No effect of co-administered antiepileptic drugs on in-vivo protein binding parameters of valproic acid in patients with epilepsy

Slipped capital femoral epiphysis in a 5-year-old boy with cerebral palsy on valproic acid and levetiracetam for epilepsy: a case report

This study presents a rare case of unilateral slipped capital femoral epiphysis treated surgically in a 5-year-old boy with cerebral palsy who was born at 27 weeks' gestation and developed grade III intraventricular haemorrhage and periventricular leucomalacia and was on antiepileptic drugs, including valproic acid and levetiracetam for >3 years. The patient had no history of endocrine, renal, and significant familial diseases.

A novel method for predicting the unbound valproic acid concentration

In this study, we constructed a prediction formula for unbound valproic acid (VPA) concentration that was more accurate and widely applicable than previously reported formulae. A total of 136 datasets from 75 patients were analyzed retrospectively. The median of free fraction of VPA was 0.16 (interquartile range: 0.07; range: 0.07-0.45). The parameter that combined total VPA concentration (C_tVPA) and serum albumin (SA), (C_tVPA [μM] - 2 × SA [μM]), was significantly related to the free fraction of VPA (r = 0.76, p < 0.001). We constructed a combined parameter-based prediction formula for unbound VPA concentration. Analysis using external datasets from patients without severe renal failure showed that the prediction errors of the unbound VPA concentration were lower than those of previously reported formulae. Although the previous formulae showed large prediction errors, especially in the specific range of C_tVPA values, the constructed formula showed a weak trend with C_tVPA or SA. The formula based on (C_tVPA [μM] - 2 × SA [μM]) had high prediction accuracy and wide applicability in predicting the unbound VPA concentration in patients without severe renal failure.

Determination of unbound valproic acid in plasma using centrifugal ultrafiltration and gas chromatography:Application in TDM

AIM

In order to monitor the free concentration of VPA in plasma, a simple and rapid method needs to be developed.

METHODS

The free fraction of VPA in plasma was obtained by centrifugal ultrafiltration (CF-UF) devices. Cyclohexanecarboxylic acid was used as internal standard. Valproate in plasma was converted to VPA by sulphuric acid acidification, and dichloromethane was used as solvent for extraction. Nitrogen was the carrier gas, the samples were separated by capillary column, and the flame ionization detector was used to detect VPA fragment ions for quantitative analysis.

RESULTS

The assay had good specificity and stability. The linear range of the assay was 0.56-28.11 mg/L. The intra-day and inter-day precision (RSDs) of the assay were all within 15%, and the accuracy (RE) was 2.58%. The recoveries of VPA with three different concentrations were 102.03 ± 1.05, 101.45 ± 2.08 and 102.58 ± 3.38. The results of therapeutic drug monitoring (TDM) in pediatric inpatient group and outpatient group showed significant differences between the two groups (P < 0.001).

CONCLUSION

This assay has low cost and good analytical performance, so it can be developed into a routine TDM method of unbound VPA. We recommend the monitoring of unbound VPA concentration in pediatric inpatients during clinical use of VPA.

The survival effect of valproic acid in glioblastoma and its current trend: a systematic review and meta-analysis

Glioblastoma (GBM) can often present with seizure. Attempts have been made to associate the use of anti-epileptic medication valproic acid (VPA) in standard of care management with survival benefit in the past; however, results to date have been conflicting, and most likely subjected to historical bias. This study aimed to quantify the overall survival (OS) effect of VPA in patients with GBM based on the current literature, and identify potential trend-modifying covariates. Searches of 7 electronic databases from inception to April 2018 were conducted following the appropriate guidelines. Hazard ratios (HRs) derived from Cox proportional hazard models, and mean differences (MDs), were analyzed using the random effects model. Meta-regression was used to identify potential trend-modifying covariates. Seven retrospective cohort studies satisfied selection criteria describing 2181 primary GBM diagnoses, with 534 (24%) receiving VPA in their treatment. Overall, VPA was shown to confer a statistically significant OS advantage (HR, 0.71; 95% CI, 0.56-0.91; p < 0.01) compared to the control group by up to 2.4 months (95% CI, 1.51-3.21; p < 0.01). However, upon meta-regression, this survival advantage as inferred by HRs trended towards the null in newer studies (slope, 1.15; p = 0.02) or in studies with older participants (slope, 1.13; p = 0.02). A similar result was seen with MDs. Based on the literature to date, VPA was significantly associated with better OS in GBM patients by 2.4 months when managed by current standard of care. However, this effect was particularly emphasized among older studies or studies conducted in younger participants indicating the need to exercise caution in assuming generalizability of the pooled effect. Overall, there is considerable bias risks in the current interpretation of the literature, and larger, prospective studies are required for validating our findings.

Population pharmacokinetics of valproic acid in epileptic children: Effects of clinical and genetic factors

Valproic acid (VPA) is a first-line anti-epileptic drug that is used in the treatment of generalized and partial seizures. Gene variants had been proved to influence the pharmacokinetics (PK) of VPA and contribute to its inter-individual variability (IIV). The aim of this study was to systematically investigate the effects of candidate gene variants (CYPs, UGTs, ABC transporters, and nuclear receptors) on VPA PK in Chinese children with epilepsy. A total of 1065 VPA serum trough concentrations at steady state were collected from 264 epileptic pediatric patients aged 3 months to 16 years. The population pharmacokinetic (PPK) model was developed using a nonlinear mixed effects modelling (NONMEM) approach. For the final PPK model, the oral clearance (CL/F) of VPA was estimated to be 0.259 L/h with IIV of 13.3%. The estimates generated by NONMEM indicated that the VPA CL/F was significantly influenced by patient body weight (increased by an exponent of 0.662), co-administration with carbamazepine (increased CL/F by 22%), and daily dose of VPA (increased by an exponent of 0.22). CL/F in patients with the LEPR rs1137101 variant (668 AG and GG genotypes) was much lower than in patients with the AA genotype (17.8% and 22.6% lower, respectively). However, none of the CYPs or UGTs gene variants was found to influence the PK of VPA in this study. Evaluation by bootstrap and normalized prediction distribution error (NPDE) showed that the final model was stable. The predictive performance was evaluated by goodness-of-fit (GOF) plots and visual predictive checks (VPC), and the results indicated satisfactory precision. Our model suggests a correlation between VPA CL/F and LEPR rs1137101 variants, which might be beneficial in the context of individual dose optimization.

Valproic acid disrupts the biomechanics of late spinal neural tube closure in mouse embryos

Failure of neural tube closure in the early embryo causes neural tube defects including spina bifida. Spina bifida lesions predominate in the distal spine, particularly after exposure to the anticonvulsant valproic acid (VPA). How VPA specifically disturbs late stages of neural tube closure is unclear, as neurulation is usually viewed as a uniform 'zippering' process along the spine. We recently identified a novel closure site ("Closure 5") which forms at the caudal extremity of the mouse posterior neuropore (PNP) when completion of closure is imminent. Here we investigated whether distal spina bifida in VPA-exposed embryos involves disruption of Closure 5. Exposure of E8.5 mouse embryos to VPA in whole embryo culture had marked embryotoxic effects, whereas toxic effects were less pronounced in more developmentally advanced (E9) embryos. Only 33% of embryos exposed to VPA from E9 to E10.5 achieved PNP closure (control=90%). Short-term (8h) VPA treatment diminished supra-cellular F-actin cables which normally run along the lateral neural folds, and prevented caudal PNP narrowing normally characteristic of Closure 5 formation. Laser ablation of Closure 5 caused rapid neuropore widening. Equivalent ablations of the caudal PNP in VPA treated embryos resulted in significantly less widening, suggesting VPA prevents formation of Closure 5 as a biomechanically active structure. Thus, VPA exposure prevents morphological and biomechanical conversion of the caudal extreme of the PNP during late spinal closure. Closure 5 facilitates neural fold apposition when completion of closure is imminent, such that its disruption in VPA-exposed embryos may lead to distal spina bifida.

Comparison of free fraction serum valproic acid concentrations between inpatients and outpatients

PURPOSE

The differences in free fraction serum valproic acid concentrations between inpatients and outpatients were compared, and factors associated with therapeutic discordance were evaluated.

METHODS

This retrospective, single-center, cross-sectional study included patients with both a free and a total valproic acid concentration drawn within 30 minutes of each other between January 7, 2003, and June 1, 2011. Serum valproic acid concentrations were stratified by admission status (inpatient versus outpatient). In the primary analysis, for patients who had multiple paired concentrations drawn, one free valproic acid level and one total valproic acid level (i.e., one pair) were chosen at random for each inpatient. Information regarding patient demographics, laboratory data, and concomitant medication therapy was collected. Single and multivariable logistic regressions were performed to determine the odds of therapeutic discordance.

RESULTS

During the study period, inpatient concentrations were measured in 220 patients, and outpatient concentrations were measured in 41 patients. The median total valproic acid concentration in the inpatient group was significantly lower than that in the outpatient group (54 μg/mL versus 83 μg/mL, p < 0.001). The median free fraction of inpatient levels was nearly twice as high as that of outpatient levels (28.8% versus 15.5%, p < 0.001). Levels drawn in inpatients were therapeutically discordant 63% of the time compared to only 19% in outpatients (p < 0.001). Multivariable logistic regression identified low albumin as an independent risk factor for therapeutic discordance.

CONCLUSION

The median free fraction of valproic acid was significantly higher in inpatients than in outpatients. Low albumin concentration was a predictor of discordance between free and total valproic acid concentrations.

Correlation between plasma ammonia level and serum trough concentration of free valproic acid in patients with epilepsy

Therapeutic drug monitoring of valproic acid (VPA) is essential to prevent toxicity, but the correlation between plasma ammonia level and serum VPA concentration remains unclear. We examined the correlation of plasma ammonia level with VPA dose and serum trough concentrations of total and free VPA in Japanese patients with epilepsy. Thirty-eight data sets from 19 Japanese patients with epilepsy were analyzed. The relations of VPA dose and serum total and free VPA concentrations with plasma ammonia level, and the breakpoints of VPA parameters predicting hyperammonemia (plasma ammonia higher than 60 µmol/L) were analyzed. A significant positive correlation was observed between plasma ammonia level and VPA dose (r(s)=0.56, p=0.00062), serum trough total VPA concentration (r(s)=0.55, p=0.00086) and serum trough free VPA concentration (r(s)=0.58, p=0.00041). The breakpoints predicting hyperammonemia were VPA dose of 30.4 mg/kg, serum trough total VPA concentration of 90.9 µg/mL, and serum trough free VPA concentration of 8.65 µg/mL, with impurity reductions at 1.35, 1.35 and 2.02, respectively. These findings suggest that serum trough concentration of free VPA is the most reliable predictor for hyperammonemia, and that the risk of developing hyperammonemia may increase in patients with serum trough free VPA concentrations higher than 8.65 µg/mL.