Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ETHRANE vs PHENDIMETRAZINE TARTRATE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Enflurane is a volatile inhalational anesthetic that potentiates GABA-A receptor activity and inhibits excitatory neurotransmission, resulting in general anesthesia.
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.
Induction and maintenance of general 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
1-5% inspired concentration via inhalation, titrated to effect for maintenance of general anesthesia.
Oral: 35 mg twice daily or three times daily, 1 hour before meals; extended-release: 105 mg once daily in the morning.
Context-sensitive half-life: approximately 2-5 minutes after short procedures; prolonged after prolonged administration due to slow washout from fat stores.
Terminal half-life 3-4 hours; clinical context: requires multiple daily dosing
Primarily hepatic via cytochrome P450 (CYP2E1); minor metabolism to fluoride ions.
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 exhaled unchanged via lungs (>95%); less than 5% metabolized in liver to fluoride ion and other metabolites, with renal excretion of metabolites.
Primarily renal (≥70% unchanged) with minor biliary/fecal elimination (<10%)
Approximately 30-40%, primarily to albumin.
10-15% bound to albumin
Vd: 1.2-2.0 L/kg, indicating extensive distribution into tissues, especially fat.
2-3 L/kg; indicates extensive tissue distribution
By inhalation: 100% as delivered; not administered orally.
Oral: approximately 80-90%
No dose adjustment required for GFR >10 m L/min; use with caution in severe renal impairment (GFR <10 m L/min) due to potential accumulation of inorganic fluoride metabolites.
Contraindicated in severe renal impairment (GFR < 30 m L/min). No specific dose adjustments for mild-moderate impairment; use with caution.
No specific Child-Pugh based adjustment; use with caution in severe hepatic impairment as metabolism may be decreased.
Not recommended in Child-Pugh class B or C. Use with caution in mild impairment.
Induction: 2-5% inspired concentration; Maintenance: 1-3% inspired concentration, adjusted to age and response.
Not recommended for children under 12 years; safety and efficacy not established.
Lower inspired concentrations (0.5-2%) recommended due to increased sensitivity and reduced clearance; titrate to effect.
Start at lower end of dosing range; monitor for increased sensitivity and cardiovascular effects.
None
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.
May cause dose-dependent cardiovascular depression,Risk of malignant hyperthermia,Potential for nephrotoxicity due to fluoride release,Hepatotoxicity risk, especially with repeated use,Neurologic effects including seizure activity at high doses
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.
Known hypersensitivity to enflurane or other halogenated anesthetics,Known or suspected susceptibility to malignant hyperthermia,Severe hepatic impairment,Uncontrolled epilepsy
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
No specific food interactions. Patient must follow preoperative fasting guidelines (nil per os, NPO) as directed by anesthesiologist to reduce risk of aspiration.
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.
FDA Category B. No evidence of teratogenicity in animal studies; human data limited. Use only if clearly needed during pregnancy, especially first trimester due to potential fetal hypoxia from maternal hypotension.
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.
Excreted in breast milk in low amounts; M/P ratio not established. Consider benefits of breastfeeding vs. risk of infant exposure. Minimal systemic absorption in infant expected.
Excreted in breast milk; M/P ratio unknown. Contraindicated in breastfeeding due to potential CNS stimulation and cardiovascular effects in infant.
No specific dose adjustments required for pregnancy; however, MAC decreases by approximately 30% during pregnancy due to hormonal changes and increased progesterone. Monitor depth of anesthesia closely.
Contraindicated in pregnancy; no dose adjustments recommended. Avoid use due to risks of hypertension and potential teratogenicity.
ETHRANE (enflurane) is a potent inhalation anesthetic. Its use is limited due to risk of seizures at high doses and potential for nephrotoxicity from fluoride ion release. Avoid in patients with history of seizures or renal impairment. Rapid induction and recovery; use with caution in hypotensive patients due to myocardial depression. Malignant hyperthermia trigger.
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.
You will receive this anesthesia medication only in a hospital setting under expert supervision.,Possible side effects include nausea, vomiting, shivering, and confusion after waking up.,Tell your doctor if you have a history of seizures, kidney problems, or muscle disorders.,Avoid driving or operating machinery for at least 24 hours after anesthesia.,Do not eat or drink for the time specified by your healthcare team before surgery.
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.
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ETHRANE vs PHENDIMETRAZINE TARTRATE, answered by our medical review team.
ETHRANE is a General Anesthetic that works by Enflurane is a volatile inhalational anesthetic that potentiates GABA-A receptor activity and inhibits excitatory neurotransmission, resulting in general anesthesia.. 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.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ETHRANE and PHENDIMETRAZINE TARTRATE 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 ETHRANE is: 1-5% inspired concentration via inhalation, titrated to effect for maintenance of general anesthesia.. 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.. 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 ETHRANE and PHENDIMETRAZINE TARTRATE 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. ETHRANE is classified as Category C. FDA Category B. No evidence of teratogenicity in animal studies; human data limited. Use only if clearly needed during pregnancy, especially first trimester due to potential fetal . 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. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.