FLUOTHANE
Clinical safety rating
cautionComprehensive clinical and safety monograph for FLUOTHANE (FLUOTHANE).
Halothane enhances GABA-A receptor activity and inhibits NMDA receptors, leading to neuronal hyperpolarization and decreased excitability. It also potentiates glycine receptor function and disrupts synaptic transmission via interaction with voltage-gated sodium channels.
| Metabolism | Hepatic metabolism via cytochrome P450 enzymes (CYP2E1 major, CYP2A6 minor) to trifluoroacetic acid, chloride, and bromide ions; reductive metabolism under hypoxic conditions produces potentially hepatotoxic intermediates. |
| Excretion | Primarily exhaled unchanged via the lungs; negligible renal (0.5% as metabolites) and fecal elimination. |
| Half-life | Terminal elimination half-life is biphasic: initial 2-5 minutes (rapid redistribution), terminal 15-20 hours for trace amounts in adipose tissue due to slow release; contextually, emergence from anesthesia occurs within minutes. |
| Protein binding | ~40-50% bound to albumin. |
| Volume of Distribution | 2-5 L/kg; indicates extensive tissue distribution, particularly in adipose and brain. |
| Bioavailability | Inhalation: 100% (administered as gas); no other relevant routes. |
| Onset of Action | Inhalation: within 30-60 seconds (induction); dose-dependent. |
| Duration of Action | Inhalation: 5-10 minutes after discontinuation for emergence; prolonged with higher cumulative doses. |
| Molecular Weight | 197.38 |
Induction: 0.5-3% halothane in oxygen or nitrous oxide/oxygen; maintenance: 0.5-1.5%.
| Dosage form | LIQUID |
| Renal impairment | No dose adjustment required for renal impairment; halothane is minimally excreted renally. |
| Liver impairment | Contraindicated in patients with Child-Pugh class B or C cirrhosis due to risk of hepatotoxicity; use with caution in mild impairment with reduced doses. |
| Pediatric use | Induction: 0.5-2% halothane in oxygen; maintenance: 0.3-1%. Dose based on response. |
| Geriatric use | Reduce induction concentration to 0.5-1% and maintenance to 0.5% due to increased sensitivity and slower clearance. |
| 1st trimester | Halothane is not recommended during first trimester unless absolutely necessary; animal studies show fetal harm and human data are limited. |
| 2nd trimester | May be used if clinically indicated, but caution due to potential uterine relaxation and fetal effects. |
| 3rd trimester | Use with caution; halothane relaxes uterine muscle, may increase risk of hemorrhage, and can cause neonatal depression. |
Clinical note
Comprehensive clinical and safety monograph for FLUOTHANE (FLUOTHANE).
| Placental transfer | Rapidly crosses the placenta; fetal concentrations reach 50-80% of maternal levels within minutes. |
| Breastfeeding | Halothane is excreted into breast milk in small amounts; due to short half-life and minimal oral bioavailability, risk to infant is low. However, avoid breastfeeding until maternal clearance is complete (several hours post-anesthesia). |
| Lactation Rating | L2 (Safer) |
| Teratogenic Risk | FDA Pregnancy Category C. First trimester: Increased risk of congenital anomalies (cleft palate, skeletal defects) in animal studies; avoid unless essential. Second and third trimesters: Prolonged exposure may cause neonatal respiratory depression, hypotonia, and thermoregulatory instability; risk of fetal hypoxia due to maternal hypotension. |
| Fetal Monitoring | Continuous fetal heart rate monitoring during maternal anesthesia. Monitor maternal blood pressure and uterine tone to prevent placental hypoperfusion. Assess neonatal Apgar scores and respiratory function post-delivery. |
| Fertility Effects | No specific data; halothane does not adversely affect human fertility. Occupational exposure may be associated with menstrual disorders and spontaneous abortion in healthcare workers (reversible with adequate scavenging). |
■ FDA Black Box Warning
Halothane is associated with a risk of life-threatening hepatic injury, including fatal hepatic necrosis, primarily following repeated exposure or in patients with known hypersensitivity. It should be avoided in patients with a history of unexplained jaundice or fever after halothane administration.
| Serious Effects |
Known or suspected malignant hyperthermia susceptibilityHistory of halothane-induced hepatitis or unexplained jaundice after previous halothane exposureSignificant hepatic dysfunction
| Precautions | Risk of hepatic necrosis (especially with repeated use); malignant hyperthermia; respiratory depression; hypotension; cardiac arrhythmias (including sensitization to catecholamines); increased intracranial pressure; requires trained personnel and monitoring; use caution in patients with hepatic disease. |
| Food/Dietary | No specific food interactions known, but fasting is required preoperatively to prevent aspiration pneumonitis caused by relaxation of the lower esophageal sphincter and loss of airway reflexes. |
| Clinical Pearls | Halothane is a potent inhalational anesthetic with low blood-gas solubility, allowing rapid induction and emergence. It sensitizes the myocardium to catecholamines, increasing risk of arrhythmias, especially with epinephrine use. Halothane can cause hepatic necrosis, particularly with repeated exposure (halothane hepatitis). Avoid in patients with unexplained jaundice after prior halothane use. Use low concentrations with spontaneous ventilation to prevent respiratory depression. |
| Patient Advice | Avoid food or drink for at least 6-8 hours before surgery to reduce aspiration risk. · Report any history of liver disease or allergic reactions to anesthesia. · You may experience shivering or nausea after waking up from anesthesia. · Do not drive or operate machinery for at least 24 hours after anesthesia. · Inform your doctor if you notice yellowing of skin or eyes, dark urine, or severe fatigue after surgery. |
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