No effect of gender or age on binding characteristics of valproic acid to serum proteins in pediatric patients with epilepsy

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.

Cerebral Cavernous Malformation: Immune and Inflammatory Perspectives

Cerebral cavernous malformation (CCM) is a type of vascular anomaly that arises due to the dyshomeostasis of brain capillary networks. In the past two decades, many advances have been made in this research field. Notably, as a more reasonable current view, the CCM lesions should be attributed to the results of a great number of additional events related to the homeostasis disorder of the endothelial cell. Indeed, one of the most fascinating concerns in the research field is the inflammatory perturbation in the immune microenvironment, which would affect the disease progression as well as the patients’ outcomes. In this work, we focused on this topic, and underlined the immune-related factors’ contribution to the CCM pathologic progression.

A population pharmacokinetic model taking into account protein binding for the sustained-release granule formulation of valproic acid in children with epilepsy

PURPOSE

The objective of this work was to develop a population pharmacokinetic model for a prolonged-release granule formulation of valproic acid (VPA) in children with epilepsy and to determine the doses providing a VPA trough concentration (C_trough) within the target range (50-100 mg/L).

METHODS

Ninety-eight children (1-17.6 years, 325 plasma samples) were included in the study. The model was built with NONMEM 7.3. The probability to obtain C_trough between 50 and 100 mg/L was determined by the Monte Carlo simulations for doses of 20, 30, 40, and 60 mg/kg/day and body weights between 10 and 70 kg.

RESULTS

A one compartment model, with first-order absorption and flip-flop parameterization and linear elimination, but taking protein binding into account, was used to describe the data. Typical values for unbound VPA clearance and distribution volume were 6.24 L/h/70 kg and 130 L/h/70 kg respectively. Both parameters were related to body weight via allometric models. The highest probability to obtain a C_trough within the target range for 10-kg children was obtained with a 40 mg/kg daily dose, whereas daily doses of 30 and 20 mg/kg were found appropriate for 20 to 30- and ≥ 40-kg children respectively. However, for these same doses, the exposure to unbound VPA could differ by 40%.

CONCLUSIONS

If the present study supports the current dose recommendations of 20-30 mg/kg/day, except for children under 20 kg, who may need higher doses, it also highlights the need for further research on the pharmacokinetics/pharmacodynamic profile of unbound VPA.

UGT1A6- and UGT2B7-related valproic acid pharmacogenomics according to age groups and total drug concentration levels

AIM

The role of UGT1A6 and UGT2B7 polymorphisms and the impact of total drug plasma concentration in valproic acid (VPA) pharmacogenomics.

PATIENTS & METHODS

A total of 134 Greek patients were recruited (76 adults). Patients were genotyped for UGT1A6 19T>G, 541A>G and 552A>C and UGT2B7 802T>C polymorphisms. Patients' demographic and clinical data were registered. Natural logarithm of concentration-to-dose ratio (CDR) was also calculated as the final outcome.

RESULTS

No significant genotype-related differences in VPA metabolism were noted among various subgroups. An increased lnCDR ratio was noted in children patients compared with adults suggesting increased metabolic capability in younger ages.

CONCLUSION

UGT1A6 and UGT2B7 genotypes were not related to significant changes in VPA metabolism, even after controlling for total drug concentration levels. Younger ages were associated with increased VPA clearance rate.

L’absence épileptique de l’enfance dont le controle nécessite plus d’un medicament

Introduction:

Absence epilepsy is the most common primary generalized epilepsy syndrome encountered in pediatric practice. Treatment is pharmacologically specific and usually successful with a single medication. The objective of this study was to identify any clinical or electroencephalographic features at initial presentation in a consecutive cohort of children with absence epilepsy that may be associated with the need for a second medication.

Methods:

A computerized pediatric neurology database (1991-2007 inclusive) was retrospectively searched for all patients with typical absence seizures, 3 Hz spike and wave on EEG and no apparent symptomatic etiology who were over the age of two years at seizure onset with at least one year of follow-up. All such children were then divided into two groups; a) those requiring a single medication for seizure control (Group 1), and b) those requiring two medications for seizure control despite optimal management with the initial medication as determined by serum drug monitoring (Group 2). Clinical and electrographic features evident at diagnosis were then contrasted between Group 1 and 2.

Results:

Seventy-five children with absence seizures were initially identified with 52 meeting the study’s inclusion and none of the exclusion criteria. Of these 52 children, 43 required a single medication for seizure control (Group 1), while 9 required two or more medications for seizure control (Group 2). A significant difference (p<0.05) was apparent between Group 1 and 2 with respect to gender (16/43 males vs 8/9 males) and mean age of diagnosis (8.19 years +/− 3.00 vs 6.06 years +/− 2.22). Age of onset of seizures, interval duration of seizures prior to treatment initiation, duration of seizures, presence of automatisms, family history, presence of co-morbid conditions and EEG findings were not found to be significantly different between the two Groups.

Conclusions:

Male gender and an earlier age of diagnosis is associated with the need for two medications for seizure control in children with absence epilepsy. This observation may suggest the need for more intensive early programmatic follow-up for young male children with newly diagnosed absence epilepsy to effect more rapid attainment of seizure control.

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

Objectives

The aim of this study was to establish the population protein binding parameters of valproic acid (VPA) in patients with epilepsy receiving VPA monotherapy and those receiving VPA combined with other antiepileptic drugs.

Methods

One hundred and thirty nine data sets from 63 Japanese patients with epilepsy were analysed. These patients were separated into two groups: VPA monotherapy and VPA combined with other binding-sensitive antiepileptic drugs, including phenytoin, clonazepam, clobazam, carbamazepine and phenobarbital (VPA polytherapy). The population protein-binding parameters of VPA were obtained by non-linear least-squares method in each group.

Key findings

The mean (95% confidence interval) dissociation constants were 38.9 µm (33.2–44.6 µm) and 36.9 µm (26.7–47.1 µm), and the numbers of binding sites were 1.36 (1.27–1.44) and 1.33 (1.19–1.47) in the monotherapy and polytherapy groups, respectively. No significant differences in the binding parameters of VPA to serum albumin were observed between the two groups.

Conclusions

The steady-state serum albumin binding of VPA in Japanese patients with epilepsy is not affected by co-administration of other antiepileptic drugs. These findings suggest that serum VPA concentration is stable at the steady state with regard to interaction by protein binding, even when other antiepileptic drugs with moderate-to-high binding properties are co-administered.

Characterization of non-linear relationship between total and unbound serum concentrations of valproic acid in epileptic children

OBJECTIVE

To establish a regression equation to properly estimate the unbound serum concentration of valproic acid (VPA) from its total serum concentration; the relationship between total and unbound serum VPA concentrations was retrospectively characterized.

METHODS

Data were obtained from the clinical examination records that were routinely archived during therapeutic drug monitoring. The screening encompassed 342 records of 108 paediatric patients whose total and unbound VPA concentrations had been determined. The relationship between total and unbound VPA concentrations was characterized according to the Langmuir equation by taking account of inter-individual variability with the nonmem program.

RESULTS

The total VPA concentration (C(t)) in the screened patients ranged from 5.5 to 179.8 microg/mL, and the unbound VPA concentration (C(f)) increased in a non-linear manner as the total VPA concentration increased. Taking account of the effects of antiepileptics concurrently administered, the VPA dissociation constant (K(d)) and maximum binding site concentration (B(m)) were 7.8 +/- 0.7 and 130 +/- 4.5 microg/mL respectively, for the regression equation, C(t) = C(f) + B(m) x C(f)/(K(d) + C(f)). An alteration in the unbound concentration was seen in patients who were treated with the combination of VPA and ethosuximide and in those who received two additional antiepileptics.

CONCLUSIONS

A regression equation for estimation of the unbound VPA concentration, based on total VPA concentration collected during routine therapeutic drug monitoring was established. Use of two additional antiepileptics and ethosuximide treatment was considered as potential factors affecting unbound VPA concentration.

Divalproex-ER pharmacokinetics in older children and adolescents

Valproic acid pharmacokinetic profile and tolerability after administration of divalproex sodium extended-release tablets was characterized in older children and adolescents. In this multiple-dose, open-label, pharmacokinetic study, the patients were divided into two age groups, 8-11 years (older children; n = 15) and 12-17 years (adolescents; n = 14). Once-daily administration of divalproex sodium extended-release tablets (doses ranged from 250 to 1750 mg) in older children and adolescents produced relatively flat plasma valproic acid concentration-time profiles over the entire 24-hour dosing interval, similar to the pharmacokinetic performance of this formulation in adults. The mean (standard deviation) oral clearance values for unbound valproic acid were 94.3 (51.8) and 82.3 (28.2) mL/h/kg and for total valproic acid were 11.2 (3.77) and 9.06 (2.03) mL/h/kg in older children and adolescents, respectively. Two patients discontinued for administrative reasons, whereas one discontinued for an adverse event (flulike syndrome). Adverse events reported by three or more patients were flu syndrome (5 patients, 17.2%) and headache (3 patients, 10.3%). Reported adverse events were generally mild to moderate in severity and similar to those reported in previous divalproex studies. This study demonstrates that in older children and adolescents, once-daily administration of divalproex sodium extended-release tablets may potentially be used to sustain plasma valproic acid concentrations within the usually accepted therapeutic ranges for various indications.

Gender- or age-related binding characteristics of valproic acid to serum proteins in adult patients with epilepsy

The aim of the present study was to determine the gender- or age-related binding characteristics of valproic acid (VPA) to serum proteins in the adult population. Serum samples examined in the study were obtained from 70 adult patients (36 males, 34 females) with epilepsy on VPA monotherapy. Their age ranged from 16 to 68 years (mean age with (SD), 37.7 (15.7) years; <45 years, n=44; >/=45 years, n=26). The in vivo population binding parameters of VPA to serum proteins and theoretical minimal unbound serum VPA fraction (Fu) were determined using an equation derived from the Scatchard equation in: (1), all; (2), male and female subgroups; and (3), younger (<45 years) and older (>/=45 years) subgroups. There was a significant difference in serum concentration of unbound VPA between male and female patients. The mean association constant (K) was 0.010 microM(-1) in all, male, and female patients. The mean total concentration of binding sites (n(Pt)) was 1453 microM for all patients, and 1561 and 1394 microM for male and female patients, respectively. The Fu was 0.064 for all patients, and 0.060 and 0.067 for male and female patients, respectively. There were no significant differences in the binding characteristics of VPA to serum proteins between the male and female groups. On the other hand, there were significant differences in the serum albumin concentration and molar concentration ratio of free fatty acids to albumin in serum between the younger and older patients. The mean value of K was 0.016 microM(-1) for the younger patients and 0.007 microM (-1) for the older patients. The mean n(Pt) was 1157 microM for the younger patients and 1703 microM for the older patients. The Fu was 0.051 for the younger patients and 0.077 for the older patients. Thus, significant differences were observed in the binding characteristics of VPA to serum proteins between the younger and older groups. Our results show that age, but not gender, has significant influences on the binding characteristics of VPA to serum proteins in our patient population.