Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ETHRANE vs FASTIN
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.
Sympathomimetic amine that promotes release of norepinephrine and dopamine from presynaptic nerve terminals in the hypothalamus, suppressing appetite.
Induction and maintenance of general anesthesia
Short-term adjunct in exogenous obesity,Off-label: Attention deficit hyperactivity disorder (ADHD)
1-5% inspired concentration via inhalation, titrated to effect for maintenance of general anesthesia.
30 mg orally once daily in the morning, administered as a single dose.
Context-sensitive half-life: approximately 2-5 minutes after short procedures; prolonged after prolonged administration due to slow washout from fat stores.
Terminal elimination half-life is approximately 16-20 hours for the immediate-release formulation. With sustained-release forms, effective half-life may extend to 24-34 hours due to prolonged absorption. Clinical context: time to reach steady state is about 3-5 days.
Primarily hepatic via cytochrome P450 (CYP2E1); minor metabolism to fluoride ions.
Hepatic metabolism via CYP3A4 and CYP2D6; active metabolite phendimetrazine (for some formulations).
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 (approximately 70-80% unchanged) and biliary/fecal (20-30% as metabolites). Urinary excretion is p H-dependent; acidic urine increases elimination.
Approximately 30-40%, primarily to albumin.
Approximately 40-50% bound to plasma proteins (albumin).
Vd: 1.2-2.0 L/kg, indicating extensive distribution into tissues, especially fat.
Approximately 3-5 L/kg. High Vd indicates extensive tissue distribution, including brain.
By inhalation: 100% as delivered; not administered orally.
Oral immediate-release: ~90% (high first-pass metabolism; absolute bioavailability is lower, but systemic exposure is adequate). Oral sustained-release: similar extent but with prolonged absorption.
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 (e GFR <30 m L/min/1.73 m²). For moderate impairment (e GFR 30-59 m L/min/1.73 m²), reduce dose to 15 mg once daily.
No specific Child-Pugh based adjustment; use with caution in severe hepatic impairment as metabolism may be decreased.
Contraindicated in Child-Pugh class C cirrhosis. In Child-Pugh class A or B, initiate at 15 mg once daily and titrate cautiously to maximum 30 mg once daily.
Induction: 2-5% inspired concentration; Maintenance: 1-3% inspired concentration, adjusted to age and response.
Not recommended for pediatric patients under 16 years of age due to lack of safety and efficacy data.
Lower inspired concentrations (0.5-2%) recommended due to increased sensitivity and reduced clearance; titrate to effect.
Initiating at 15 mg once daily is recommended due to increased sensitivity and potential for central nervous system adverse effects; maximum dose 30 mg once daily.
None
None.
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
Cardiovascular events (hypertension, tachycardia, stroke), psychiatric adverse effects (psychosis, dependence), primary pulmonary hypertension, valvular heart disease, tolerance, withdrawal symptoms, glaucoma, hyperthyroidism, seizure disorder, diabetes (dose adjustment required), elderly patients (higher sensitivity).
Known hypersensitivity to enflurane or other halogenated anesthetics,Known or suspected susceptibility to malignant hyperthermia,Severe hepatic impairment,Uncontrolled epilepsy
Cardiovascular disease (e.g., coronary artery disease, arrhythmias, hypertension), hyperthyroidism, glaucoma, agitated states, history of drug abuse, MAOIs (concurrent or within 14 days), hypersensitivity to sympathomimetics.
No specific food interactions. Patient must follow preoperative fasting guidelines (nil per os, NPO) as directed by anesthesiologist to reduce risk of aspiration.
Avoid excessive caffeine intake (e.g., coffee, tea, cola, energy drinks) as it may potentiate CNS and cardiovascular effects. Grapefruit juice may alter drug metabolism; avoid concurrent consumption. Maintain a balanced, reduced-calorie diet as part of the weight loss plan. Alcohol should be avoided due to potential additive CNS effects.
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.
FDA Pregnancy Category X. First trimester: Increased risk of oral clefts and cardiac malformations with amphetamine use. Second and third trimesters: Risk of premature delivery, low birth weight, and neonatal withdrawal syndrome. Avoid use in pregnancy.
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 human milk; M/P ratio not established. Potential for adverse effects in nursing infants (irritability, poor feeding). Contraindicated during breastfeeding.
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.
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.
Fastin (phentermine) is a sympathomimetic amine indicated for short-term (up to 12 weeks) monotherapy for obesity. It should be used in conjunction with a reduced-calorie diet and exercise. Avoid co-administration with MAOIs or within 14 days of MAOI use due to hypertensive crisis risk. Use with caution in patients with hypertension, diabetes, or history of drug abuse. Monitor blood pressure and heart rate regularly. Tachyphylaxis may develop; discontinue if tolerance occurs. Do not use in patients with advanced arteriosclerosis, hyperthyroidism, glaucoma, or agitated states.
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 Fastin exactly as prescribed, usually once daily in the morning to avoid insomnia.,Do not crush or chew the extended-release capsule; swallow whole.,Avoid taking late in the day to prevent difficulty sleeping.,Report any chest pain, palpitations, shortness of breath, or dizziness immediately.,Do not increase dose or take more frequently than prescribed; risk of dependence and side effects.,Fastin is for short-term use only (up to 12 weeks) and should be combined with a reduced-calorie diet and exercise.,Do not use if you have taken an MAO inhibitor in the last 14 days.,Avoid alcohol and other CNS stimulants (e.g., caffeine in large amounts) as they may increase side effects.,Do not stop abruptly; follow your doctor's instructions for tapering off.,Keep out of reach of children; misuse can cause severe cardiac toxicity.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ETHRANE vs FASTIN, 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.. FASTIN is a Sympathomimetic Anorectic that works by Sympathomimetic amine that promotes release of norepinephrine and dopamine from presynaptic nerve terminals in the hypothalamus, suppressing appetite.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ETHRANE and FASTIN 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 FASTIN is: 30 mg orally once daily in the morning, administered as a single dose.. 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 FASTIN 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 . FASTIN is classified as Category C. FDA Pregnancy Category X. First trimester: Increased risk of oral clefts and cardiac malformations with amphetamine use. Second and third trimesters: Risk of premature delivery, lo. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.