Urine and plasma free phenytoin concentration correlation

Area of Science:

• Clinical Pharmacology
• Analytical Chemistry
• Nephrology

Background:

• Accurate monitoring of plasma free phenytoin (CPf) is crucial for effective epilepsy management.
• Current methods for CPf determination can be invasive or complex.
• A simple, noninvasive method for estimating CPf is needed.

Purpose of the Study:

• To investigate the relationship between urine phenytoin concentration (Cu) and plasma free phenytoin concentration (CPf).
• To evaluate the potential of Cu as a noninvasive marker for estimating CPf in epileptic patients.

Main Methods:

• Studied 40 epileptic patients aged 6-50 years.
• Measured Cu using gas-liquid chromatography.
• Determined CPf using equilibrium dialysis at 37°C.

Main Results:

• A strong correlation (r² = 0.876) was observed between Cu and CPf.
• Cu was generally higher than CPf.
• The correlation was not affected by patient age, urine pH, or urine flow rate.
• Renal clearance of phenytoin increased proportionally with urine flow rates.

Conclusions:

• Urine phenytoin concentration (Cu) shows significant potential as a noninvasive method for estimating plasma free phenytoin (CPf).
• This method may be valuable for therapeutic drug monitoring in epilepsy patients.
• Further studies are needed to confirm the reliability in patients with renal impairment or albuminuria.