Critical Care Medicine-Neurologic Disorders>>>>>Analgesia, Sedation and Neuromuscular Blockade
Question 10#

Which of the following medications has the HIGHEST increase in context-sensitive half-life during a prolonged infusion?

A. Ketamine
B. Midazolam
C. Propofol
D. Dexmedetomidine
E. Fentanyl

Correct Answer is E

Comment:

Correct Answer: E

The context sensitive half-life is the time required for blood or plasma concentrations of a drug to decrease by 50% after discontinuation of the drug administered by infusion. It factors in the effects of a prolonged infusion on half-life of a drug. In the context of continuous infusions many drugs that are short acting after a single bolus have an increase in their half-life as their volume of distribution becomes saturated. The half-life of fentanyl increases to over 300 minutes after an infusion of 5 hours. The half-life of midazolam increases to between 50 and 75 minutes after an infusion of 5 hours. The half-life of dexmedetomidine increases to around 100 minutes after an infusion of 5 hours. The half-life of propofol and ketamine both increase slightly but are around 25 minutes after an infusion of 5 hours.

References:

  1. Miller RD. Miller’s Anesthesia. 8th ed.; San Diego: Churchil Livingstone; 2015:Chap 29 & 30.
  2. Iirola T, Ihmsen H, Laitio R, et al. Population pharmacokinetics of dexmedetomidine during long-term sedation in intensive care patients. Br J Anaesth. 2012;108(3):460-468.