the lungs. The remaining 20% is lower concentration is usually HALOSIN metabolized in the liver by oxidative and most suitable for elderly under hypoxic conditions, reductive patients. Indications pathways. The main metabolites are Halothane is a volatile anaesthetic which trifluoroacetic acid, bromide and Interaction is suitable for the induction and chloride salts (via the oxidative Increased risk of ventricular maintenance of anaesthesia for all types pathway) and fluoride salts (via the dysrhythmias with epinephrine. of surgery and in patients of all ages. reductive pathway). The concentrations Increased risk of malignant of metabolites peak 24 hours post- hyperthermia with suxamethonium. Therapeutic Class operatively and are eliminated by renal Prolonged recovery from anaesth with General (Inhalation) anesthetics excretion during the following week. concurrent use of ketamine for induction. May potentiate response to Pharmacology Dosage & Administration non-depolarising muscle relaxants, When inhaled, Halothane is absorbed A number of anaesthetic vaporisers hypotensive agents (e.g. hexamethonium through the alveoli into the bloodstream. specially designed for use with bromide, trimetaphan camsilate). In the bloodstream, Halothane circulates Halothane are available. Open, semi- through the body to the principal site of open, semi-closed and closed circuit Contraindications action, the brain. Here Halothane causes systems have all been used with good Halothane can induce liver damage; a progressive depression of the central results. however, the incidence of severe liver nervous system, beginning with the damage (jaundice, which may lead to higher centers (cerebral cortex) and For induction of anaesthesia: hepatic failure as a consequence of spreading to the vital centers in the massive hepatic cell necrosis) is medulla. This depression is reversible. unknown. The risk of developing hepatic However, its mode of action, like all ▪ Adult: A concentration of 2-4% failure appears to be increased by anaesthetic agents, is unknown. Halothane in Oxygen or Nitrous repeated exposure. Although short Oxide may be used. intervals of time between exposures are Halothane has a relatively low solubility ▪ Children: A concentration of 1.5- likely to increase the risk of in blood and therefore alveoli/blood 2% Halothane in Oxygen or hepatotoxicity, even long intervals concentrations equilibrate rapidly. The Nitrous Oxide is used. between exposures may triexponential decline in Halothane For maintenance of anaesthesia: not eliminate the risks, since some blood concentrations following the end patients have developed severe of administration is thought to represent reactions following Halothane given distribution into three compartments; ▪ Adults and children: A many years after the previous the vessel rich group (brain/heart/liver), concentration of 0.5-2% is exposures. On the information which is the musculature and adipose tissue. usually required for available at the present time, it is Approximately 80% of the inhaled maintenance of anaesthesia. The advised that the following Halothane is eliminated unchanged by precautions be taken anaesthesia with inhalation agents Storage Conditions during early pregnancy, except where Bottles of Halothane must be securely such use is essential. closed and stored in a cool dry place, ▪ A careful anaesthetic history protected from light. Halothane must be should be taken prior to use, to Lactation: There are no well controlled kept in the original container until determine previous exposure studies with Halothane in lactating immediately prior to its use. and previous reactions following women. Halothane has been detected in Halothane anaesthesia. breast milk of lactating women, but the Whilst in the liquid phase, ▪ Repeated exposure to Halothane effect of Halothane on breast feed Halothane must not be diluted or within a period of at least 3 neonates has not been established. contaminated; however, in the vapour months should be avoided However, Halothane has been in wide phase it may be administered together unless there are overriding use for over 30 years without apparent with Oxygen or a mixture of Nitrous clinical circumstances. ill consequence Oxide and Oxygen. ▪ History of unexplained jaundice and pyrexia in a patient following Precautions & Warnings exposure to Caution should be exercised during ▪ Halothane is a contraindication administration of adrenaline to patients to its future use in that patient anaesthetised with Halothane as unless absolutely essential. dysrhythmias may be precipitated. For ▪ Patients should be informed if this reason the dose of adrenaline they have developed a reaction should be restricted and beta-receptor possibly related to Halothane antagonists administered if necessary. anaesthesia; such patients Ensure adequate room ventilation when should be provided with a Halothane is being used. Keep the medical alert card stating the concentration of Halothane in air as low problem. as possible.

Side Effects Effect on ability to drive or operate Post-op nausea, vomiting, and shivering; machinery: Patients should be advised resp depression, hypotension, skeletal that performance at skilled tasks, such muscle relaxation, bradycardia. as driving and operating machinery, may be impaired for some time after general Pregnancy & Lactation anaesthesia. Category C: Although the data from experimental investigations in animals Accidental ingestion: Cases of ingestion cannot be directly related to man, it must be treated symptomatically. would be prudent to avoid general