TYK9
All of the following are true concerning propofol EXCEPT:
A. The short duration of action after a single IV bolus dose are due to a redistribution phenomenon
B. Propofol decreases cerebral blood flow (CBF)
C. Propofol's mechanism of action is through the GABA type A receptor
D. Propofol has moderate analgesic properties
E. Propofol follows a context-sensitive half life
Answer
The correct answer is D. All the other statements are true. It has NO analgesic properties. Propofol is highly protein bound in vivo and is metabolized by conjugation in the liver. Its rate of clearance exceeds hepatic blood flow, suggesting an extra-hepatic site (plasma) elimination as well. It has several mechanisms of action, both through potentiation of GABA-A receptor activity, thereby slowing the channel closing time, and also acting as a sodium channel blocker. Recent research has also suggested the endo-cannabinoid system may contribute significantly to propofol's anesthetic action and to its unique properties.
The elimination half-life of propofol has been estimated to be between 2-24 hours. However, its duration of clinical effect is much shorter because propofol is rapidly distributed into peripheral tissues (redistribution). When used for IV sedation, propofol typically wears off in minutes after a single bolus. When used as an infusion, redistribution becomes less important because the non-target tissues have become saturated as well. After infusion, the half life of propofol is mostly due to its plasma/liver metabolism and therefore its effects are extended. In practice, if you infuse propofol for about 6 hours, expect the effects to last about 30-40 minutes instead of the 8-10 minutes you are used to after a single bolus. Its use is not associated with nausea as is often seen with opioid medications and may actually be used as an anti-emetic in sub-anesthetic doses. [1]