Individual variation in response to thiopentone.

Area of Science:

• Pharmacology
• Anesthesiology
• Biochemistry

Background:

• Thiopentone is a widely used anesthetic agent.
• Understanding factors influencing its pharmacokinetics is crucial for safe and effective use.
• Patient-specific variations in protein binding can significantly alter drug disposition.

Purpose of the Study:

• To quantify dose requirement differences for thiopentone in various patient groups.
• To investigate the impact of protein binding on thiopentone pharmacokinetics.
• To elucidate potential explanations for observed inter-individual variability in thiopentone response.

Main Methods:

• Pharmacodynamic assessment of eyelash reflex.
• In vivo and in vitro studies of thiopentone's cardiovascular effects.
• Impedance cardiography for cardiac assessment.
• Compartmental analysis of serum concentration-time data.
• High-performance liquid chromatography (HPLC) for thiopentone analysis.
• Ultrafiltration and equilibrium dialysis for unbound drug measurement.
• Albumin binding assays at varying pH and temperature.

Main Results:

• Thiopentone binding in human serum is approximately 85% and relatively constant over a wide concentration range.
• Binding increases at lower drug concentrations and is pH-dependent, rising with increasing pH.
• Albumin binding is higher at reduced temperatures.
• Reduced protein binding was observed in patients with impaired kidney/liver function, elderly individuals, pregnant women, and newborns.
• This reduced binding may account for increased total body clearance and distribution volumes in kidney failure patients.

Conclusions:

• Thiopentone's protein binding is influenced by drug concentration, pH, temperature, and patient-specific factors.
• Variations in albumin binding are significant in certain patient populations.
• Reduced binding in vulnerable groups can lead to altered pharmacokinetic parameters, necessitating dose adjustments.