Which statement best explains why fospropofol has a longer onset and duration than propofol?

Which statement best explains why fospropofol has a longer onset and duration than propofol?

• A. It is a prodrug activated by alkaline phosphatase
• B. It has higher protein binding and distribution
• C. It is rapidly metabolized by hepatic enzymes to active propofol
• D. It cannot cross the blood-brain barrier

Answer: (A)

Fospropofol is a phosphate ester prodrug of propofol. It must be hydrolyzed by alkaline phosphatase in the blood to release active propofol. This activation step takes time, so the CNS effect appears later (longer onset) compared with giving propofol directly. Once activated, propofol is released gradually, producing a prolonged effect (longer duration) as the active drug is generated and clears. The other ideas don’t fit because higher protein binding or distribution wouldn’t inherently delay onset, rapid hepatic metabolism would shorten onset, and fospropofol does cross into the CNS so “cannot cross the blood-brain barrier” isn’t correct.

Fospropofol is a phosphate ester prodrug of propofol. It must be hydrolyzed by alkaline phosphatase in the blood to release active propofol. This activation step takes time, so the CNS effect appears later (longer onset) compared with giving propofol directly. Once activated, propofol is released gradually, producing a prolonged effect (longer duration) as the active drug is generated and clears. The other ideas don’t fit because higher protein binding or distribution wouldn’t inherently delay onset, rapid hepatic metabolism would shorten onset, and fospropofol does cross into the CNS so “cannot cross the blood-brain barrier” isn’t correct.