Extradural morphine: influence of adrenaline admixture

Area of Science:

• Anesthesiology
• Pharmacology
• Neurosurgery

Background:

• Extradural morphine is used for postoperative analgesia.
• Adrenaline's effect on extradural morphine pharmacokinetics and analgesia is not fully understood.

Purpose of the Study:

• To investigate the influence of adrenaline on extradural morphine analgesia and pharmacokinetics.
• To determine if adrenaline affects morphine concentrations in plasma and cerebrospinal fluid (CSF).

Main Methods:

• A double-blind study involving 14 thoracotomy patients.
• Morphine (2 mg) administered extradurally, with or without adrenaline (50 micrograms).
• Serial plasma and CSF samples collected for morphine concentration analysis; postoperative analgesia assessed by analgesic requirements.

Main Results:

• Plain extradural morphine showed significantly higher concentrations in CSF than plasma (peak 22x, elimination 150x).
• Area Under the Curve (AUC) in CSF was 162x greater than in plasma.
• Adrenaline increased variability but did not significantly alter CSF or plasma morphine concentrations.
• Analgesia duration correlated with CSF morphine AUC and peak concentrations (P < 0.05).

Conclusions:

• Adrenaline co-administration with extradural morphine did not significantly change morphine pharmacokinetics or plasma levels.
• The duration of extradural morphine analgesia is directly related to its concentration in the CSF.