Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
FASTIN vs ETOMIDATE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Sympathomimetic amine that promotes release of norepinephrine and dopamine from presynaptic nerve terminals in the hypothalamus, suppressing appetite.
Etomidate is a nonbarbiturate hypnotic agent that acts as a positive allosteric modulator of the gamma-aminobutyric acid (GABA) type A receptor, enhancing GABA-mediated inhibition in the central nervous system. It produces rapid anesthesia with minimal cardiovascular and respiratory depression.
Short-term adjunct in exogenous obesity,Off-label: Attention deficit hyperactivity disorder (ADHD)
Induction of general anesthesia,Procedural sedation (off-label),Rapid sequence intubation (off-label)
30 mg orally once daily in the morning, administered as a single dose.
Induction: 0.2–0.6 mg/kg IV over 30–60 seconds. Maintenance: 10–20 mcg/kg/min IV continuous infusion.
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.
Terminal elimination half-life: 2.9–5.3 hours (context: redistribution shortens clinical effect; hepatic impairment prolongs).
Hepatic metabolism via CYP3A4 and CYP2D6; active metabolite phendimetrazine (for some formulations).
Etomidate is extensively metabolized in the liver via hydrolysis of the ester side chain by hepatic esterases to its principal metabolite, etomidate carboxylic acid. A minor metabolite is formed via N-demethylation. Metabolites are inactive.
Primarily renal (approximately 70-80% unchanged) and biliary/fecal (20-30% as metabolites). Urinary excretion is p H-dependent; acidic urine increases elimination.
Renal: 75% as metabolite (carboxylic acid), 2% unchanged; fecal/biliary: minimal.
Approximately 40-50% bound to plasma proteins (albumin).
76% bound to albumin.
Approximately 3-5 L/kg. High Vd indicates extensive tissue distribution, including brain.
Vd: 2.5–4.5 L/kg (large, indicating extensive tissue uptake).
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.
IV: 100% (only route used clinically).
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 dose adjustment required for renal impairment. Hemodialysis does not alter dosing. Use caution in severe renal failure due to propylene glycol vehicle if prolonged infusion.
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.
No specific adjustment for Child-Pugh class. However, prolonged effect may occur in severe hepatic impairment; reduce induction dose by 50% and titrate to effect.
Not recommended for pediatric patients under 16 years of age due to lack of safety and efficacy data.
Induction: 0.2–0.6 mg/kg IV (max 40 mg). Age >10 years: use adult dosing. Neonates and infants: reduce dose to 0.3 mg/kg due to higher volume of distribution.
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.
Induction: 0.15–0.3 mg/kg IV (50% reduction of adult dose) due to decreased clearance and increased sensitivity. Use lower end of dosing range.
None.
Etomidate has been associated with mortality in children. It should not be used in children younger than 6 months of age. (This warning is included in the prescribing information based on FDA labeling; specific text may vary.)
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).
Inhibition of adrenal steroidogenesis (adrenal suppression) due to blockade of 11-beta-hydroxylase, leading to decreased cortisol and aldosterone production; may persist for 12-24 hours after single dose,Myoclonic movements during induction (involuntary muscle contractions),Hypotension and bradycardia (less common than with other induction agents),Venous irritation and pain on injection (may be reduced by using larger veins)
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.
Hypersensitivity to etomidate,Patients with acute porphyria (may be porphyrinogenic)
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.
No specific food interactions are known. Etomidate is administered intravenously and does not have oral bioavailability. However, concurrent use of drugs that affect CYP3A4 (e.g., grapefruit juice) is not clinically significant due to IV route.
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.
Etomidate is classified as FDA Pregnancy Category C. Animal studies have shown embryotoxicity and teratogenicity at doses higher than human doses. There are no adequate and well-controlled studies in pregnant women. First trimester exposure may be associated with a slightly increased risk of congenital malformations, but data are limited. Risks to the fetus should be weighed against the benefits of maternal anesthesia. The drug is not recommended during pregnancy unless clearly needed, especially during organogenesis. In the second and third trimesters, etomidate may cause fetal central nervous system depression and respiratory depression if used near term.
Excreted in human milk; M/P ratio not established. Potential for adverse effects in nursing infants (irritability, poor feeding). Contraindicated during breastfeeding.
It is unknown whether etomidate is excreted in human breast milk. The molecular weight (244.3) suggests potential excretion into milk. The milk-to-plasma ratio (M/P) has not been determined. Due to the short half-life (2–5 hours) and use as a single induction dose, transfer to the infant is likely minimal. However, caution is advised. The American Academy of Pediatrics classifies etomidate as 'compatible' with breastfeeding after a single dose, but data are insufficient for repeated or prolonged use. Infants should be monitored for sedation and respiratory depression.
Contraindicated in pregnancy; no dose adjustments recommended.
No specific dose adjustments are recommended for etomidate during pregnancy, but the dose should be individualized to achieve the desired level of anesthesia with the lowest effective dose. Physiologic changes in pregnancy (e.g., increased plasma volume, altered protein binding) may affect pharmacokinetics, but etomidate is rapidly redistributed and has a short duration of action. The standard induction dose of 0.2–0.6 mg/kg IV is used. Close monitoring of maternal and fetal status is advised. In cesarean section, lower doses may be considered to reduce fetal depression.
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.
Etomidate is an induction agent of choice in hemodynamically unstable patients due to minimal cardiovascular depression. Adrenal suppression occurs even after a single dose, manifesting as decreased cortisol and aldosterone synthesis via 11β-hydroxylase inhibition. Administer slowly over 30-60 seconds to reduce myoclonus and pain on injection. Use a lower dose (0.2-0.3 mg/kg IV) in elderly or debilitated patients. Etomidate is not recommended for rapid sequence intubation in septic shock due to risk of adrenal insufficiency; consider ketamine as alternative. Prolonged infusion is not advised due to propylene glycol vehicle and adrenal suppression.
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.
You may experience brief involuntary muscle movements during injection, which are usually harmless.,Tell your doctor if you have adrenal gland problems or are taking corticosteroids.,This drug may cause a temporary decrease in your body's ability to produce stress hormones.,Avoid driving or operating machinery until the effects of the medication have completely worn off.,Report any severe pain at the injection site or unusual weakness after the procedure.
No interactions on record
"Concurrent administration of etomidate and fluoxetine may potentiate the anesthetic and sedative effects, as fluoxetine inhibits CYP3A4 which is involved in the metabolism of etomidate, leading to increased etomidate plasma concentrations and prolonged recovery time. Additionally, both drugs can cause QTc interval prolongation, increasing the risk of torsades de pointes and other ventricular arrhythmias. Patients may experience enhanced central nervous system depression, respiratory depression, and hypotension."
"The combination of Promazine, a phenothiazine antipsychotic with strong alpha-adrenergic blocking activity, and Etomidate, a non-barbiturate hypnotic used for induction of anesthesia, can lead to an increased risk of hypotension due to additive vasodilatory effects. Promazine's alpha-1 receptor antagonism impairs compensatory vasoconstriction, while Etomidate suppresses adrenal cortisol synthesis, potentially blunting the stress response and further reducing hemodynamic stability. Clinically, this interaction may result in profound hypotension, especially in hypovolemic or elderly patients, requiring careful dose titration and monitoring."
"The coadministration of oxazepam, a benzodiazepine that enhances GABA-A receptor activity, with etomidate, a non-barbiturate anesthetic that also potentiates GABA-A receptor function, results in additive central nervous system (CNS) depression. This synergistic interaction can lead to excessive sedation, respiratory depression, hypotension, and prolonged recovery from anesthesia. Patients are at increased risk of apnea, hypoxia, and hemodynamic instability, particularly during induction and maintenance of anesthesia."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about FASTIN vs ETOMIDATE, answered by our medical review team.
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.. ETOMIDATE is a General Anesthetic that works by Etomidate is a nonbarbiturate hypnotic agent that acts as a positive allosteric modulator of the gamma-aminobutyric acid (GABA) type A receptor, enhancing GABA-mediated inhibition in the central nervous system. It produces rapid anesthesia with minimal cardiovascular and respiratory depression.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between FASTIN and ETOMIDATE 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 FASTIN is: 30 mg orally once daily in the morning, administered as a single dose.. The standard adult dose of ETOMIDATE is: Induction: 0.2–0.6 mg/kg IV over 30–60 seconds. Maintenance: 10–20 mcg/kg/min IV continuous infusion.. 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 FASTIN and ETOMIDATE 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. 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. ETOMIDATE is classified as Category C. Etomidate is classified as FDA Pregnancy Category C. Animal studies have shown embryotoxicity and teratogenicity at doses higher than human doses. There are no adequate and well-co. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.