The duration of action of fentanyl after a single intravenous dose is approximately?

The duration of action of fentanyl after a single intravenous dose is approximately?

• A. 0.25-0.5 hour
• B. 1-2 hours
• C. 2-3 hours
• D. 0.5-1 hour

Answer: (D)

Fentanyl acts quickly because it is highly lipophilic and reaches the brain within moments, producing rapid analgesia. But the duration of that effect after a single intravenous dose is limited by redistribution of the drug away from the CNS into other tissues and by its clearance. This redistribution shortens the clinical effect even though plasma levels may linger. For a typical single IV bolus, the analgesic and sedative effects last roughly 30 to 60 minutes, so about 0.5 to 1 hour is the realistic window. The shorter estimate would understate the duration of the clinical effect, while longer estimates reflect situations like repeated dosing or infusion rather than a single bolus.

Fentanyl acts quickly because it is highly lipophilic and reaches the brain within moments, producing rapid analgesia. But the duration of that effect after a single intravenous dose is limited by redistribution of the drug away from the CNS into other tissues and by its clearance. This redistribution shortens the clinical effect even though plasma levels may linger. For a typical single IV bolus, the analgesic and sedative effects last roughly 30 to 60 minutes, so about 0.5 to 1 hour is the realistic window.

The shorter estimate would understate the duration of the clinical effect, while longer estimates reflect situations like repeated dosing or infusion rather than a single bolus.