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Determination of free valproic acid concentrations using the Amicon Micropartition MPS-1 Ultrafiltration System
Abstract:
Free valproic acid concentrations were determined using the MPS-1 ultrafiltration device marketed by Amicon with one YMB membrane per device. Valproic acid binding to the membrane was 5.6% of the free valproic acid concentration. The free valproic acid concentration increased as serial ultrafiltrate volumes were collected, suggesting that only small ultrafiltrate volumes should be collected from a large initial sample. The protein content of the ultrafiltrate was acceptable and was within the tolerances stated by Amicon. There was no significant difference between free valproic acid concentrations determined within 3 h of sample collection and those determined after storage at 4 degrees C or -20 degrees C for 1 week. There was no significant difference between free valproic acid concentrations in serum and heparinized plasma samples collected simultaneously.
Insights
Ultrafiltration accurately measures free valproic acid. Minimize ultrafiltrate volume and note that serum and heparinized plasma are interchangeable for this assay.
Area of Science:
- Pharmacokinetics
- Analytical Chemistry
- Clinical Chemistry
Background:
- Accurate determination of free valproic acid is crucial for therapeutic drug monitoring.
- Ultrafiltration is a common method for measuring free drug concentrations.
- Potential issues include drug binding to membranes and sample volume effects.
Purpose of the Study:
- To evaluate the performance of the Amicon MPS-1 ultrafiltration device for free valproic acid determination.
- To assess valproic acid binding to the YMB membrane.
- To investigate the impact of ultrafiltrate volume and sample storage on results.
Main Methods:
- Free valproic acid concentrations were measured using the Amicon MPS-1 ultrafiltration device with YMB membranes.
- Valproic acid binding to the membrane was quantified.
- Serial ultrafiltrate volumes were collected.
- Samples were stored at different temperatures for up to one week.
- Comparisons were made between serum and heparinized plasma.
Main Results:
- Valproic acid binding to the YMB membrane was 5.6%.
- Free valproic acid concentration increased with larger ultrafiltrate volumes, indicating a need for small collection volumes.
- Protein content in the ultrafiltrate was within acceptable limits.
- No significant differences were observed in free valproic acid concentrations after storage for one week at 4°C or -20°C.
- No significant differences were found between serum and heparinized plasma.
Conclusions:
- The Amicon MPS-1 device is suitable for determining free valproic acid concentrations.
- Optimizing ultrafiltration volume is important for accurate results.
- Sample storage and matrix (serum vs. plasma) do not significantly affect free valproic acid measurements.