Diphenylhydantoin: correlation between protein binding and albumin concentration

Area of Science:

• Pharmacokinetics
• Clinical Chemistry

Background:

• Diphenylhydantoin (phenytoin) is a widely used anticonvulsant medication.
• Drug binding to serum proteins, particularly albumin, influences its pharmacological activity.
• Accurate assessment of unbound drug concentrations is crucial for therapeutic drug monitoring.

Purpose of the Study:

• To investigate the relationship between serum albumin concentration and the unbound fraction of diphenylhydantoin.
• To evaluate the feasibility of graphical estimation of unbound diphenylhydantoin.
• To assess the clinical implications of altered diphenylhydantoin binding in nephrotic syndrome.

Main Methods:

• Retrospective analysis of patient data.
• Graphical estimation techniques.
• Comparison of unbound drug fractions between patient groups.

Main Results:

• A significant inverse correlation was observed between diphenylhydantoin unbound fraction and serum albumin concentration.
• Graphical estimation provided accurate assessment of unbound diphenylhydantoin.
• Patients with nephrotic syndrome exhibited approximately double the unbound fraction of diphenylhydantoin.
• Despite increased unbound fraction, absolute unbound drug concentrations remained stable due to increased volume of distribution and plasma clearance.

Conclusions:

• Serum albumin concentration is a key determinant of diphenylhydantoin binding.
• Graphical estimation is a viable method for determining unbound diphenylhydantoin levels.
• Compensatory pharmacokinetic changes in nephrotic syndrome maintain stable unbound drug concentrations, potentially obviating dose reduction.