Sufentanil high protein binding results in

Sufentanil high protein binding results in

• A. Higher Vd than fentanyl
• B. Similar Vd to fentanyl
• C. Lower Vd than fentanyl
• D. No effect on Vd

Answer: (C)

Volume of distribution reflects how widely a drug distributes beyond the blood. Only the unbound portion can cross capillary walls and enter tissues, so tight plasma protein binding keeps more drug in the vascular space and lowers the apparent Vd. Sufentanil binds plasma proteins very strongly, more so than fentanyl, so the unbound fraction is smaller and less drug distributes into tissues. Even though sufentanil is highly lipophilic, the dominant effect of strong protein binding is to reduce distribution into tissues compared with fentanyl, resulting in a lower Vd.

Volume of distribution reflects how widely a drug distributes beyond the blood. Only the unbound portion can cross capillary walls and enter tissues, so tight plasma protein binding keeps more drug in the vascular space and lowers the apparent Vd. Sufentanil binds plasma proteins very strongly, more so than fentanyl, so the unbound fraction is smaller and less drug distributes into tissues. Even though sufentanil is highly lipophilic, the dominant effect of strong protein binding is to reduce distribution into tissues compared with fentanyl, resulting in a lower Vd.