Halothane

Halothane is an inhalation anaesthetic used once.

1. HALOTHANE Submitted by, Vysakh Mohan M 13-BVM-42

2. HALOTHANE INTRODUCTION General anaesthetic Volatile liquid inhalation anaesthetic Molecular formula – CF 3 CHClBr IUPAC Name – 2-bromo-2-chloro-1,1,1-trifluoroethane Brand Name – Fluothane Induction and maintenance anaesthetic agent

3. HALOTHANE PHYSICAL AND CHEMICAL PROPERTIES Volatile Heavy liquid (Specific gravity – 1.87) Boiling point – 50.2 C Vapour pressure – 243 mmHg at 20 C Molecular Weight – 197.4   u Decomposes when exposed to light (Amber coloured bottles and addition of thymol ) Non-explosive and non-inflammable

4. HALOTHANE MINUMUM ALVEOLAR CONCENTRATION/MAC * Dogs – 1.87 Cats – 1.19 Cattle – 0.76 Horses – 0.88 Humans – 0.76

5. HALOTHANE DOSE Induction (Halothane alone) All species : 2.0 – 4.0% (of inspired air) Maintenance (Halothane alone) Small animals : 0.5 – 1.5% Large animals : 1.0 – 2.0%

6. HALOTHANE PHARMACOKINETICS Rapidly absorbed and rapidly excreted through lungs 20% : Biotransformation in liver and excreted through lungs 60% : Excreted unchanged through lungs 20% : Excreted via other routes, either unchanged or metabolised and stored in body for many hours to days

7. HALOTHANE ADVESE EFFECTS Vasodilatation, hypotension, shivering and tremors on recovery Malignant hyperthermia Cardiac arrhythmias Cardiopulmonary depression and cardiac arrest

8. HALOTHANE CONTRAINDICATIONS AND PRECAUTIONS Not used for pig breeds like Poland China and Pietrain Used with caution in animals with increased CSF, head injury, etc. Not used in animals having problems after previous halothane exposure

9. HALOTHANE CLINICAL USES AND ADMINISTRATION Capable of induction and maintenance of anaesthesia without assistance from other CNS depressants Used in a closed rebreathing system with precision thermo-stable or thermo-compensated, calibrated vapourisers Open and semi-open systems are used only in case of very small dogs, cats and laboratory animals

10. HALOTHANE RELATED SUBSTANCES Enflurane , isoflurane and sevoflurane . Incidence of  hepatic reaction with these agents is lower L ower blood solubility r esulting in faster induction of and recovery from anaesthesia

11. HALOTHANE – RELATED SUBSTANCES Attempts to find anesthetics with less metabolism led to halogenated ethers such as enflurane and isoflurane The incidence of hepatic reactions with these agents is lower. The exact degree of  hepatotoxic  potential of enflurane is debated, although it is minimally metabolized. Isoflurane is essentially not metabolized and reports of associated liver injury are quite rare. Small amounts of  trifluoroacetic acid can be formed from both halothane and isoflurane metabolism and possibly accounts for cross sensitization of patients between these agents. The main advantage of the more modern agents is lower blood solubility, resulting in faster induction of and recovery from anaesthesia .

12. HALOTHANE AVAILABILITY Available as a volatile liquid, at 30, 50, 200, and 250 ml per container I n many developed nations is not available having been displaced by newer agents.