Ketamine infusions: pharmacokinetics and clinical effects

Area of Science:

• Anesthesiology
• Pharmacology
• Clinical Chemistry

Background:

• Intravenous (I.V.) ketamine infusion is used for anesthesia.
• Understanding its pharmacokinetics and clinical effects is crucial for safe administration.

Purpose of the Study:

• To evaluate the clinical effects and pharmacokinetics of ketamine administered via I.V. infusion in patients undergoing anesthesia.
• To determine ketamine and its metabolite plasma concentrations and half-life.

Main Methods:

• Ketamine anesthesia was induced and maintained with I.V. ketamine infusion, supplemented by nitrous oxide in 31 patients.
• Plasma concentrations of ketamine, nor-ketamine, and dehydro-nor-ketamine were measured using gas-liquid chromatography.
• Clinical effects, including cardiovascular parameters and respiratory function, were monitored.

Main Results:

• The average maintenance dose of ketamine was 41 ± 21 µg kg⁻¹ min⁻¹, decreasing as anesthesia progressed.
• Stable plasma ketamine concentration was 9.3 ± 0.8 µmol L⁻¹, with a recovery concentration of 2.7 ± 0.9 µmol L⁻¹.
• Ketamine's plasma half-life was 79 ± 8 min. Transient increases in arterial pressure, heart rate, and cardiac output were observed, with no post-operative respiratory depression.

Conclusions:

• Ketamine I.V. infusion provides effective anesthesia with predictable pharmacokinetics and a favorable safety profile.
• The drug demonstrates transient cardiovascular stimulation but lacks post-operative respiratory depression, making it a viable anesthetic agent.