Comparative protein binding of diazepam and desmethyldiazepam

Area of Science:

• Pharmacology
• Clinical Chemistry

Background:

• Plasma protein binding influences drug distribution and efficacy.
• Diazepam and its metabolite desmethyldiazepam are widely prescribed anxiolytics.
• Understanding age-related changes in protein binding is crucial for pharmacokinetics.

Purpose of the Study:

• To quantify the plasma protein binding of diazepam and desmethyldiazepam.
• To investigate the influence of age and albumin concentration on this binding.
• To compare the free fractions of diazepam and desmethyldiazepam.

Main Methods:

• Equilibrium dialysis was used to determine the free fraction of diazepam and desmethyldiazepam.
• Plasma samples were collected from 62 healthy volunteers across a wide age range (20-85 years).
• Correlations with age, sex, and plasma albumin concentration were analyzed.

Main Results:

• The mean free fraction for diazepam was 1.48% and for desmethyldiazepam was 2.97%, both increasing with age.
• Free fractions were negatively correlated with plasma albumin concentration.
• The free fraction of desmethyldiazepam was consistently higher than that of diazepam.

Conclusions:

• Age significantly influences the plasma protein binding of diazepam and desmethyldiazepam.
• Desmethyldiazepam exhibits a higher unbound concentration than diazepam at equivalent total plasma levels.
• These findings have implications for understanding the pharmacodynamics and dosing of these benzodiazepines, particularly in elderly populations.