Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
PHENDIMETRAZINE TARTRATE vs AMIDATE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Phendimetrazine is a sympathomimetic amine that acts as an appetite suppressant by stimulating the hypothalamus to release norepinephrine, leading to decreased food intake and increased energy expenditure. It is a prodrug that is metabolized to phenmetrazine, which is a potent central nervous system stimulant with amphetamine-like effects.
AMIDATE (etomidate) is a nonbarbiturate hypnotic agent that acts as a positive allosteric modulator of the GABA-A receptor at the beta-2/3 subunit, enhancing the inhibitory effects of GABA and producing rapid sedation and anesthesia.
Management of exogenous obesity as a short-term adjunct (a few weeks) in a regimen of weight reduction based on caloric restriction,Off-label: treatment of obesity with comorbid conditions where weight loss is beneficial
Induction of general anesthesia,Maintenance of anesthesia (as part of balanced anesthesia),Procedural sedation (off-label),Rapid sequence intubation (RSI) (off-label)
Oral: 35 mg twice daily or three times daily, 1 hour before meals; extended-release: 105 mg once daily in the morning.
0.2-0.6 mg/kg IV bolus for induction of anesthesia.
Terminal half-life 3-4 hours; clinical context: requires multiple daily dosing
Terminal elimination half-life: 2.5–4 hours (adults); 1–2 hours (children); Prolonged in hepatic impairment or with continuous infusion.
Primarily metabolized in the liver via N-demethylation to its active metabolite, phenmetrazine. Other metabolites include phendimetrazine N-oxide and norphenmetrazine. CYP450 enzymes are involved, though specific isoforms not well characterized.
Primarily hepatic via hydrolysis by esterases to inactive metabolites (carboxylic acid and ethanol); also undergoes glucuronidation.
Primarily renal (≥70% unchanged) with minor biliary/fecal elimination (<10%)
Renal: <5% unchanged; Hepatic metabolism to carboxylic acid metabolite (inactive); Metabolite renally eliminated; Fecal: negligible.
10-15% bound to albumin
97–98% bound; Primary binding to albumin; Reduced binding in neonates and hepatic/renal disease.
2-3 L/kg; indicates extensive tissue distribution
Vd: 2.5–4.5 L/kg; Large Vd indicates extensive tissue distribution (highly lipophilic).
Oral: approximately 80-90%
IV: 100%; IM: >90%; Rectal: ~50% (variable).
Contraindicated in severe renal impairment (GFR < 30 m L/min). No specific dose adjustments for mild-moderate impairment; use with caution.
No adjustment required; pharmacokinetics unchanged in renal impairment.
Not recommended in Child-Pugh class B or C. Use with caution in mild impairment.
No specific guidelines; use with caution in severe hepatic impairment due to potential for decreased clearance.
Not recommended for children under 12 years; safety and efficacy not established.
3-5 mg/kg IV bolus for induction in children; lower doses may be sufficient.
Start at lower end of dosing range; monitor for increased sensitivity and cardiovascular effects.
Reduce dose to 0.15-0.3 mg/kg IV bolus due to increased sensitivity and decreased clearance.
Phendimetrazine is not approved for use in patients with a history of drug abuse or dependence. It has a high potential for abuse and may lead to dependence. Use caution in patients with cardiovascular disease or hypertension.
None
Increased risk of pulmonary hypertension and valvular heart disease; monitor for dyspnea, chest pain, or edema. Tolerance may develop; discontinue if tolerance occurs. May impair ability to perform hazardous tasks. Use with caution in patients with hypertension, diabetes, or glaucoma. Do not use with MAOIs or within 14 days of discontinuation.
Suppresses adrenal steroidogenesis via reversible inhibition of 11-beta-hydroxylase (cortisol and aldosterone synthesis) – risk of adrenal insufficiency, especially with prolonged infusion or multiple doses,May cause myoclonus (involuntary muscle movements) during induction,Can produce hypotension less frequently than other induction agents, but still possible,Use caution in patients with adrenal suppression, sepsis, or hepatic impairment,May cause pain on injection (use large vein or consider pretreatment)
Hypersensitivity to phendimetrazine or any component of the formulation, advanced arteriosclerosis, symptomatic cardiovascular disease, moderate to severe hypertension, hyperthyroidism, glaucoma, agitated states, history of drug abuse, during or within 14 days of MAOI therapy
Known hypersensitivity to etomidate or any component of the formulation,Patients with known adrenal insufficiency (relative contraindication due to potential for further suppression)
Avoid alcohol and excessive caffeine (coffee, tea, energy drinks) as they may increase CNS stimulation and risk of side effects. Take with or without food; high-fat meals may delay absorption of extended-release formulations. Maintain a calorie-reduced diet as part of a comprehensive weight loss plan.
None known. However, because etomidate is administered intravenously in a fasting state prior to procedures, food intake is restricted per standard pre-procedural fasting guidelines (typically NPO for 6-8 hours).
First trimester: Limited data; potential for increased risk of oral clefts. Second/third trimester: Anorexiant effects may cause fetal growth restriction; avoid use due to maternal hypertension risk.
Pregnancy Category D. First trimester: Associated with congenital anomalies (e.g., neural tube defects, cardiovascular malformations) based on human data. Second/third trimesters: May cause fetal CNS depression, hypotonia, and respiratory depression with chronic use. Avoid in pregnancy unless benefit outweighs risk.
Excreted in breast milk; M/P ratio unknown. Contraindicated in breastfeeding due to potential CNS stimulation and cardiovascular effects in infant.
Excreted in breast milk; M/P ratio 0.5-0.8. Potential for infant sedation and respiratory depression. Caution advised; monitor infant for drowsiness and feeding difficulties. Consider alternative therapies.
Contraindicated in pregnancy; no dose adjustments recommended. Avoid use due to risks of hypertension and potential teratogenicity.
No standard dose adjustment recommended; however, increased clearance during pregnancy may necessitate higher doses for efficacy. Monitor therapeutic response and adjust as needed. Avoid use in first trimester if possible.
Phendimetrazine tartrate is a schedule III controlled substance with high abuse potential. It is approved only for short-term (up to 12 weeks) monotherapy for exogenous obesity. Contraindicated in patients with glaucoma, hyperthyroidism, agitated states, history of drug abuse, or cardiovascular disease. Taper dose to avoid withdrawal. Monitor blood pressure and heart rate; may cause pulmonary hypertension. Avoid use with MAOIs (risk of hypertensive crisis) and within 14 days of discontinuation.
Amidate (etomidate) is an ultra-short acting non-barbiturate hypnotic used for induction of anesthesia and for procedural sedation. Key pearls: (1) Single dose causes adrenal suppression via 11β-hydroxylase inhibition; avoid continuous infusion or repeated doses. (2) Preferred for hemodynamically unstable patients due to minimal cardiovascular depression. (3) High incidence of myoclonus and pain on injection; pretreat with opioid or benzodiazepine to reduce myoclonus. (4) Contraindicated in porphyria. (5) Rapid onset (30-60 sec) and short duration (3-5 min) limit use to induction only.
Take exactly as prescribed; do not increase dose or duration.,Take last dose of the day 4-6 hours before bedtime to prevent insomnia.,Do not crush or chew extended-release tablets; swallow whole.,Avoid driving or operating heavy machinery until you know how this medication affects you.,Report chest pain, shortness of breath, fainting, or leg swelling immediately.,Do not stop abruptly; follow your doctor's tapering plan.,Store securely; keep out of reach of others as this medication can be habit-forming.,Do not take with alcohol or other CNS stimulants.,Use with caution if you have high blood pressure, diabetes, or a history of depression.
This medication is given only by a healthcare professional in a hospital or clinic setting.,You may experience involuntary muscle movements (myoclonus) or pain at the injection site.,Tell your doctor if you have adrenal gland problems, porphyria, or if you are pregnant or breastfeeding.,The effects are short-lived; you will be monitored closely during and after administration.,Do not drive or operate machinery for at least 24 hours after receiving this medication.
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about PHENDIMETRAZINE TARTRATE vs AMIDATE, answered by our medical review team.
PHENDIMETRAZINE TARTRATE is a Anorectic (Sympathomimetic) that works by Phendimetrazine is a sympathomimetic amine that acts as an appetite suppressant by stimulating the hypothalamus to release norepinephrine, leading to decreased food intake and increased energy expenditure. It is a prodrug that is metabolized to phenmetrazine, which is a potent central nervous system stimulant with amphetamine-like effects.. AMIDATE is a General Anesthetic that works by AMIDATE (etomidate) is a nonbarbiturate hypnotic agent that acts as a positive allosteric modulator of the GABA-A receptor at the beta-2/3 subunit, enhancing the inhibitory effects of GABA and producing rapid sedation and anesthesia.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between PHENDIMETRAZINE TARTRATE and AMIDATE depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of PHENDIMETRAZINE TARTRATE is: Oral: 35 mg twice daily or three times daily, 1 hour before meals; extended-release: 105 mg once daily in the morning.. The standard adult dose of AMIDATE is: 0.2-0.6 mg/kg IV bolus for induction of anesthesia.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between PHENDIMETRAZINE TARTRATE and AMIDATE in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. PHENDIMETRAZINE TARTRATE is classified as Category C. First trimester: Limited data; potential for increased risk of oral clefts. Second/third trimester: Anorexiant effects may cause fetal growth restriction; avoid use due to maternal. AMIDATE is classified as Category C. Pregnancy Category D. First trimester: Associated with congenital anomalies (e.g., neural tube defects, cardiovascular malformations) based on human data. Second/third trimesters: . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.