The influence of old age and enzyme inducing comedication on the pharmacokinetics of valproic acid at steady-state: A case-matched evaluation based on therapeutic drug monitoring data

Genetic and non-genetic factors influencing the therapeutic response of valproic acid in pediatric epileptic patients

AIMS

Considerable inter-individual variability in the efficacy of valproic acid (VPA) has been reported, with approximately 20-45% of patients failing to achieve satisfactory seizure control after VPA monotherapy. The aim of this study was to investigate the influence of non-genetic and genetic factors on 12-month VPA-response in a cohort of 194 pediatric patients.

MATERIALS & METHODS

Trough concentrations were determined, and a panel of 48 variants located in pharmacokinetic and pharmacodynamic gene were genotyped.

RESULTS

Aetiology was highlighted as a significant factor for the response to VPA. Specifically, patients with idiopathic epilepsy demonstrated poorer 12-month outcomes (p < 0.001). Trough VPA concentrations did not significantly affect outcomes. Marginal association was found between VPA efficacy and the following genetic variants: GABRA1 rs10068980 (p = 0.02), SLC16A1 rs7169 (p = 0.02), ABCC2 rs1885301 (p = 0.092), ACADM rs1251079 (p = 0.061) and GABRA1 rs6883877 (p = 0.085), as indicated by Fisher's exact test. A significant cumulative effect of two genetic factors (GABRA1 rs10068980 and SLC16A1 rs7169) was observed after a multiple logistic analysis, with ORs of 2.828 (1.213, 6.594) and 4.066 (1.148,14.398), respectively.

CONCLUSION

Our study indicated that GABRA1 rs10068980 and SLC16A1 rs7169 might serve as potential biomarkers for predicting the 12-month VPA treatment outcomes in pediatric patients with epilepsy.

Population Pharmacokinetics of Valproic Acid in Pediatric and Adult Caucasian Patients

(1) Background: The aim of this study was to explore the valproic acid (VPA) pharmacokinetic characteristics in a large population of pediatric and adult Caucasian patients and to establish a robust population pharmacokinetic (PopPK) model. (2) Methods: A total of 2527 serum VPA samples collected from 1204 patients included in a therapeutic drug monitoring program were retrospectively analyzed. Patients were randomly assigned to either a model development group or an external evaluation group. PopPK analysis was performed on 1751 samples from 776 patients with NONMEM using a nonlinear mixed-effect modelling approach. The influence of demographic, anthropometric, treatment and comedication variables on the apparent clearance (CL/F) of VPA was studied. The bootstrap method was used to evaluate the final model internally. External evaluation was carried out using 776 VPA serum samples from 368 patients. (3) Results: A one-compartment model with first-order absorption and elimination successfully described the data. The final model included total body weight, age and comedication with phenytoin, phenobarbital and carbamazepine with a significant impact on VPA elimination. Internal and external evaluations demonstrated the good predictability of the model. (4) Conclusions: A PopPK model of VPA in Caucasian patients was successfully established, which will be helpful for model-informed precision dosing approaches in clinical patient care.

Effects of valproic acid on bone mineral density and bone metabolism: A meta-analysis

PURPOSE

Numerous studies have shown that the risk of fracture is increased by long-term antiepileptic drugs (AEDs). Valproic acid (VPA) is one of the most commonly used AEDs. In this meta-analysis, we aimed to assess the effects of VPA on bone mineral density (BMD) and bone metabolism.

METHODS

PubMed, Embase, Cochrane and Web of Science databases were searched from inception to January 2019 for articles focusing on the effects of VPA on BMD and bone metabolism in adults or children. A meta-analysis was performed using RevMan 5. 3 software.

RESULTS

18 studies were included in the meta-analysis. The BMD of lumber spine (MD= -0.06, 95%CI: -0.09 to -0.03, P < 0.0001) and femoral neck (MD= -0.05, 95% CI= -0.08 to -0.01, P = 0.02) was markedly decreased in the VPA group compared to healthy controls. Serum bone-specific alkaline phosphatase (BALP) level (SMD = 0.85, 95% CI: 0.30-1.40, P = 0.002) was notably increased in the VPA group compared to healthy groups. In the child group, the serum parathyroid hormone (PTH) level was higher than in healthy groups (SMD= -0.22, 95% CI: -0.40 to -0.04, P = 0.02); besides, the serum 25-hydroxy vitamin D3 (25(OH)D3) level was decreased (SMD= -0.22, 95% CI: -0.40 to -0.04, P = 0.02), while no significant alteration of these parameters was noted in the adult VPA group (P ≥ 0.05).

CONCLUSIONS

VPA may reduce the BMD of lumbar spine and femoral neck in patients with epilepsy while increasing the serum BALP level. Serum PTH level are increased and serum 25(OH)D3 level decreased in children with epilepsy treated with VPA. These parameters were unaltered in adults.

Effects of UGT2B7 Genetic Polymorphisms on Serum Concentrations of Valproic Acid in Chinese Children With Epilepsy Comedicated With Lamotrigine

BACKGROUND

Valproic acid (VPA) is widely used in the treatment of children with epilepsy. Genetic polymorphisms in genes encoding drug-metabolizing enzymes may be an important source of interindividual variability in VPA metabolism. VPA is a substrate of uridine diphosphate glucuronosyltransferase 2B7 (UGT2B7). In this study, we seek to evaluate the effects of genetic polymorphisms of the UGT2B7 gene on serum VPA concentrations in epileptic children comedicated with lamotrigine (LTG).

METHODS

We recruited 166 Chinese children with epilepsy who were treated with VPA in combination with LTG. Serum VPA and LTG concentrations were measured by fluorescence polarization immunoassay and high performance liquid chromatography, respectively. The UGT2B7 -161C > T in the 5'-upstream regions and 211 G > T, 372A > G, 735A > G, and 802C > T in the coding regions were genotyped using polymerase chain reaction amplification followed by direct automated DNA sequencing.

RESULTS

Our data show that patients carrying the variant UGT2B7 -161C > T or 802C > T genotypes had significantly higher adjusted VPA concentrations than those carrying the wild-type genotypes. The significant associations were potentiated after adjusted by age and adjusted LTG concentration. However, no associations were detected between the other studied UGT2B7 genotypes and adjusted VPA concentrations, even after adjusting by age and comedication.

CONCLUSIONS

These results suggest that the UGT2B7 -161C > T or 802C > T mutations affect VPA pharmacokinetics, which are potentially enhanced by age and concomitant LTG administration. These findings provide a potential mechanism underlying interindividual variation in the disposition of VPA in combination with LTG.

The pharmacogenomics of valproic acid

Valproic acid is an anticonvulsant and mood-stabilizing drug used primarily in the treatment of epilepsy and bipolar disorder. Adverse effects of valproic acid are rare, but hepatotoxicity is severe in particular in those younger than 2 years old and polytherapy. During valproic acid treatment, it is difficult for prescribers to predict its individual response. Recent advances in the field of pharmacogenomics have indicated variants of candidate genes that affect valproic acid efficacy and safety. In this review, a large number of candidate genes that influence valproic acid pharmacokinetics and pharmacodynamics are discussed, including metabolic enzymes, drug transporters, neurotransmitters and drug targets. Furthermore, pharmacogenomics is an important tool not only in further understanding of interindividual variability but also to assess the therapeutic potential of such variability in drug individualization and therapeutic optimization.

Analysis of the Variables Influencing Valproic Acid Concentration in the Serum and Cerebrospinal Fluid of Chinese Patients After Craniotomy

BACKGROUND

Valproic acid (VPA) has been widely used in Chinese patients after craniotomy. Many studies have focused on the influencing factors of VPA serum concentration, but conclusions are sometimes paradoxical. Furthermore, the concentration of VPA in the cerebrospinal fluid (CSF) has been rarely reported. In the present study, VPA CSF concentrations were measured, and the potential factors influencing serum concentration and CSF distribution of VPA were investigated. In addition, the functional relationship between serum and CSF concentration was explored.

METHODS

Subjects were patients who underwent craniotomy and were administrated with VPA and had a lumbar puncture. Serum and CSF VPA concentrations were measured by use of the Abbott i1000 system. CYP2C9 (430 C>T, 1075 A>C, 1076 T>C, 1080 C>G), UGT1A6 (541 A>G, 552 A>C), UGT2B7 (211 G>T, 802 C>T), and ABCB1 (1236 C>T, 2677 G>T/A, 3435 C>T) genotypes were determined by direct sequencing. Information, such as age, gender, and height, was collected, and their effect on serum and CSF VPA concentrations was investigated by univariate analysis and multiple linear regression analysis.

RESULTS

First, the concomitant use of carbapenems (β' = -0.422) and UGT1A6 (552 AA → AC) (β' = -0.249) had a significant negative correlation with the weight-adjusted VPA serum concentration (C:W ratio), whereas CYP2C9 (1075 AA → AC) (β' = 0.186) and gender (female compared with male) (β' = 0.322) showed a positive correlation with VPA serum C:W ratio. The coefficient of determination (R) was only 0.348. Second, the relationship between the serum concentration and the CSF square root of the concentration (R = 0.705) had a better linear fit. Third, serum VPA concentration (β' = 0.810), concomitant use of glycerol fructose (β' = 0.160), and age (≥65 compared with <65) (β' = 0.118) showed a positive correlation (R = 0.748) with the variability of square root of the concentration of the CSF.

CONCLUSIONS

In Chinese patients, after craniotomy, female patients with 1 or more of CYP2C9 (1075 AC) and UGT1A6 (552 AA) genotypes required a lower VPA dosage compared with male patient. There was a better-fitted linear relationship between VPA serum and the square root of CSF concentrations. CSF VPA concentrations were relatively stable, with only age and the use of glycerol fructose having a small influence.

Influence of age and co-medication on the steady-state pharmacokinetics of valproic acid in Tunisian patients with epilepsy

AIM

Valproic acid (VPA) is a widely prescribed broad-spectrum antiepileptic drug. However, the use of VPA is complicated in clinical practice by its remarkably wide variability of pharmacokinetics. The objective of this study was to investigate the effects of demographic factors and associated therapies on steady-state plasma VPA concentrations in patients with epilepsy.

METHODS

This retrospective cohort study was carried out using the routine therapeutic drug monitoring (TDM) database. Stepwise logistic regression analysis was used to compare serum VPA levels in 78 epilepsy patients treated with VPA in association with at least one other drug that could have interacted with CYP2C9, CYP2C19 or UGT enzymes.

RESULTS

The frequency of subtherapeutic serum VPA levels was significantly increased with younger age (P<0.02), the number of co-medications (P<0.007) and use of enzyme-inducing co-medications (P<0.02). No significant correlations between VPA dose and trough plasma concentrations were found, as the latter did not increase in proportion to the dose.

CONCLUSION

Routine monitoring of VPA serum levels would be extremely useful in epilepsy patients in the pediatric age group and in those who require associated enzyme-inducing medications.

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.

In Silico Modeling for the Prediction of Dose and Pathway-Related Adverse Effects in Humans From In Vitro Repeated-Dose Studies

Long-term repeated-dose toxicity is mainly assessed in animals despite poor concordance of animal data with human toxicity. Nowadays advanced human in vitro systems, eg, metabolically competent HepaRG cells, are used for toxicity screening. Extrapolation of in vitro toxicity to in vivo effects is possible by reverse dosimetry using pharmacokinetic modeling. We assessed long-term repeated-dose toxicity of bosentan and valproic acid (VPA) in HepaRG cells under serum-free conditions. Upon 28-day exposure, the EC50 values for bosentan and VPA decreased by 21- and 33-fold, respectively. Using EC(10) as lowest threshold of toxicity in vitro, we estimated the oral equivalent doses for both test compounds using a simplified pharmacokinetic model for the extrapolation of in vitro toxicity to in vivo effect. The model predicts that bosentan is safe at the considered dose under the assumed conditions upon 4 weeks exposure. For VPA, hepatotoxicity is predicted for 4% and 47% of the virtual population at the maximum recommended daily dose after 3 and 4 weeks of exposure, respectively. We also investigated the changes in the central carbon metabolism of HepaRG cells exposed to orally bioavailable concentrations of both drugs. These concentrations are below the 28-day EC(10) and induce significant changes especially in glucose metabolism and urea production. These metabolic changes may have a pronounced impact in susceptible patients such as those with compromised liver function and urea cycle deficiency leading to idiosyncratic toxicity. We show that the combination of modeling based on in vitro repeated-dose data and metabolic changes allows the prediction of human relevant in vivo toxicity with mechanistic insights.

Apparent clearance of valproic acid in elderly epileptic patients: estimation of the confounding effect of albumin concentration

BACKGROUND

Valproic acid (VPA) apparent clearance (CL) estimated from total serum concentrations is analogous in elderly and non-elderly adult patients. As drug-protein binding decreases in old age, the aim of our study was to evaluate the confounding effect of the serum albumin concentration on the VPA apparent CL in elderly patients.

METHODS

In 102 epileptic out-patients treated with VPA in monotherapy, serum total steady-state trough concentrations (Css) were determined. Css concentrations were normalized for a 42 g/L albumin concentration (Css(N)), and the apparent CL and normalized apparent CL(N) were calculated.

RESULTS

A poor concordance of 53% was found in the classification of Css and Css(N) levels of VPA as subtherapeutic, therapeutic, or supratherapeutic dose. In the elderly (≥65 years) and non-elderly adult patients, the VPA apparent CL was similar; however, normalized apparent CL(N) was significantly lower in older patients (P < 0.01), with a 40% median decrease.

CONCLUSIONS

Total VPA concentrations should be interpreted with caution, mainly in older patients, in which determination of unbound or normalized total drug concentrations may be clinically useful. Normalization of total concentrations permits an estimation of the masking effect of serum albumin concentrations on the VPA apparent CL in elderly patients.

Modern methods for analysis of antiepileptic drugs in the biological fluids for pharmacokinetics, bioequivalence and therapeutic drug monitoring

Epilepsy is a chronic disease occurring in approximately 1.0% of the world's population. About 30% of the epileptic patients treated with availably antiepileptic drugs (AEDs) continue to have seizures and are considered therapy-resistant or refractory patients. The ultimate goal for the use of AEDs is complete cessation of seizures without side effects. Because of a narrow therapeutic index of AEDs, a complete understanding of its clinical pharmacokinetics is essential for understanding of the pharmacodynamics of these drugs. These drug concentrations in biological fluids serve as surrogate markers and can be used to guide or target drug dosing. Because early studies demonstrated clinical and/or electroencephalographic correlations with serum concentrations of several AEDs, It has been almost 50 years since clinicians started using plasma concentrations of AEDs to optimize pharmacotherapy in patients with epilepsy. Therefore, validated analytical method for concentrations of AEDs in biological fluids is a necessity in order to explore pharmacokinetics, bioequivalence and TDM in various clinical situations. There are hundreds of published articles on the analysis of specific AEDs by a wide variety of analytical methods in biological samples have appears over the past decade. This review intends to provide an updated, concise overview on the modern method development for monitoring AEDs for pharmacokinetic studies, bioequivalence and therapeutic drug monitoring.

[Therapeutic drug monitoring of valproate]

Valproic acid is an anticonvulsant drug available in France since 1967. It is a broad spectrum molecule indicated in various forms of epilepsy of the adult and the child, but it is also prescribed in the treatment of different other pathologies of nervous system. The divalproate sodium is indicated in the treatment of bipolar disorders. The valproic acid is marketed under various pharmaceutical forms, with different corresponding tmax values. But, whatever the administered preparation, the circulating active molecule is the ion valproate. Elimination half-life is from 11 to 20 h. Metabolization of valproate is important and represents its main route of elimination. Valpromide is comparable to a prodrug which metabolizes in valproate. The inter and intraindividual variability of the plasma concentrations are important. Several studies show a concentration-effect relationship, but two interventional trials ended in the lack of interest of the Therapeutic Drug Monitoring (TDM), although it is of current practice. However, numerous drug interactions may modify the plasma concentrations of valproate. The therapeutic range is from 50 to 100 mg/L (346-693 micromol/L). The level of proof of the interest of the TDM for this molecule was estimated in: recommended.

Effect of aging on glucuronidation of valproic acid in human liver microsomes and the role of UDP-glucuronosyltransferase UGT1A4, UGT1A8, and UGT1A10

Valproic acid (VPA) is a widely used anticonvulsant that is also approved for mood disorders, bipolar depression, and migraine. In vivo, valproate is metabolized oxidatively by cytochromes P450 and beta-oxidation, as well as conjugatively via glucuronidation. The acyl glucuronide conjugate (valproate-glucuronide or VPAG) is the major urinary metabolite (30-50% of the dose). It has been hypothesized that glucuronidation of antiepileptic drugs is spared over age, despite a known decrease in liver mass. The formation rates of VPAG in a bank of elderly (65 years onward) human liver microsomes (HLMs) were measured by liquid chromatography/tandem mass spectrometry and compared with those in a younger (2-56 years) HLM bank. In vitro kinetic studies with recombinant UDP-glucuronosyltransferases (UGTs) were completed. A 5- to 8-fold variation for the formation of VPAG was observed within the microsomal bank obtained from elderly and younger donors. VPAG formation ranged from 6.0 to 53.4 nmol/min/mg protein at 1 mM substrate concentration (n=36). The average velocities at 0.25, 0.5, and 1 mM VPA were 7.0, 13.4, and 25.4 nmol/min/mg protein, respectively, in the elderly HLM bank. Rates of VPAG formation were not significantly different in the HLM bank obtained from younger subjects. Intrinsic clearances (V(max)/K(m)) for several cloned, expressed UGTs were determined. UGT1A4, UGT1A8, and UGT1A10 also were found to catalyze the formation of VPAG in vitro. This is the first reported activity of these UGTs toward VPA glucuronidation. UGT2B7 had the highest intrinsic clearance, whereas UGT1A1 demonstrated no activity. In conclusion, our investigation revealed no differences in VPAG formation in younger versus elderly HMLs and revealed three other UGTs that form VPAG in vitro.

Population Pharmacokinetics of Valproic Acid Concentrations in Elderly Nursing Home Residents

The objective of this study was to identify factors that affect valproic acid (VPA) apparent clearance (CL/F) in elderly nursing home residents. Inclusion criteria included residency in a nursing home for at least 2 months, aged 65 years or older, a stable dosing regimen of VPA for at least 4 weeks, VPA concentration, and complete dosing information. CL/F was analyzed by a nonlinear mixed effects model. A one-compartment model with first-order absorption and elimination was used. Both volume and absorption rate constant were fixed (14 L and 1 hr, respectively). Covariates were tested by forward inclusion and backward elimination. Interindividual variability in clearance was estimated using an exponential error model and expressed as a coefficient of variation. Residual error was estimated using a combined additive and constant coefficient of variation error model. The study consisted of 405 observations from 146 (52 men, 94 women) elderly nursing home residents. CL/F was not affected by age or weight. The population CL/F was 0.843 L/hr. CL/F was 1) 27% lower in female residents; 2) 41% greater when the resident was on concomitant metabolic inducers carbamazepine or phenytoin cotherapy; and 3) 25% greater when the syrup formulation was used. Variability in CL/F was 32.9%. Coefficient of variation and standard deviation of the residual error were 18.2% and 10.6 mg/L, respectively. The increased CL/F in patients taking VPA syrup may be the result of a decreased bioavailability (F) rather than an increased CL that could be associated with pathology requiring use of the syrup rather than an inherent property of the drug formulation. The results from this study may be useful for individualizing dose regimens in the nursing home population based on patient-specific factors.