Measured Context-sensitive Half-times of Remifentanil and Alfentanil

Abstract

The measured context-sensitive half-times were in close agreement with the context-sensitive half-times previously modelled for these drugs. The results of this study confirm the value of the context-sensitive half-time in describing drug offset compared to the terminal elimination half-life.

Decreased duration of mechanical ventilation when comparing analgesia-based sedation using remifentanil with standard hypnotic-based sedation for up to 10 days in intensive care unit patients: a randomised trial [ISRCTN47583497]

“…The context-sensitive half-time of remifentanil is constant and independent of duration of drug administration when administered for up to 6 hours [3], but does this situation change when remifentanil is given for days rather than hours? One study looked at the pharmacodynamic offset of remifentanil at various time points over 3 days in ICU patients and found that the offset time was constant over this period [5].…”

“…Remifentanil is metabolised by non-specific plasma esterases and is therefore independent of organ function [2]. Remifentanil is rapidly metabolised and has a context-sensitive half-time of about 2 to 3 min that is independent of duration of infusion [3]. These features of remifentanil make it an ideal agent for use in critically ill patients.…”

Tissue Distribution and Pharmacodynamics: A Complicated Relationship

“…The reason for the short duration of effect is the redistribution of thiopental from highly perfused tissues, particularly the CNS, to other tissues [258]. Clinical studies with anesthetic drugs revealed that the elimination half-life often failed to predict the loss of anesthetic effect (recovery from anesthesia) [259,260]. For example, the half-life of loss of anesthetic effect was 5 and 50 min for remifentanil and alfentanil, respectively, while the corresponding elimination half-lives were 20 and 110 min [259].…”

“…Clinical studies with anesthetic drugs revealed that the elimination half-life often failed to predict the loss of anesthetic effect (recovery from anesthesia) [259,260]. For example, the half-life of loss of anesthetic effect was 5 and 50 min for remifentanil and alfentanil, respectively, while the corresponding elimination half-lives were 20 and 110 min [259]. Sufentanil, with an elimination half-life of 577 min, had a shorter half-life of anesthetic recovery compared to alfentanil, whose half-life of loss anesthesia was 50 min.…”

Pharmacology of Sedation Agents and Reversal Agents

“…All opioids depress the central nervous, respiratory and cardiovascular system (particularly meperidine), and they increase the intrabiliary pressure, decrease gastric motility and cause nausea/vomiting and constipation. Though sufentanil, alfentanil and remifentanil are superior to fentanyl, fentanyl is a good choice with the less cost [8,9]. …”