Other Names/Brands

Fluothane, Halothane, Halosin

Mechanism of Action

Halothane is an inhalation anesthetic that works by depressing the central nervous system (CNS), particularly the brain and spinal cord, to produce sedative, analgesic, and unconsciousness effects. Halothane increases the activity of the inhibitory neurotransmitter GABA at GABA-A receptors, thereby inhibiting neuronal excitability through the influx of chloride ions.

Furthermore, halothane blocks NMDA receptors, which play a role in the transmission of glutamate (an excitatory neurotransmitter), supporting the analgesic effect. In the spinal cord, it suppresses pain signals and motor activity, resulting in muscle relaxation. Other systemic effects include decreased blood pressure due to peripheral vasodilation and respiratory depression.

Approximately 20% of halothane is metabolized in the liver, with the remainder excreted through the lungs. Its anesthetic effect is rapid due to its high lipid solubility, which allows rapid penetration into the CNS.

Indications

Halothane is used for the induction and maintenance of general anesthesia in both children and adults in a variety of surgical procedures. It is effective for minor to major operations, including abdominal, orthopedic, and neurosurgical procedures. Halothane is widely used in children because it is relatively non-irritating to the airways and has a rapid onset of action.

Contraindications

Halothane is contraindicated in patients with a history of hypersensitivity or previous hepatotoxicity due to halothane (halothane hepatitis). Halothane should also not be used in patients with severe liver impairment or a history of malignant hyperthermia, a serious condition resulting from an abnormal response to anesthetics. Use in patients with cardiac disease (e.g., arrhythmias or heart failure) should be considered with caution due to the potential for arrhythmias triggered by increased sensitivity to catecholamines.

Side Effects

Common side effects include hypotension, bradycardia, and respiratory depression. Some serious side effects include halothane hepatitis, which can be fatal, especially after repeated exposure, and malignant hyperthermia, characterized by a drastic increase in body temperature and muscle rigidity. Halothane can also trigger cardiac arrhythmias, especially when combined with sympathomimetic drugs such as adrenaline.

Preparations and Dosage

Halothane is available as a pure inhalation solution vaporized through a vaporizer. Dosage is determined by the concentration in the inspired gas (percent volume), not milligrams. For induction, 0.5%–3% is used; for maintenance, 0.5%–1.5%. Doses are lower in children due to their greater sensitivity.

Safety of Drugs

The use of halothane requires close monitoring due to the risk of hepatotoxicity and cardiac complications. In many countries, its use has declined and been replaced by safer anesthetic agents such as sevoflurane. The FDA classifies halothane as pregnancy category C, so its use in pregnant women requires careful consideration of the benefits and risks.

Drug Interactions

Halothane interacts with sympathomimetics (epinephrine), MAOIs, tricyclic antidepressants, and non-depolarizing muscle relaxants, which can potentiate side effects, particularly on the heart and liver. Concomitant use with N₂O potentiates the anesthetic effect. Also be aware of interactions with other hepatotoxic drugs, such as paracetamol and isoniazid.

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