Abstract
The accuracy and precision studies and pharmacokinetic analyses for valproic acid (VPA) by using substrate-labeled fluorescent immunoassay (SLFIA method) were performed and the results obtained by SLFIA method were compared with those of gas-liquid chromatography (GLC method). Within- and between-day precision studies of SLFIA method by use of VPA spiked samples in the normal human and rabbit plasma showed a good reproducibilitywith less than 5% as coefficient of variation and there were no significant differences (p>0.05) between the measurements by GLC and SLFIA method. Good correlations between the determinations by GLC (horizontal axis) and SLFIA (vertical axis) method were obtained and the regression equation was y=0.874x+12.4 (n=77, r=0.971, p<0.001) for rabbit samples and y=0.985x+0.866 (n=38, r=0.980, p<0.001) for the samples of patients taking a VPA preparation. These mean values obtained by both of the methods were statistically identical. After a single intravenous bolus injection (VPA dose of 56-71mg/kg) in rabbits, pharmacokinetic parameters were obtained following one-compartment open model. Apparent elimination rate constant by use of SLFIA method was significantly smaller (p<0.001) than that by GLC method, but the volume of distribution by SLFIA method was significantly larger (p<0.05) than that by GLC method. On the other hand, no significant difference was observed (p>0.05) for systemic clearance. These results are reasonably understood that SLFIA method showed significantly higher values which may be due to cross-reaction in lower VPA concentration range (less than 25μg/ml) and moreover suggested significantly lower value which may be caused by the dilution of rabbit plasma samples with a protein-free buffer in higher VPA concentration range (more than 150μg/ml).
These observations showed that SLFIA method was a useful method for clinical measurement of plasma (or serum) VPA level. However, several problems on calculating pharmacokinetic parameters with rabbits with a very short half-life remained to be elucidated.
