Fentanyl and morphine

Regarding opioids, which one of the following statements is CORRECT?

Compared to fentanyl, morphine has

a) A higher lipid solubility, a lower potency and a higher proportion bound to

plasma protein

b) A lower lipid solubility, a higher potency and a higher proportion bound

to plasma protein

c) A higher lipid solubility, a higher potency and a lower proportion bound to

plasma protein

d) A lower lipid solubility, a lower potency and a higher proportion bound to

plasma protein

e) A lower lipid solubility, a lower potency and a lower proportion bound

to plasma protein

Answer: e

Explanation

Morphine and fentanyl are drugs commonly used in UK anaesthesia. A candidate at

Final FRCA level should understand their pharmacology inside out. Fentanyl is more

lipid soluble than morphine and therefore crosses the blood–brain barrier more easily.

It is about 100 times more potent than morphine and is 80 to 95% plasma protein bound

compared to 20 to 40% for morphine.