What percentage of the initial IV fentanyl dose undergoes first-pass uptake into the lungs?

What percentage of the initial IV fentanyl dose undergoes first-pass uptake into the lungs?

• A. 25%
• B. 75%
• C. 50%
• D. 90%

Answer: (B)

Fentanyl’s very high lipophilicity and the lungs’ high blood flow cause a large portion of an IV bolus to be taken up during the first pass through the pulmonary circulation. About three-quarters of the initial dose is sequestered in the lungs on this first pass, so only roughly a quarter remains to enter systemic circulation immediately. This pulmonary extraction helps explain the rapid distribution and onset of fentanyl, while the rest will redistribute from the lungs to other tissues over time.

Fentanyl’s very high lipophilicity and the lungs’ high blood flow cause a large portion of an IV bolus to be taken up during the first pass through the pulmonary circulation. About three-quarters of the initial dose is sequestered in the lungs on this first pass, so only roughly a quarter remains to enter systemic circulation immediately. This pulmonary extraction helps explain the rapid distribution and onset of fentanyl, while the rest will redistribute from the lungs to other tissues over time.