Pharmacology Notes

The mechanism of action of propofol is poorly defined, but its main central nervous system depressant action is thought to be via gamma-amino-butyric acid (GABA) receptors at a site of action other than that of benzodiazepines and barbiturates.

Propofol is an oil at room temperature, and therefore is formulated for intravenous administration in a lipid emulsion containing soya oil and egg lecithin. After intravenous administration, the onset of action is within 30 seconds and recovery generally occurs within three to five minutes. This rapid recovery and absence of 'hangover' effects has resulted in its increasing role in procedural sedation and short-term sedation of mechanically ventilated patients, particularly in emergency medicine.

There is a wide variation in the dose required to achieve sedation or unconsciousness, therefore doses should be titrated incrementally. Patients over the age of 55 years tend to require lower doses than younger patients.

Propofol does not possess any analgesic activity. It is associated with hypotension, bradycardia, pain at the injection site and muscle excitation resulting in tremors and involuntary movements. Brief apnoea and respiratory depression requiring ventilatory support is generally more common with propofol than with midazolam/opioid combinations used in procedural sedation.