Halothane is a volatile, non-flammable, halogenated hydrocarbon general inhalation anesthetic. It is a potent agent providing rapid induction and recovery, with good muscle relaxation and bronchodilation. Its use has declined significantly in developed nations due to the risk of severe hepatotoxicity (halothane hepatitis), but it remains in use in certain cost-sensitive and resource-limited settings in India, primarily for pediatric induction and in veterinary practice. It is typically administered via a calibrated vaporizer in a mixture of oxygen or nitrous oxide-oxygen.
Adult: Induction: 2-4% vapor concentration in oxygen/nitrous oxide-oxygen. Maintenance: 0.5-2.0% vapor concentration. Dose is titrated to clinical effect (BP, HR, depth of anesthesia).
Note: Administered ONLY via a calibrated, temperature-compensated, specifically designed halothane vaporizer. Must be used with adequate oxygen flow (minimum 30%). Never use with epinephrine-containing local anesthetics in doses >100 mcg/10 minutes due to risk of ventricular arrhythmias. Protect from light. Do not use if discolored (additives include thymol as stabilizer; yellowing indicates decomposition).
Halothane's precise mechanism is multifactorial. It potentiates inhibitory neurotransmission (GABA-A, glycine receptors) and inhibits excitatory neurotransmission (NMDA glutamate receptors). It activates potassium channels (TREK-1) and inhibits neuronal sodium channels. The overall effect is a dose-dependent, reversible depression of the central nervous system, leading to loss of consciousness, amnesia, analgesia, and muscle relaxation.
Pregnancy: Category C (US FDA). Animal studies show teratogenic effects. Avoid in first trimester unless absolutely necessary. Can cause uterine relaxation and increase blood loss during cesarean section. Crosses placenta; can cause neonatal depression.
Driving: Patients must be advised NOT to drive, operate machinery, or make important decisions for at least 24 hours after general anesthesia with halothane due to residual CNS effects and possible hangover.
| Aminophylline, Theophylline | Increased risk of cardiac arrhythmias | Major |
| Epinephrine, Norepinephrine | Markedly increased risk of severe ventricular arrhythmias; dose must be limited | Major |
| Non-Depolarizing Muscle Relaxants (e.g., Atracurium, Vecuronium) | Potentiation of neuromuscular blockade, prolonged apnea | Moderate |
| Opioids (e.g., Fentanyl, Morphine) | Additive respiratory and cardiovascular depression | Moderate |
| Beta-blockers (e.g., Propranolol) | Additive bradycardia and myocardial depression | Moderate |
| Rifampicin, Isoniazid | Induction of CYP2E1 may increase production of hepatotoxic metabolites | Moderate |
| MAO Inhibitors (e.g., Phenelzine) | Unpredictable BP responses; risk of hyperpyrexia | Major |