rifamycins.

CYP3A4 inhibitors: May increase the levels/effects of benzphetamine. Example inhibitors include azole antifungals, ciprofloxacin, clarithromycin, diclofenac, doxycycline, erythromycin, imatinib, isoniazid, nefazodone, nicardipine, propofol, protease inhibitors, quinidine, and verapamil.

Furazolidone: Amphetamines may induce hypertensive episodes in patients receiving furazolidone

Guanethidine: Amphetamines inhibit the antihypertensive response to guanethidine; probably also may occur with guanadrel

MAO inhibitors: Severe hypertensive episodes have occurred with amphetamine when used in patients receiving MAO inhibitors; concurrent use or use within 14 days is contraindicated

Norepinephrine: Amphetamines may enhance the pressor response to norepinephrine

Sibutramine: Concurrent use of sibutramine and amphetamines may cause severe hypertension and tachycardia; use is contraindicated in product

SSRIs: Amphetamines may increase the potential for serotonin syndrome when used concurrently with selective serotonin reuptake inhibitors (including fluoxetine, fluvoxamine, paroxetine, and sertraline)

Tricyclic antidepressants: Concurrent of amphetamines with TCAs may result in hypertension and CNS stimulation; avoid this combination

Mechanism of Action

Noncatechol sympathomimetic amines with pharmacologic actions similar to ephedrine; require breakdown by monoamine oxidase for inactivation; produce central nervous system and respiratory stimulation, a pressor response, mydriasis, bronchodilation, and contraction of the urinary sphincter; thought to have a direct effect on both alpha- and beta-receptor sites in the peripheral system, as well as release stores of norepinephrine in adrenergic nerve terminals; central nervous system action is thought to occur in the cerebral cortex and reticular activating system; anorexigenic effect is probably secondary to the CNS-stimulating effect; the site of action is probably the hypothalamic feeding center.

Dosage

Adults: Oral: Dose should be individualized based on patient response: Initial: 25-50 mg once daily; titrate to 25-50 mg 1-3 times/day; once-daily dosing should be administered midmorning or midafternoon; maximum dose: 50 mg 3 times/day

Patient Education

Take during the day to avoid insomnia; do not discontinue abruptly, may be addicting with prolonged use; use caution driving or engaging in tasks requiring alertness until response to medication is known

Nursing Implications

Monitor CNS

Dental Health: Effects on Dental Treatment

Key adverse event(s) related to dental treatment: Xerostomia (normal salivary flow resumes upon discontinuation) and metallic taste.

Dental Health: Vasoconstrictor/Local Anesthetic Precautions

Use with caution since amphetamines have actions similar to epinephrine and norepinephrine

Dosage Forms

Tablet, as hydrochloride: 50 mg

International Brand Names

Didrex® (CA)

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