Pharmacokinetics of valproic acid in patients with bipolar disorder

Predictive ability of published population pharmacokinetic models of valproic acid in Thai manic patients

WHAT IS KNOWN AND OBJECTIVE

Population pharmacokinetic (PopPK) models of valproic acid (VPA) have been developed to aid individualized drug dosing, but most of these have been based on the treatment of epileptic patients and recent evidence shows that VPA clearance (CL_VPA ) in manic patients differs from that in epileptic patients. In the light of this, the predictive ability of selected VPA PopPK models based on epileptic patients was assessed to determine whether they could be used with patients with mania.

METHODS

VPA PopPK models that were based on the treatment of epileptic patients and developed using a non-linear mixed-effect approach with a one-compartment structure were selected and used to predict the VPA concentrations of a validation data set. The mean absolute prediction error (MAPE) and root mean square error (RMSE) were used to assess the accuracy and precision of the model.

RESULTS

The validation data set consisted of 235 Thai manic patients with a mean age of 39.6 years and a mean weight of 62.8 kg. Five models were selected to predict VPA concentrations in patients suffering from mania, and these were labelled A, C, E, F and G. The results showed that all models sufficiently predicted VPA concentrations in patients with mania, and of the models studied, G provided the most accurate and precise predictions, with MAPE and RMSE of 23% and 29.75, respectively.

WHAT IS NEW AND CONCLUSION

VPA PopPK models developed using patients with epilepsy can also be used for individualized dosing of patients with mania, but before implementation, the accuracy of these models' predictions should be assessed in the target population.

The Risk of Thrombocytopenia During Valproic Acid Therapy: A Critical Summary of Available Clinical Data

Valproate is an effective anti-epileptic and mood stabilizer drug, but its prescription may be complicated by the development of thrombocytopenia. The purpose of the present manuscript is to provide a critical overview about the risk of thrombocytopenia during treatment with valproate. A search of the main database sources has been conducted to identify relevant papers about the topic. In the studies with a larger sample size (> 150 subjects), thrombocytopenia occurred in 12–18% of subjects receiving treatment with valproate. Advanced age, female gender, and high doses were found to be risk factors for the development of thrombocytopenia during treatment with valproate. Future research is needed to clarify the clinical impact of the occurrence of thrombocytopenia during valproate treatment (e.g., the risk of life-threatening events such as stroke or the development of thrombocytopenia during short- versus long-term administration, or oral versus intravenous formulations).

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.

Interaction of valproic acid and amitriptyline: analysis of therapeutic drug monitoring data under naturalistic conditions

Amitriptyline (AMI) and valproic acid (VPA) are common psychotropic drugs which are frequently used in psychiatry and also administered in neurology or anesthesia in the absence of a psychiatric indication. On the basis of the case of a 73-year-old man with therapy-resistant major depressive episode who experienced anticholinergic delirium after adding VPA to AMI, we retrospectively analyzed therapeutic drug monitoring data of the years 2008 to 2010. We assessed cases receiving a combination of AMI and VPA, and obtained a control sample of AMI patients without VPA which were matched for sex, age, daily dose, and comedication. Both samples were compared regarding the serum levels of AMI and nortriptyline (NOR) as well as the ratio of NOR and AMI with the Mann-Whitney U test. The combination of AMI and VPA led to a remarkable increase of AMI and NOR serum levels. When comparing 33 patients who received comedication with VPA versus 33 matched controls, the total concentration by combining mean AMI and NOR serum levels (237.1 [119.9] vs 126.4 [52.8] ng/mL) and NOR/AMI ratio (1.300 [0.905] vs 0.865 [0.455]) was significantly higher. Both AMI and VPA are widely prescribed drugs. A combination of both is common for psychiatric or neurologic patients. A cautious dosing of AMI with VPA comedication is advisable, and therapeutic drug monitoring should be performed because this combination may lead to a remarkable increase of AMI and NOR serum levels.

Hematological effects of valproate in psychiatric patients: what are the risk factors?

BACKGROUND

Sodium valproate is an anticonvulsant that is also one of the common treatments used for bipolar disorder. The present study was conducted in psychiatric patients with the aim of examining the effects of valproate on hematological parameters and to explore any association with sex and age.

METHODS

A list of all psychiatric patients who underwent valproate level estimation in the years 2004-2008 in Newcastle upon Tyne was drawn from the biochemistry database of the local hospital. The names and date of births of these patients were used to draw corresponding hematological data, including hemoglobin, white blood cell count, mean corpuscular volume (MCV), and platelet count, conducted on the same day or within a week of the valproate level measurement.

RESULTS

: The data from 126 patients were analyzed. The prevalence of thrombocytopenia (platelet count, <150,000/microL) was found to be approximately 5%. In female subjects, a significant negative correlation was found between serum valproate level and platelet count; also, a positive correlation between valproate level and MCV was found. Neither correlation was found in male subjects. The risk of a low platelet count was found to be significantly increased at serum valproate level above 80 microg/mL in female subjects. The regression analysis in female patients showed a trend toward fall in platelet count and an increase in MCV with increasing age.

CONCLUSIONS

In psychiatric patients on valproate therapy, close monitoring of full blood count is required in women particularly at valproate serum level above 80 microg/mL. This may be particularly important in older patients.

Inhibition of histone deacetylase activity on specific embryonic tissues as a new mechanism for teratogenicity

BACKGROUND

the inhibition of histone deacetylase (HDAC) has been reported as an effective mechanism on therapy in neoplastic diseases. Among HDAC inhibitors, Trichostatin A (TSA) and Valproic Acid (VPA) prevent the tumorigenesis in rodent and human models. Malformations as neural tube and axial skeletal defects are well-known VPA side effects. Recent hypotheses suggest the HDAC inhibitor activity as the teratogenic mechanism of VPA. The teratogenic potency of TSA is, at the moment, unknown. The aim of the present work is to investigate the HDAC inhibition on embryos exposed in utero to TSA or VPA and to compare the teratogenic potential of these two molecules on the axial skeleton morphogenesis.

METHODS

Pregnant CD mice were i.p. treated on day 8 post coitum (9.00 a.m.) with 400 mg/kg VPA or with 0, 2, 4, 8, 16 mg/kg TSA. Embryos explanted 1 hr after the treatment from some females exposed to 400 mg/kg VPA or to 16 mg/kg TSA were processed for Western blotting and immunohistochemical analysis, in order to evaluate the histone hyperacetylation in the total embryo homogenates and to visualize the hyperacetylated tissues. Foetuses at term were processed for skeletal examination.

RESULTS

Both VPA and TSA were able to induce hyperacetylation on embryos, specifically at the level of the caudal neural tube and of somites. At term, TSA showed teratogenic effects at the axial skeleton, quite similar to those observed after VPA exposure.

CONCLUSIONS

In conclusion, both VPA and TSA are teratogenic in mice. A direct correlation between somite hyperacetylation and axial abnormalities could suggest the HDAC inhibition as the mechanism of the teratogenic effects.

Anti-tumor mechanisms of valproate: a novel role for an old drug

Valproic acid (VPA, 2-propylpentanoic acid) is an established drug in the long-term therapy of epilepsy. During the past years, it has become evident that VPA is also associated with anti-cancer activity. VPA not only suppresses tumor growth and metastasis, but also induces tumor differentiation in vitro and in vivo. Several modes of action might be relevant for the biological activity of VPA: (1) VPA increases the DNA binding of activating protein-1 (AP-1) transcription factor, and the expression of genes regulated by the extracellular-regulated kinase (ERK)-AP-1 pathway; (2) VPA downregulates protein kinase C (PKC) activity; (3) VPA inhibits glycogen synthase kinase-3beta (GSK-3beta), a negative regulator of the Wnt signaling pathway; (4) VPA activates the peroxisome proliferator-activated receptors PPARgamma and delta; (5) VPA blocks HDAC (histone deacetylase), causing hyperacetylation. The findings elucidate an important role of VPA for cancer therapy. VPA might also be useful as low toxicity agent given over long time periods for chemoprevention and/or for control of residual minimal disease.