Fentanyl interacts with other drugs via hepatic CYP3A4; which statement best describes this risk?

• A. Renal excretion is the primary route and is unaffected by enzymes
• B. CYP3A4 has no influence on fentanyl levels
• C. Fentanyl is excreted unchanged in bile
• D. CYP3A4 metabolism means inhibitors or inducers can markedly alter fentanyl levels

Answer: (D)

Fentanyl's pharmacology hinges on its metabolism by the liver enzyme CYP3A4. Because this enzyme is responsible for breaking down fentanyl, anything that inhibits or induces CYP3A4 can dramatically change how much fentanyl is in the bloodstream. When a CYP3A4 inhibitor is added, fentanyl is cleared more slowly, so levels rise and the patient is at higher risk for deep sedation and potentially life-threatening respiratory depression. Conversely, a CYP3A4 inducer speeds metabolism, lowering fentanyl levels and potentially giving insufficient analgesia or causing withdrawal in dependent patients. Given fentanyl’s high potency and relatively narrow safety margin, these interactions are especially clinically important and often require dose adjustments, close monitoring, or choosing an alternative analgesic not as dependent on CYP3A4.

The other statements don’t fit because the primary route is not renal excretion, and fentanyl is not typically excreted unchanged in bile; plus CYP3A4 does influence fentanyl levels, so saying there’s no influence would be incorrect.