Final answer:
The offset of effects of a bolus of propofol is primarily due to redistribution, where the drug moves from the brain to other tissues with lower blood flow.
Step-by-step explanation:
The process responsible for the offset of effects of a bolus of propofol is B. Redistribution. After the initial administration, propofol causes a rapid-onset effect due to its high lipid solubility, allowing quick entry into the brain. However, this effect is short-lived as the drug quickly redistributes from the brain to other tissues with lower blood flow, such as muscle and fat. Redistribution decreases the concentration of propofol in the brain, leading to a decrease in its effects. Factors like plasma protein binding and metabolic enzymes can influence the pharmacokinetics of the drug, but redistribution is the primary reason for the rapid offset of propofol's effects after a single bolus dose.