Impaired memory and behavioral performance with fentanyl at low plasma concentrations

Area of Science:

• Anesthesiology
• Pharmacology
• Neuroscience

Background:

• Fentanyl is commonly administered via continuous infusion or transdermal routes, maintaining low plasma concentrations.
• Previous cognitive effect studies have not used constant fentanyl plasma concentrations.
• Understanding fentanyl's cognitive impact at steady-state levels is crucial for patient safety.

Purpose of the Study:

• To investigate the effects of controlled, constant plasma concentrations of fentanyl on memory and psychomotor performance.
• To establish dose-dependent relationships between fentanyl levels and cognitive function.

Main Methods:

• Healthy volunteers received continuous intravenous fentanyl infusions at target plasma concentrations of 1, 1.5, and 2.5 ng/mL.
• A battery of memory and psychomotor tests were administered at each concentration and during the recovery phase.
• Pharmacokinetic modeling (IV-SIM) was used to simulate infusion profiles.

Main Results:

• Progressive decline in verbal learning, delayed recognition, and spontaneous recall with increasing fentanyl concentrations (P < 0.03).
• Fentanyl > 2.5 ng/mL caused 15%-30% performance decrement in psychomotor tests.
• Lower concentrations (< 2.25 ng/mL) had minimal effects, except for critical flicker fusion frequency.
• Significant sedation and nausea were reported; euphoria was not observed.

Conclusions:

• Constant intravenous fentanyl infusions impair cognitive functions, including memory and psychomotor performance, in a dose-dependent manner.
• Even at concentrations below 2.25 ng/mL, fentanyl can affect specific cognitive domains like critical flicker fusion.
• Fentanyl administration is associated with significant sedation and gastrointestinal side effects like nausea and emesis.