Pharmacology Notes

Thiopentone is a barbiturate, and therefore potentiates the inhibitory effects of gamma amino butyric acid (GABA) in the central nervous system. After a single dose, unconsciousness occurs approximately 10 to 20 seconds after injection and recovery occurs after 5 to 10 minutes. Rapid recovery is largely due to redistribution rather than hepatic metabolism. Due to interindividual variation, doses are titrated incrementally to effect. Intravenous cannulae must be thoroughly flushed after administration of thiopentone due to the risk of precipitation, especially in combination with the neuromuscular blocking agents. Bronchospasm may occur; therefore thiopentone is best avoided in asthma. Respiratory depression may be prolonged in myasthenia gravis and muscular dystrophy. Hypotension and myocardial depression are common. Patients may notice a 'garlic' taste during induction. Thiopentone is cerebroprotective, which can be useful in head injury and status epilepticus. Thiopentone should not be used for short procedures where a patient may be discharged rapidly, as full recovery may take up to 24 hours. Extravasation can result in local tissue necrosis.