Which statement about alfentanil is true?

Which statement about alfentanil is true?

• A. It has lower potency than fentanyl.
• B. It has a slower onset compared to fentanyl.
• C. CYP450 is not involved in alfentanil metabolism.
• D. It has a larger volume of distribution than fentanyl.

Answer: (A)

Alfentanil is less potent than fentanyl, so a larger dose of alfentanil is needed to achieve the same analgesic effect as fentanyl. Potency reflects the amount required for a given effect; fentanyl’s high potency means small doses produce strong analgesia, while alfentanil, though very fast-acting, requires higher milligram amounts for equivalent effect. Alfentanil does have a very rapid onset, often faster than fentanyl, due to its lower pKa and a greater fraction of nonionized drug at physiological pH, which facilitates quick CNS entry. That makes the statement about slower onset incorrect. CYP450 enzymes metabolize alfentanil, particularly via CYP3A4, so the idea that CYP450 is not involved is false. Regarding volume of distribution, alfentanil generally has a smaller Vd than fentanyl because it is less lipophilic; the claim that it has a larger Vd than fentanyl is not correct.

Alfentanil is less potent than fentanyl, so a larger dose of alfentanil is needed to achieve the same analgesic effect as fentanyl. Potency reflects the amount required for a given effect; fentanyl’s high potency means small doses produce strong analgesia, while alfentanil, though very fast-acting, requires higher milligram amounts for equivalent effect.

Alfentanil does have a very rapid onset, often faster than fentanyl, due to its lower pKa and a greater fraction of nonionized drug at physiological pH, which facilitates quick CNS entry. That makes the statement about slower onset incorrect.

CYP450 enzymes metabolize alfentanil, particularly via CYP3A4, so the idea that CYP450 is not involved is false.

Regarding volume of distribution, alfentanil generally has a smaller Vd than fentanyl because it is less lipophilic; the claim that it has a larger Vd than fentanyl is not correct.