Free Valproic Acid Research Articles

Valproate serum concentrations in patients with hypoalbuminemia and medical complications.

Valproic acid (VPA) and its derivatives are highly protein bound with free fraction increasing with dose and serum concentration. Consensus guidelines regarding dose adjustment for hypoalbuminemia are not available. A literature search was performed using PubMed to identify articles with the following key terms: "valproate," "valproic acid," "protein binding," "albumin," and "hypoalbuminemia." We report our findings as well as 5 cases involving pharmacokinetic impact of hypoalbuminemia on valproate. A previously published model for normalizing VPA serum concentration for hypoalbuminemia in patients with epilepsy was compared to results for 5 cases (4 female, 1 male) in which VPA was used for psychiatric illness. Only 1 of the cases had free serum concentrations in the range that would be expected with the model. Free concentrations ranged from 22% to 83% with no clear relationship to other factors (weight, age, serum creatinine, or dose). Female patients with similar albumin had higher free fractions than the 1 male patient. Due to the variability in pharmacokinetic impact of hypoalbuminemia, it is important to monitor patients closely for signs of VPA toxicity in cases involving altered albumin levels. It would be prudent to use free serum VPA concentrations when patients experience fluctuations in albumin or have unexpected response to medication.

The Influence of Plasma Albumin Concentration on the Analysis Methodology of Free Valproic Acid by Ultrafiltration and Its Application to Therapeutic Drug Monitoring.

Free drug analysis is increasingly becoming popular in therapeutic drug monitoring (TDM). Centrifugal ultrafiltration (CF-UF) is the primary method to separate free drug from that of bound drug. However, the volume ratio of ultrafiltrate to sample solution (Vu/Vs) affects the accuracy of CF-UF, which highly depends on the different plasma conditions. Plasma protein concentrations in patients are different from those observed in healthy subjects, and there are also significant differences among patients with different diseases. Only very few studies have reported on the effect of protein concentration on the analysis methodology of free drug by CF-UF. In this study, valproic acid was used as the representative drug, and plasma samples with different albumin concentrations were analyzed by CF-UF and hollow fiber centrifugal ultrafiltration (HFCF-UF). There was no significant difference of free drug concentrations by HFCF-UF and CF-UF when plasma albumin concentrations ranged 40-60 g/L. However, at low albumin concentrations (<40 g/L), a considerable difference was detected, and the difference was increased with the decrease of plasma albumin concentration. When the albumin concentration was as low as 10 g/L, the free drug concentration was 17.3 mcg/mL by CF-UF, whereas it was 10.2 mcg/mL by HFCF-UF. The accuracy of free drug measurement by CF-UF was albumin concentration dependent. However, such an effect was not observed when samples were prepared by HFCF-UF, which was more suitable for TDM of plasma samples from different patients. Therefore, this method could be readily applied to the measurement of free valproic acid plasma concentrations for TDM in patients.

New insights into the molecular and epigenetic effects of antitumor Pt(IV)-valproic acid conjugates in human ovarian cancer cells

Substitutionally inert Pt(IV) prodrugs, combining bioactive axial ligands with Pt(IV) derivatives of antitumor Pt(II) compounds, represent a new generation of anticancer drugs. The rationale behind these prodrugs is to release, by reductive elimination inside the cancer cell, an active Pt(II) drug which binds nuclear DNA as well as bioactive ligands that may potentiate toxic effects of the Pt(II) drugs by an independent pathway. Platinum prodrugs, such as Pt(IV) derivatives of cisplatin containing axial valproic acid (VPA) ligands, destroy cancer cells with greater efficacy than conventional cisplatin. These axial ligands were chosen because VPA inhibits histone deacetylase (HDAC) activity, thereby decondensing chromatin and subsequently increasing the accessibility of DNA within chromatin to DNA-binding agents. We examined the mechanism of cytotoxic activity of Pt(IV) derivatives of cisplatin with VPA axial ligands. Particular attention was paid to the role of the VPA ligand in these Pt(IV) prodrugs in the mechanism underlying their toxic effects in human ovarian tumor cells. We demonstrate that (i) treatment of the cells with these prodrugs resulted in enhanced histone H3 acetylation and decondensation of heterochromatin markedly more effectively than free VPA; (ii) of the total Pt inside the cells, a considerably higher fraction of Pt from the Pt(IV)-VPA conjugates is bound to DNA than from the conjugates with biologically inactive ligands. The results indicate that the enhanced cytotoxicity of the Pt(IV)-VPA conjugates is a consequence of several processes involving enhanced cellular accumulation, downregulation of HDACs and yet other biochemical processes (not involving HDACs) which may potentiate antitumor effects.

Syntheses of valpromide dipeptide derivatives and interactions of derivatives with ctDNA

Two types of valproamide dipeptides, i.e., valproic acid (VPA)-Tyr-Tyr and VPA-His-His, were synthesized via Fmoc solid-phase peptide synthesis, purified via reversed-phase HPLC, and characterized via 1H, 13C NMR and ESI–MS to promote the interaction of valproic acid derivative with biological molecular. The interactions of VPA-Tyr-Tyr and VPA-His-His with DNA were investigated via UV–Vis absorption spectroscopy, fluorescence spectroscopy, and gel electrophoresis. The results showed that both VPA-Tyr-Tyr and VPA-His-His interacted with ctDNA through the groove binding mode and exhibited higher affinity for ctDNA compared with free VPA. Therefore, the valpromide derivatives modified by dipeptides have significant practical value in future studies.

N-valproyl-L-phenylalanine as new potential antiepileptic drug: synthesis, characterization and in vitro studies on stability, toxicity and anticonvulsant efficacy.

Valproic acid (VPA) is considered first-line drug in treatment of generalized idiopathic seizures such as absence, generalized tonic-clonic and myoclonic seizures. Among major antiepileptic drugs, VPA is also considered effective in childhood epilepsies and infantile spasms. Due to its broad activity, VPA acts as a mood stabilizer in bipolar disorder and it is useful in migraine prophylaxis. Despite its long-standing usage, severe reactions to VPA, such as liver toxicity and teratogenicity, are reported. To circumvent side effects due to structural characteristics of VPA, we synthesized in good yield a new VPA-aminoacid conjugate, the N-valproyl-L-Phenylalanine, and characterized by FT-IR, MS, (13)C and (1)H- NMR analyses. The Log D(pH7.4) value (0.19) indicated that new molecule was potentially able to cross biological membranes. The resistance to chemical and enzymatic hydrolysis of N-valproyl-L-phenylalanine was also assessed. All trials suggested that the compound, at the pH conditions of the entire gastro-intestinal tract, remained unmodified. Furthermore, the new compound did not undergo enzymatic cleavage both in plasma and in cerebral medium up to 24 h. The toxicity assay on primary cultures of astrocytes indicated that the synthetized conjugate was less toxic than both free VPA and L-Phenylalanine. In this paper, the anticonvulsant activity of the new compound against epileptic burst discharges evoked in vitro in rat hippocampal slices was also evaluated. These preliminary results underline that N-valproyl-L-phenylalanine as new potential antiepileptic agent could represent a good candidate to further investigations.

Correlation of saliva and serum free valproic acid concentrations in persons with epilepsy

PurposeTherapeutic drug monitoring (TDM) of antiepileptic drugs (AEDs) in serum is frequently used in clinical settings however saliva could be an alternative to measure free concentration of drugs. In the present study, we observed the possible correlation of VPA concentration between serum and saliva in persons with epilepsy (PWE). MethodsA total of 59 paired serum and saliva samples were assayed from 65 consecutive PWE (51 males and 14 females; age range 9–65 years). Patients were subjected to either VPA monotherapy or its combination with other AEDs for at least three months. Steady state trough concentration of unbound VPA drug was quantified using HPLC. The correlation between serum and saliva free VPA concentration was evaluated. ResultsOut of 65 patients, 27 were on monotherapy of VPA and 38 were on VPA with other antiepileptic drugs. Saliva VPA concentration significantly correlated with serum free VPA concentration (p<0.05). Poor correlation was observed between serum and saliva VPA concentration with the daily dose (p>0.05) respectively. ConclusionsOur study reveals that serum and saliva VPA concentrations are significantly associated in PWE. These associations may facilitate monitoring and evaluation of VPA levels non-invasively for PWE.

From the covalent linkage of drugs to novel inhibitors of ribonucleotide reductase: Synthesis and biological evaluation of valproic esters of 3′-C-methyladenosine

We synthesized a series of serum-stable covalently linked drugs derived from 3′-C-methyladenosine (3′-Me-Ado) and valproic acid (VPA), which are ribonucleotide reductase (RR) and histone deacetylase (HDAC) inhibitors, respectively. While the combination of free VPA and 3′-Me-Ado resulted in a clear synergistic apoptotic effect, the conjugates had lost their HDAC inhibitory effect as well as the corresponding apoptotic activity. Two of the analogs, 2′,5′-bis-O-valproyl-3′-C-methyladenosine (A160) and 5′-O-valproyl-3′-C-methyladenosine (A167), showed promising cytotoxic activities against human hematological and solid cancer cell lines. A167 was less potent than A160 but had interesting features as an RR inhibitor. It inhibited RR activity by competing with ATP as an allosteric effector and concomitantly reduced the intracellular deoxyribonucleoside triphosphate (dNTP) pools. A167 represents a novel lead compound, which in contrast to previously used RR nucleoside analogs does not require intracellular kinases for its activity and therefore holds promise against drug resistant tumors with downregulated nucleoside kinases.

Dendrimer Brain Uptake and Targeted Therapy for Brain Injury in a Large Animal Model of Hypothermic Circulatory Arrest

Treatment of brain injury following circulatory arrest is a challenging health issue with no viable therapeutic options. Based on studies in a clinically relevant large animal (canine) model of hypothermic circulatory arrest (HCA)-induced brain injury, neuroinflammation and excitotoxicity have been identified as key players in mediating the brain injury after HCA. Therapy with large doses of valproic acid (VPA) showed some neuroprotection but was associated with adverse side effects. For the first time in a large animal model, we explored whether systemically administered polyamidoamine (PAMAM) dendrimers could be effective in reaching target cells in the brain and deliver therapeutics. We showed that, upon systemic administration, hydroxyl-terminated PAMAM dendrimers are taken up in the brain of injured animals and selectively localize in the injured neurons and microglia in the brain. The biodistribution in other major organs was similar to that seen in small animal models. We studied systemic dendrimer–drug combination therapy with two clinically approved drugs, N-acetyl cysteine (NAC) (attenuating neuroinflammation) and valproic acid (attenuating excitotoxicity), building on positive outcomes in a rabbit model of perinatal brain injury. We prepared and characterized dendrimer-NAC (D-NAC) and dendrimer-VPA (D-VPA) conjugates in multigram quantities. A glutathione-sensitive linker to enable for fast intracellular release. In preliminary efficacy studies, combination therapy with D-NAC and D-VPA showed promise in this large animal model, producing 24 h neurological deficit score improvements comparable to high dose combination therapy with VPA and NAC, or free VPA, but at one-tenth the dose, while significantly reducing the adverse side effects. Since adverse side effects of drugs are exaggerated in HCA, the reduced side effects with dendrimer conjugates and suggestions of neuroprotection offer promise for these nanoscale drug delivery systems.

Effect of short course, high-dose valproic acid on proliferation in breast adenocarcinomas.

e13522 Background: Our in vitro and in vivo studies showed that single agent valproic acid (VPA), a histone deacetylase (HDAC) inhibitor, is effective in a subset of breast cancers. Whether VPA is effective as a single agent and what the optimal dosing would be are unknown. Methods: In an ongoing IRB-approved, window-of-opportunity study testing a genomic predictor of sensitivity to VPA (NCT01007695), we performed biopsies and DCE-MRI on women before and after seven days of escalating doses of VPA on untreated women with breast adenocarcinoma with an intact breast tumor. Within patient dose-escalation was done with a goal dose of 50 mg/kg. Proliferation was assessed with MIB-1 immunohistochemistry. Only correlative secondary endpoints are presented here. Results: Sixteen women have completed treatment and are evaluable. Total and free VPA levels on the last day of treatment averaged 136 µg/ml (range 15-242) and 30 µg/ml (range 1-90), respectively. Proliferation rate by MIB-1 decreased by and average of -7.25% (range +4% to -45%, p=0.04). The change in proliferation did not correlated with VPA levels, although only one of four women with VPA levels less than 100 µg/ml had a decrease in proliferation, compared to five of twelve women with VPA levels greater than 100 µg/ml. Four women had MIB-1 decreases of 10% or greater. Two women have had post-treatment biopsies with fibrosis similar to that seen with chemotherapy treatment effect. DCE-MRI parameters, including ktrans, vp, and kep, did not change significantly with VPA treatment or correlate with VPA levels. Conclusions: VPA as a single agent can reduce proliferation in a subset of women with breast cancers. Higher VPA levels are needed than those achieved at standard dose levels, but VPA levels by themselves do not predict effect. Other monitoring parameters, such as peripheral blood histone acetylation changes, or other predictors of benefit are needed. Clinical trial information: NCT01007695.

Determination of free and total valproic acid in human plasma by capillary electrophoresis with contactless conductivity detection

A new approach for the determination of free and total valproic acid in small samples of 140μL human plasma based on capillary electrophoresis with contactless conductivity detection is proposed. A dispersive liquid–liquid microextraction technique was employed in order to remove biological matrices prior to instrumental analysis. The free valproic acid was determined by isolating free valproic acid from protein-bound valproic acid by ultrafiltration under centrifugation of 100μL sample. The filtrate was acidified to turn valproic acid into its protonated neutral form and then extracted. The determination of total valproic acid was carried out by acidifying 40μL untreated plasma to release the protein-bound valproic acid prior to extraction. A solution consisting of 10mM histidine, 10mM 3-(N-morpholino)propanesulfonic acid and 10μM hexadecyltrimethylammonium bromide of pH 6.5 was used as background electrolyte for the electrophoretic separation. The method showed good linearity in the range of 0.4–300μg/mL with a correlation coefficient of 0.9996. The limit of detection was 0.08μg/mL, and the reproducibility of the peak area was excellent (RSD=0.7–3.5%, n=3, for the concentration range from 1 to 150μg/mL). The results for the free and total valproic acid concentration in human plasma were found to be comparable to those obtained with a standard immunoassay. The corresponding correlation coefficients were 0.9847 for free and 0.9521 for total valproic acid.

DETERMINATION OF TOTAL AND UNBOUND CONCENTRATIONS OF VALPROIC ACID IN HUMAN PLASMA BY LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY

An analytical method for the determination of valproic acid in human plasma and ultrafiltrated human plasma has been developed and validated. The analytical method lies in the solid phase extraction of valproic acid (VPA), followed by its quantification through an LC-MS method, using benzoic acid as the internal standard. The intra-assay and inter-assay precisions of this technique ranged between 4.29% and 9.91% and its accuracy ranged between 1.00% and 7.73%, for VPA spiked in plasma matrix. For VPA spiked in ultrafiltrated plasma, matrix precisions were from 6.29% to 9.84% and accuracies, from −1.17% to 5.38%. The limit of quantification was set at 1 µg/mL (precision 3.20%, accuracy 11.31%). The linear working range of concentrations was established between 10 and 250 µg/mL for the plasma matrix and between 1 and 100 µg/mL for the ultrafiltrated plasma matrix. The absolute recovery of valproic acid was over 82% in the studied range of concentrations in both matrixes. Valproic acid was found to be stable in both matrixes at the assayed conditions. This method has shown to be suitable for the analysis of free and total valproic acid concentrations in human plasma samples.

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.

The Diurnal Fluctuations in Free and Total Serum Valproic Acid Concentration at Steady State in Epileptic Children

The Diurnal Fluctuations in Free and Total Serum Valproic Acid Concentration at Steady State in Epileptic Children

High Unbound Fraction of Valproic Acid in a Hypoalbuminemic Critically III Patient on Renal Replacement Therapy

Objective: To describe a hypoalbuminemic critically ill patient with subtherapeutic total valproic acid serum concentrations but unbound valproic acid concentrations within normal limits. Case Summary: During an intensive care unit admission, a 61-year-old woman with urosepsis and multiorgan dysfunction syndrome developed tonic-clonic seizures with respiratory failure, and tracheal intubation was performed. An intravenous loading dose of valproic acid 1500 mg (25 mg/kg) was administered and therapy was continued with valproic acid 750 mg (12.5 mg/kg) twice daily. Because of progressive renal failure, continuous venovenous hemofiltration was started on day 3 of valproic acid therapy. On day 7 of valproic acid therapy, routine testing of serum valproic acid trough concentration returned as undetectable. Subsequent determinations of trough serum concentrations of total valproic acid showed values below the therapeutic range. Data from a full pharmacokinetic curve (multiple blood samples during a dosing interval) showed that the free fraction of valproic acid was &gt;60%. Although total valproic acid concentrations were still low, the unbound concentrations were considered therapeutic. Serum albumin was 1.2 g/dL on the multiple sampling day, Discussion: The patient's hypoalbuminemia probably explains the remarkably high free fraction of valproic acid. Our hypothesis is that the low albumin level was associated with high plasma clearance of valproic acid, leading to extremely low total drug concentrations. To our knowledge, this high percentage of free valproic acid has not been previously described. Conclusions: Healthcare professionals should be aware of the need of early determination of both total and free fraction valproic acid serum concentrations in hypoalbuminemic critically ill patients. Increasing the dose of valproic acid purely based on total valproic acid serum concentrations in this patient population should be avoided.

High Unbound Fraction of Valproic Acid in a Hypoalbuminemic Critically Ill Patient on Renal Replacement Therapy

To describe a hypoalbuminemic critically ill patient with subtherapeutic total valproic acid serum concentrations but unbound valproic acid concentrations within normal limits. During an intensive care unit admission, a 61-year-old woman with urosepsis and multiorgan dysfunction syndrome developed tonic-clonic seizures with respiratory failure, and tracheal intubation was performed. An intravenous loading dose of valproic acid 1500 mg (25 mg/kg) was administered and therapy was continued with valproic acid 750 mg (12.5 mg/kg) twice daily. Because of progressive renal failure, continuous venovenous hemofiltration was started on day 3 of valproic acid therapy. On day 7 of valproic acid therapy, routine testing of serum valproic acid trough concentration returned as undetectable. Subsequent determinations of trough serum concentrations of total valproic acid showed values below the therapeutic range. Data from a full pharmacokinetic curve (multiple blood samples during a dosing interval) showed that the free fraction of valproic acid was >60%. Although total valproic acid concentrations were still low, the unbound concentrations were considered therapeutic. Serum albumin was 1.2 g/dL on the multiple sampling day. The patient's hypoalbuminemia probably explains the remarkably high free fraction of valproic acid. Our hypothesis is that the low albumin level was associated with high plasma clearance of valproic acid, leading to extremely low total drug concentrations. To our knowledge, this high percentage of free valproic acid has not been previously described. Health-care professionals should be aware of the need of early determination of both total and free fraction valproic acid serum concentrations in hypoalbuminemic critically ill patients. Increasing the dose of valproic acid purely based on total valproic acid serum concentrations in this patient population should be avoided.

The Impact of Dosage of Sustained-Release Formulation on Valproate Clearance and Plasma Concentration in Psychiatric Patients

Pharmacokinetic parameters were compared between 2 dosages of valproic acid (VPA) sustained-release (SR) formulation in psychiatric patients. A total of 66 psychiatric patients (21 women and 45 men; age range, 18-60 years) receiving 500 mg/d (n = 28) or 1000 mg/d (n = 38) of VPA SR for at least 4 weeks were recruited into the study. A 5-mL blood sample was collected into a plain tube and immediately centrifuged for plasma. Separation of free VPA was further done using Centrifree micropartition devices. Both total and free VPA concentrations (C(total) and C(free)) were analyzed by TDx analyzer with fluorescence polarization immunoassay technique. The patients' characteristics and pharmacokinetic parameters were compared between the 2 dosage groups using independent t test or χ² test where appropriate. The results show that the increment in C(total) (mg/mL) for every milligram-per-kilogram increment in dosage was decreased from 7 ± 3 to 4 ± 1 (mg/L) / (mg/kg) when the total VPA clearance (CL(total)) increased from 6.1 ± 2.6 to 9.0 ± 3.1 mL/kg per hour with the increasing dose in the 500 mg/d and 1000 mg/d groups, respectively (P < 0.05). The increment in C(free) [0.6 ± 0.3 vs 0.5 ± 0.2 (mg/L) / (mg/kg)] and CL(free) (80.4 ± 41.5 vs 92.2 ± 47.6 ml/kg per hour) were not significantly different. Owing to the saturation of protein binding, percent free VPA was significantly increased from 8 ± 3 to 11 ± 3 when the dose was increased from 500 to 1000 mg/d (P < 0.05). In conclusion, an increase in the VPA dose resulted in a disproportional increase between dosage and C(total), whereas a proportional increase between dosage and C(free) still existed. Therefore, our study suggests that the therapeutic range of C(free) is 4 to 12 mg/L based on the therapeutic range of C(total) (45-100 mg/L) for general psychiatric conditions.

Phase 1 Study of Valproic Acid in Pediatric Patients with Refractory Solid or CNS Tumors: A Children's Oncology Group Report

The primary purpose of this trial was to define and describe the toxicities of oral valproic acid (VPA) at doses required to maintain trough concentrations of 100 to 150 mcg/mL or 150 to 200 mcg/mL in children with refractory solid or central nervous system (CNS) tumors. Secondary objectives included assessment of free and total VPA pharmacokinetics (PKs) and histone acetylation in peripheral blood mononuclear cells (PBMC) at steady state. Oral VPA, initially administered twice daily and subsequently three times daily, was continued without interruption to maintain trough concentrations of 100 to 150 mcg/mL. First-dose and steady-state PKs were studied. Histone H3 and H4 acetylation in PBMCs was evaluated using an ELISA technique. Twenty-six children, sixteen of whom were evaluable for toxicity, were enrolled. Dose-limiting somnolence and intratumoral hemorrhage were associated with VPA troughs of 100 to 150 mcg/mL. Therefore, the final cohort of six children received VPA to maintain troughs of 75 to 100 mcg/mL and did not experience any dose-limiting toxicity. First-dose and steady-state VPA PK parameters were similar to values previously reported in children with seizures. Increased PBMC histone acetylation was documented in 50% of patients studied. One confirmed partial response (glioblastoma multiforme) and one minor response (brainstem glioma) were observed. VPA administered three times daily to maintain trough concentrations of 75 to 100 mcg/mL was well tolerated in children with refractory solid or CNS tumors. Histone hyperacetylation in PBMCs was observed in half of the patients at steady state. Future trials combining VPA with chemotherapy and/or radiation therapy should be considered, especially for CNS tumors.

The relationship between glucuronide conjugate levels and hepatotoxicity after oral administration of valproic acid

The aim of this study was to investigate the relationship between hepatotoxicity, levels of glucuronide conjugates of valproic acid (VPA), and the toxic metabolites of VPA (4-ene VPA and 2,4-diene VPA). We also examined whether hepatotoxicity could be predicted by the urinary excretion levels of VPA and its toxic metabolites. VPA was administrated orally in rats in amounts ranging from 20 mg/kg to 500 mg/kg. Free and total (free plus glucuronide conjugated) VPA, 4-ene VPA, and 2,4-diene VPA were quantified in urine and liver using gas chromatography-mass spectrometry. Serum levels of aspartate aminotransferase, alanine aminotransferase, and alpha-glutathione S-transferase (alpha-GST) were also determined to measure the level of hepatotoxicity. The serum alpha-GST level increased slightly at the 20 mg/kg dose, and substantially increased at the 100 and 500 mg/kg dose; aspartate aminotransferase and alanine aminotransferase levels did not change with the administration of increasing doses of VPA. The liver concentration of free 4-ene VPA and the urinary excretion of total 4-ene VPA were the only measures that correlated with the increase in the serum alpha-GST level (p < 0.094 and p < 0.023 respectively). From these results, we conclude that hepatotoxicity of VPA correlates with liver concentration of 4-ene VPA and can be predicted by the urinary excretion of total 4-ene VPA.

Hyperammonemia and Valproic Acid-Induced Encephalopathy

Back to table of contents Previous article Next article Letters to the EditorFull AccessHyperammonemia and Valproic Acid-Induced EncephalopathyBOBECK MODJTAHEDI B.S.GLEN L. XIONG M.D.,BOBECK MODJTAHEDI B.S.Search for more papers by this authorGLEN L. XIONG M.D.Search for more papers by this author,Published Online:1 Dec 2007https://doi.org/10.1176/appi.ajp.2007.07081270AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail To The Editor: We read with great interest the thought-provoking clinical case conference by Russell B. Carr, M.D., and Kerrie Shrewsbury, M.D., in the July 2007 issue of the Journal describing the difficulty in predicting hyperammonemia-induced encephalopathy. The authors stated that “hyperammonemia occurs at both therapeutic and supratherapeutic concentrations of valproic acid, implying that other factors often influence the development of symptomatic hyperammonemia” ( 1 , p. 1022). We propose that increased free valproic acid levels in the presence of normal total levels might be an unidentified factor that may mediate hyperammonemia as well as valproic acid-induced encephalopathy. The importance of monitoring free valproic acid levels has been described in several single-case and case-series reports and deserves more systematic research. A high free valproic acid level with a normal total valproic acid level has been described when both valproic acid and aspirin were taken (2) . The relationship between free and total valproic acid was shown to be linear when the total valproic acid level was in the lower therapeutic range (r=0.68) (3) . However, free fraction of valproic acid increases nonlinearly at higher total valproic acid levels. Similarly, Henriksen et al. (4) found nonlinear increases of free valproic acid above the recommended therapeutic total valproic acid range when protein binding sites were saturated. Using available data from Buchanan and Ponniah (5) , Figure 1 demonstrates an exponential increase in free valproic acid with increased concentration of total valproic acid (7.4×e 0.0035 , R 2 =0.93). This exponential relationship shows a stronger fit than the linear relationship noted by Roman et al. (3) (r=0.68 vs. R 2 =0.93). Figure 1. Relationship Between Free Valproic Acid and Total Valproic Acid aa Data from Buchanan N and Ponniah P (5). Upon valproic acid binding site saturation on albumin, subsequent incremental changes in total valproic acid may cause disproportional increases in free valproic acid. This may play a significant role in adverse effects, particularly when other drugs that might inhibit valproic acid metabolism are also administered (2) . We agree with Drs. Carr and Shrewsbury that polypharmacy and malnutrition are among the most likely risk factors for hyperammonemia. Under these circumstances, pharmacologically significant drug-drug interactions should be a cause of considerable concern. To better understand the relationship between valproic acid and hyperammonemia, it appears prudent to monitor free valproic acid levels, especially in the setting of polypharmacy and hypoalbuminemia. Sacramento, Calif.The authors report no competing interests.This letter (doi: 10.1176/appi.ajp.2007.07081270) was accepted for publication in September 2007.

Plasma and cerebrospinal fluid pharmacokinetics of valproic acid after oral administration in non-human primates

Valproic acid (VPA), a widely used antiepileptic, also inhibits histone deacetylase (HDAC), and is undergoing evaluation as an anti-cancer agent. We studied the pharmacokinetics of VPA in the plasma and cerebrospinal fluid (CSF) in a non-human primate model that is highly predictive of human CSF penetration to determine if levels of VPA required to inhibit HDAC in in vivo models can be attained. Oral VPA, 75 mg/kg, was administered to four non-human primates. Serial samples of blood (n = 4) and CSF (n = 3) were obtained for pharmacokinetic studies of total and free VPA. Plasma and CSF VPA concentrations were measured using the commercially available Abbott AxSYM VPA assay reagent system (Abbott Laboratories, Abbott Park, IL, USA). The resultant plasma and CSF data were evaluated using pharmacokinetic modeling methods. At a dose of 75 mg/kg, the maximum plasma concentration of VPA was 130.1 +/- 70.6 microg/ml (mean +/- standard deviation) for total drug and 53.3 +/- 44.4 microg/ml for free drug. The mean plasma area under the curve (AUC) for total drug was 680 +/- 233 microg/ml h and for free drug 146 +/- 89 microg/ml hr. The maximum CSF concentration occurred 2-3 h after administration and was 28.2 +/- 18.6 microg/ml. The CSF AUC for VPA was 108 +/- 52 microg/ml h. The CSF penetration of VPA was 12.9 +/- 5.1% for total drug and 57.0 +/- 8.7% for free drug. Disappearance from the plasma followed non-linear kinetics with a V (max) of 321.2 +/- 65.6 microg/kg/min and a K (m) of 17.2 +/- 13.7 mg/l. Valproic acid deserves further study for the treatment of CNS tumors given its high CSF penetration after oral dosing coupled with the anti-tumor activity observed in preclinical studies.