Alfentanil characteristics: which statement is true?

Alfentanil characteristics: which statement is true?

• A. Has a more rapid onset of action compared to fentanyl
• B. Has a longer duration of action compared with fentanyl
• C. Is more potent than fentanyl
• D. Undergoes little hepatic metabolism

Answer: (A)

Onset of action for opioids depends on how quickly the drug crosses into the brain. Alfentanil is a fentanyl analogue designed to act very rapidly. Its pharmacokinetic profile includes a high free (unbound) fraction and fast diffusion across the blood–brain barrier, so when given IV it produces analgesia sooner than fentanyl. That rapid CNS entry translates into a quicker onset of effect, which is why this statement is true. In contrast, the idea that it lasts longer than fentanyl isn’t correct—the duration is shorter because alfentanil is cleared more rapidly from the body and redistributes quickly to less active compartments. It also isn’t true that it undergoes little hepatic metabolism; it is actively metabolized in the liver by CYP3A4 pathways, contributing to its short duration. And it isn’t more potent than fentanyl; alfentanil is less potent, requiring a higher dose to achieve comparable effects. Thus, the best truth about alfentanil among these points is that it has a more rapid onset of action compared with fentanyl.

Onset of action for opioids depends on how quickly the drug crosses into the brain. Alfentanil is a fentanyl analogue designed to act very rapidly. Its pharmacokinetic profile includes a high free (unbound) fraction and fast diffusion across the blood–brain barrier, so when given IV it produces analgesia sooner than fentanyl. That rapid CNS entry translates into a quicker onset of effect, which is why this statement is true.

In contrast, the idea that it lasts longer than fentanyl isn’t correct—the duration is shorter because alfentanil is cleared more rapidly from the body and redistributes quickly to less active compartments. It also isn’t true that it undergoes little hepatic metabolism; it is actively metabolized in the liver by CYP3A4 pathways, contributing to its short duration. And it isn’t more potent than fentanyl; alfentanil is less potent, requiring a higher dose to achieve comparable effects.

Thus, the best truth about alfentanil among these points is that it has a more rapid onset of action compared with fentanyl.