Pharmacokinetics of oxcarbazepine and carbamazepine in human placenta

Variability in perfusion conditions and set-up parameters used in ex vivo human placenta models: A literature review

The ex vivo human placenta perfusion model has proven to be clinically relevant to study transfer- and fetal exposure of various drugs. Although the method has existed for a long period, the setup of the perfusion model has not been generalized yet. This review aims to summarize the setups of ex vivo placental perfusion models used to examine drug transfer across the placenta to identify generalized properties and differences across setups. A literature search was carried out in PubMed September 26, 2022. Studies were labeled as relevant when information was reported, between 2000 and 2022, on the setups of ex vivo placental perfusion models used to study drug transfer across the placenta. The placenta perfusion process, and the data extraction, was divided into phases of preparation, control, drug, and experimental reflecting the chronological timeline of the different phases during the entire placental perfusion process. 135 studies describing an ex vivo human placental perfusion experiment were included. Among included studies, the majority (78.5%) analyzed drug perfusion in maternal to fetal direction, 18% evaluated bi-directional drug perfusion, 3% under equilibrium conditions, and one study investigated drug perfusion in fetal to maternal direction. This literature review facilitates the comparison of studies that employ similar placenta perfusion protocols for drug transfer studies and reveals significant disparities in the setup of these ex vivo placental perfusion models. Due to interlaboratory variability, perfusion studies are not readily comparable or interchangeable. Therefore, a stepwise protocol with multiple checkpoints for validating placental perfusion is needed.

Physiologically based pharmacokinetic modeling to predict maternal pharmacokinetics and fetal carbamazepine exposure during pregnancy

Carbamazepine is an antiepileptic drug commonly used in pregnant women, during which the physiological changes may affect its efficacy. The aim of this study was to establish a physiologically based pharmacokinetic (PBPK) model of carbamazepine and its active metabolite carbamazepine-10,11-epoxide, and simulate maternal and fetal pharmacokinetic changes of carbamazepine and carbamazepine-10,11-epoxide in different trimesters and propose dose adjustment. We established pregnancy PBPK models for carbamazepine and carbamazepine-10,11-epoxide in PK-Sim® and Mobi® and validated the models with observed data from clinical reports. The placental transfer parameters obtained using different methods were also imported into the model and compared with the observed data to establish and validate fetal pharmacokinetic curves. The simulated results showed that mean steady-state trough plasma concentration of carbamazepine decreased by 27, 43.1, and 52 % during the first, second, and third trimesters, respectively. Therefore, to achieve an optimum therapeutic concentration, administering at least 1.4, 1.8, and 2.1 times the baseline dose of carbamazepine in the first, second, and third trimesters, respectively can be used as a dose reference. In conclusion, this study established and validated a pregnancy PBPK model of carbamazepine and carbamazepine-10,11-epoxide to assess exposure in pregnant women and fetuses, which provided a reference for the dosage adjustment of carbamazepine during pregnancy.

Transfer of anticonvulsants and lithium into amniotic fluid, umbilical cord blood & breast milk: A systematic review & combined analysis

OBJECTIVE

Data on the ability of anticonvulsants and lithium to enter fetal and newborn circulation has become increasingly available; here we estimated penetration ratios in a series of matrices from combined samples of pregnant/breastfeeding women treated with anticonvulsants or lithium.

METHODS

We conducted a systematic literature search in PubMed/EMBASE for studies with concentrations of anticonvulsants/lithium from maternal blood, amniotic fluid, umbilical cord blood and/or breast milk. Penetration ratios were calculated by dividing the concentrations in amniotic fluid, umbilical cord plasma or breast milk by the maternal concentrations. When data from multiple studies were available, we calculated combined penetration ratios, weighting studies' mean by study size.

RESULTS

Ninety-one eligible studies for brivaracetam, carbamazepine, clonazepam, ethosuximide, gabapentin, lacosamide, lamotrigine, levetiracetam, lithium, oxcarbazepine, perampanel, phenobarbital, phenytoin, pregabalin, primidone, topiramate, valproate, vigabatrin and zonisamide were identified. For amniotic fluid, the highest penetration ratios were estimated for levetiracetam (mean 3.56, range 1.27-5.85, n = 2) and lowest for valproate (mean 0.11, range 0.02-1.02, n = 57). For umbilical cord plasma, oxcarbazepine had the highest ratio (mean 1.59, range 0.11-4.33, n = 12) with clonazepam having the lowest (mean 0.55, range 0.52-0.59, n = 2). For breast milk, the highest ratios were observed for oxcarbazepine (mean 3.75, range 0.5-7.0, n = 2), whereas the lowest were observed for valproate (mean 0.04, range 0.01-0.22, n = 121).

DISCUSSION

We observed substantial variability between anticonvulsants and lithium regarding their ability to enter fetal/newborn circulation. Assessing concentrations of anticonvulsants and lithium in maternal samples can provide a surrogate of fetal/infant exposure, although patterns of concentration-dependent effects for maternal/neonatal safety are lacking.

Targeting adverse effects of antiseizure medication on offspring: current evidence and new strategies for safety

INTRODUCTION

For women with epilepsy of reproductive age, antiseizure medications (ASMs) are associated with an increased risk of offspring malformations. There are safety concerns for most anti-seizure medications in the perinatal period, and there is a clear need to identify safe medications. ASMs must transport through biological barriers to exert toxic effects on the fetus, and transporters play essential roles in trans-barrier drug transport. Therefore, it is vital to understand the distribution and properties of ASM-related transporters in biological barriers.

AREAS COVERED

This study reviews the structure, transporter distribution, and properties of the blood-brain, placental, and blood-milk barrier, and summarizes the existing evidence for the trans-barrier transport mechanism of ASMs and standard experimental models of biological barriers.

EXPERT OPINION

Ideal ASMs in the perinatal period should have the following characteristics: 1) Increased transport through the blood-brain barrier, and 2) Reduced transport of the placental and blood-milk barriers. Thus, only low-dose or almost no antiseizure medication could enter the fetus's body, which could decrease medication-induced fetal abnormalities. Based on the stimulated structure and molecular docking, we propose a development strategy for new ASMs targeting transporters of biological barriers to improve the perinatal treatment of female patients with epilepsy.

Application of Physiologically Based Pharmacokinetic Modeling to Predict Maternal Pharmacokinetics and Fetal Exposure to Oxcarbazepine

Pregnancy is associated with physiological changes that may affect drug pharmacokinetics (PKs). The aim of this study was to establish a maternal-fetal physiologically based pharmacokinetic (PBPK) model of oxcarbazepine (OXC) and its active metabolite, 10,11-dihydro-10-hydroxy-carbazepine (MHD), to (1) assess differences in pregnancy, (2) predict changes in PK target parameters of these molecules following the current dosing regimen, (3) assess predicted concentrations of these molecules in the umbilical vein at delivery, and (4) compare different methods for estimating drug placental penetration. Predictions using the pregnancy PBPK model of OXC resulted in maternal concentrations within a 2-fold error, and extrapolation of the model to early-stage pregnancies indicated that changes in median PK parameters remained above target thresholds, requiring increased frequency of monitoring. The dosing simulation results suggested dose adjustment in the last two trimesters. We generally recommend that women administer ≥ 1.5× their baseline dose of OXC during their second and third trimesters. Test methods for predicting placental transfer showed varying performance, with the in vitro method showing the highest predictive accuracy. Exposure to MHD in maternal and fetal venous blood was similar. Overall, the above-mentioned models can enhance understanding of the maternal-fetal PK behavior of drugs, ultimately informing drug-treatment decisions for pregnant women and their fetuses.

Lacosamide effects on placental carriers of essential compounds in comparison with valproate: Studies in perfused human placentas

OBJECTIVE

Lacosamide is increasingly being prescribed to pregnant women, although its effects on the developing fetus have not been fully clarified yet. Previously, we have shown that several antiseizure medications, particularly valproate, can affect the expression of carriers of essential compounds in placental cells. Here, our aim was to assess the effect of short ex vivo exposure of human placentas to lacosamide on the expression of carriers of essential nutrients required by the human fetus.

METHODS

Placentas were obtained from cesarean deliveries of women with no known epilepsy. Cotyledons were cannulated and perfused over 180 min in the presence of lacosamide at 2.5 μg/ml (10 μmol·L^-1 , n = 7) or 10 μg/ml (40 μmol·L^-1 , n = 6), representing low and high therapeutic concentrations, respectively, in the maternal perfusate. Valproate (83 μg/ml, 500 μmol·L^-1 , n = 6) and the perfusion solution (n = 6) were used as the respective positive and negative controls. A customized gene panel array was used to analyze the expression of carrier genes in the perfused cotyledons.

RESULTS

Following a 3-h perfusion, the mRNA expression of SLC19A1 (encoding the reduced folate carrier 1) was downregulated in placentas treated with 10 μg/ml lacosamide (50%) as compared with the vehicle (p < .05). Across all groups, a significant difference was observed in the expression of SLC19A3 (thiamine transporter 2; 52%, 20%, and 9% decrease by 10 μg/ml lacosamide, 83 μg/ml valproate, and 2.5 μg/ml lacosamide, respectively; p < .05).

SIGNIFICANCE

Lacosamide at high therapeutic concentrations exerted pharmacological effects on the human placenta. Our findings, if manifested in vivo, suggest that lacosamide could potentially affect folate supply to the fetus and support therapeutic monitoring and careful adjustment of lacosamide plasma concentrations during pregnancy.

The role of xenobiotic-metabolizing enzymes in the placenta: a growing research field

Introduction: The placenta is a temporary and unique organ that allows for the physical connection between a mother and fetus; this organ regulates the transport of gases and nutrients mediating the elimination of waste products contained in the fetal circulation. The placenta performs metabolic and excretion functions, on the basis of multiple enzymatic systems responsible for the oxidation, reduction, hydrolysis, and conjugation of xenobiotics. These mechanisms give the placenta a protective role that limits the fetal exposure to harmful compounds. During pregnancy, some diseases require uninterrupted treatment even if it is detrimental to the fetus. Drugs and other xenobiotics alter gene expression in the placenta with repercussions for the fetus and mother's well-being.Areas covered: This review provides a brief description of the human placental structure and function, the main drug and xenobiotic transporters and metabolizing enzymes, placenta-metabolized substrates, and alterations in gene expression that the exposure to xenobiotics may cause.Expert opinion: Research should be focused on the identification and validation of biological markers for the assessment of the harmful effects of some drugs in pregnancy, including the evaluation of polymorphisms and methylation patterns in chorionic villous samples and/or amniotic fluid.

Effect of epilepsy in pregnancy on fetal growth restriction: a systematic review and meta-analysis

PURPOSE

Epilepsy is one of the most common neurological diseases during pregnancy. However, the influence of epilepsy on fetal growth is not understood. Thus, this study conducted a meta-analysis to determine the influence of epilepsy during pregnancy on fetal growth restriction (FGR).

METHODS

BIOSIS, Medline, Embase, and PubMed databases were searched between January 2000 and January 2016. Without imposing language or regional restrictions, referenced articles were selected.

RESULTS

Final analysis included 684 citations from 11 studies. Estimated risk of FGR was 1.28-fold higher in epileptic pregnant women than in non-epileptic women [95% confidence interval (95% CI) 1.09-1.50, p < 0.05]. Given the course of previous studies, hierarchical analysis of pregnant women who use antiepileptic drugs (AEDs) was conducted. Results show that FGR rate is significantly increased even if AEDs were taken [odds ratio 1.26, 95% CI 1.13-1.41, p < 0.05].

CONCLUSIONS

Although modest bias cannot be avoided, our meta-analysis indicated that epilepsy participates in fetal development as an unfavorable factor, and AEDs seemed to be useless in decreasing the occurrence rate of FGR.

Epilepsy during pregnancy: focus on management strategies

In the US, more than one million women with epilepsy are of childbearing age and have over 20,000 babies each year. Patients with epilepsy who become pregnant are at risk of complications, including changes in seizure frequency, maternal morbidity and mortality, and congenital anomalies due to antiepileptic drug exposure. Appropriate management of epilepsy during pregnancy may involve frequent monitoring of antiepileptic drug serum concentrations, potential preconception switching of antiepileptic medications, making dose adjustments, minimizing peak drug concentration with more frequent dosing, and avoiding potentially teratogenic medications. Ideally, preconception planning will be done to minimize risks to both the mother and fetus during pregnancy. It is important to recognize benefits and risks of current and emerging therapies, especially with revised pregnancy labeling in prescription drug product information. This review will outline risks for epilepsy during pregnancy, review various recommendations from leading organizations, and provide an evidence-based approach for managing patients with epilepsy before, during, and after pregnancy.

Carbamazepine

This chapter includes the aspects of carbamazepine. The drug is synthesized by the use of 5H-dibenz[b,f]azepine and phosgene followed by subsequent reaction with ammonia. Carbamazepine is generally used for the treatment of seizure disorders and neuropathic pain, it is also important as off-label for a second-line treatment for bipolar disorder and in combination with an antipsychotic in some cases of schizophrenia when treatment with a conventional antipsychotic alone has failed. Other uses may include attention deficit hyperactivity disorder, schizophrenia, phantom limb syndrome, complex regional pain syndrome, borderline personality disorder, and posttraumatic stress disorder. The chapter discusses the drug metabolism and pharmacokinetics and presents various methods of analysis of this drug such electrochemical analysis, spectroscopic analysis, and chromatographic techniques of separation. It also discusses its physical properties such as solubility characteristics, X-ray powder diffraction pattern, and thermal methods of analysis. The chapter is concluded with a discussion on its biological properties such as activity, toxicity, and safety.

Reducing PEC uncertainty in coastal zones: a case study on carbamazepine, oxcarbazepine and their metabolites

Concentrations of the antiepileptic drugs carbamazepine (Cbz), oxcarbazepine (OxCz) and their main metabolites were predicted in a wastewater treatment plant (WTP) and in the vicinity of its submarine outfall located in a Mediterranean coastal zone. Refined predicted environmental concentrations (PECs) were calculated in effluents based on consumption data and human excretion rates. PECs were estimated in the sea using the hydrodynamic MARS 3D model integrating meteorological data, oceanic conditions (wind, tide, atmospheric pressure), freshwater and sewage inputs. Measured environmental concentrations (MECs) were compared to PECs to assess the estimation relevance. In the coastal zone, PEC and MEC were in the same magnitude range. Modeling of Cbz diffusion and advection just above the submarine outfall showed the influence of the thermocline during summer, with low diffusion of Cbz from the bottom to the surface. This work allowed understanding the dispersion of target compounds and deserved further development for a better acknowledgement of vulnerability at local scales.

Diabetes and hypertension increase the placental and transcellular permeation of the lipophilic drug diazepam in pregnant women

Background

Previous studies carried out in our laboratories have demonstrated impaired drug permeation in diabetic animals. In this study the permeation of diazepam (after a single dose of 5 mg/day, administered intramuscularly) will be investigated in diabetic and hypertensive pregnant women.

Methods

A total 75 pregnant women were divided into three groups: group 1 (healthy control, n = 31), group 2 (diabetic, n = 14) and group 3 (hypertensive, n = 30). Two sets of diazepam plasma concentrations were collected and measured (after the administration of the same dose of diazepam), before, during and after delivery. The first set of blood samples was taken from the mother (maternal venous plasma). The second set of samples was taken from the fetus (fetal umbilical venous and arterial plasma). In order to assess the effect of diabetes and hypertension on diazepam placental-permeation, the ratios of fetal to maternal blood concentrations were determined. Differences were considered statistically significant if p ≤ 0.05.

Results

The diabetes and hypertension groups have 2-fold increase in the fetal umbilical-venous concentrations, compared to the maternal venous concentrations. Feto: maternal plasma-concentrations ratios were higher in diabetes (2.01 ± 1.10) and hypertension (2.26 ± 1.23) groups compared with control (1.30 ± 0.48) while, there was no difference in ratios between the diabetes and hypertension groups. Umbilical-cord arterial: venous ratios (within each group) were similar among all groups (control: 0.97 ± 0.32; hypertension: 1.08 ± 0.60 and diabetes: 1.02 ± 0.77).

Conclusions

On line with our previous findings which demonstrate disturbed transcellular trafficking of lipophilic drugs in diabetes, this study shows significant increase in diazepam placental-permeation in diabetic and hypertensive pregnant women suggesting poor transcellular control of drug permeation and flux, and bigger exposure of the fetus to drug-placental transport.

Ex vivo perfusion of mid-to-late-gestation mouse placenta for maternal-fetal interaction studies during pregnancy

Ex vivo perfusion systems offer a reliable, reproducible method for studying acute physiological responses of an organ to various environmental manipulations. Unlike in vitro culture systems, the cellular organization, compartmentalization and three-dimensional structure of ex vivo-perfused organs are maintained. These particular parameters are crucial for the normal physiological function of the placenta, which supports fetal growth through transplacental exchange, nutritional synthesis and metabolism, growth factor promotion and regulation of both maternally and fetally derived molecules. The perfusion system described here, which can be completed in 4-5 h, allows for integrated, physiological studies of de novo synthesis and metabolism and transport of materials across the live mouse placenta, not only throughout a normal gestation period but also following a variety of individual or combined genetic and environmental perturbations compromising placental function.

Drug Interactions at the Human Placenta: What is the Evidence?

Pregnant women (and their fetuses) are treated with a significant number of prescription and non-prescription medications. Interactions among those drugs may affect their efficacy and toxicity in both mother and fetus. Whereas interactions that result in altered drug concentrations in maternal plasma are detectable, those involving modulation of placental transfer mechanisms are rarely reflected by altered drug concentrations in maternal plasma. Therefore, they are often overlooked. Placental-mediated interactions are possible because the placenta is not only a passive diffusional barrier, but also expresses a variety of influx and efflux transporters and drug-metabolizing enzymes. Current data on placental-mediated drug interactions are limited. In rodents, pharmacological or genetic manipulations of placental transporters significantly affect fetal drug exposure. In contrast, studies in human placentae suggest that the magnitude of such interactions is modest in most cases. Nevertheless, under certain circumstances, such interactions may be of clinical significance. This review describes currently known mechanisms of placental-mediated drug interactions and the potential implications of such interactions in humans. Better understanding of those mechanisms is important for minimizing fetal toxicity from drugs while improving their efficacy when directed to treat the fetus.

The human placental perfusion model: a systematic review and development of a model to predict in vivo transfer of therapeutic drugs

Dual perfusion of a single placental lobule is the only experimental model to study human placental transfer of substances in organized placental tissue. To date, there has not been any attempt at a systematic evaluation of this model. The aim of this study was to systematically evaluate the perfusion model in predicting placental drug transfer and to develop a pharmacokinetic model to account for nonplacental pharmacokinetic parameters in the perfusion results. In general, the fetal-to-maternal drug concentration ratios matched well between placental perfusion experiments and in vivo samples taken at the time of delivery of the infant. After modeling for differences in maternal and fetal/neonatal protein binding and blood pH, the perfusion results were able to accurately predict in vivo transfer at steady state (R² = 0.85, P < 0.0001). Placental perfusion experiments can be used to predict placental drug transfer when adjusting for extra parameters and can be useful for assessing drug therapy risks and benefits in pregnancy.

Cytochrome P450 3As gene expression and testosterone 6 beta-hydroxylase activity in human fetal membranes and placenta at full term

Expression levels of cytochrome P450 (CYP) 3A4, CYP3A5 and CYP3A7 mRNAs in placentas and fetal membranes, which were split into amnion and chorion leave attached decidua (chorion/decidua), obtained from pregnant women with normal delivery (5 subjects) and Caesarean section (15 subjects) were determined. These CYP3A mRNAs were also expressed in amnion and chorion/decidua together with placenta, although the expression level of these mRNAs was strikingly different between subjects. The expression level of the CYP3A4 mRNA in the placenta was about 2-fold higher than those in amnion and chorion/decidua. On the other hand, the expression levels of CYP3A5 and CYP3A7 mRNAs were highest in chorion/decidua. The immunologically related protein(s) with CYP3A7 was detected in all tissues examined. Testosterone 6beta-hydroxylase activity in homogenate of human placenta, amnion and chorion/decidua were 26.6, 3.7 and 4.6 pmol/h/mg protein, respectively. These results suggest that CYP3As in fetal membranes have the metabolic function to protect the fetus from exposure to drugs.

Placental transfer and DNA binding of benzo(a)pyrene in human placental perfusion

Benzo(a)pyrene (BP) is the best studied polycyclic aromatic hydrocarbon, classified as carcinogenic to humans. The carcinogenic metabolite, benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE), binds covalently to DNA. The key enzyme in this metabolic reaction is CYP1A1, which has also been found in placenta and human trophoblastic cells. By using human placental perfusion we confirmed that BP added to the maternal circulation in concentrations of 0.1 and 1 microM reaches fetal compartment but somewhat slower than the freely diffusible reference substance antipyrine. A well-known P-glycoprotein (ABCB1/P-gp) antagonist verapamil did not affect the transfer more than it did in the case of antipyrine, indicating that ABCB1/P-gp does not have a role in BP transfer. In one of the two placentas perfused for 6 h with the higher concentration of BP (1 microM) BPDE specific DNA adducts were found in placental tissue after the perfusion, but not before. The ability of human trophoblastic cells to activate BP to BPDE-DNA adducts was confirmed in human trophoblastic BeWo cells. This study shows that maternal exposure to BP leads to the exposure of the fetus to BP and/or its metabolites and that placenta itself can activate BP to DNA adducts.

Pregnancy and epilepsy management and outcome: an update

Epilepsy affects one in 100 individuals. Although epilepsy is gender neutral, women face more challenges with regard to treatment than men. Treatment of women with epilepsy is a therapeutic challenge since they are unlikely to be medication free. An estimated 1 million women with epilepsy are of childbearing age. Each year, approximately 20,000 births occur in women with epilepsy. Despite these challenges, over 90% of women with epilepsy have normal healthy outcomes. Ensuring seizure control is of utmost importance to the health of the mother and fetus. Serum concentrations of antiepileptic drug (AED) decrease during pregnancy resulting in an increased risk of seizure activity, which may result in serious consequences such as maternal injury or fetal and/or maternal demise. Teratogenicity secondary to AED drug exposure has long been reported, especially with the older AEDs, and to some degree with newer agents. More recently, the discovery of long-term cognitive impairment has been reported in offspring exposed to valproate in utero. Choice of AED must balance seizure control with minimizing the risk of malformations and other health issues. Prenatal planning is warranted whenever possible in order to address these concerns. Supplementation with folic acid pregestationally may be helpful in preventing malformations such as spina bifida.

In Vitro Models Using the Human Placenta to Study Fetal Exposure to Drugs

Over the recent years there has been a gradual rise in the use of pharmaceuticals during pregnancy. Knowledge on placental drug transfer and metabolism has increased during the past decades as well. Investigation of the transplacental transfer of any therapeutically useful drug is essential to the understanding of its metabolic processes and is a prerequisite for its use during pregnancy. The purpose of this review is to give insight on the various techniques that have been developed to evaluate transplacental transfer of drugs and xenobiotics.

The human placenta – An alternative for studying foetal exposure

Pregnant women are daily exposed to a wide selection of foreign substances. Sources are as different as lifestyle factors (smoking, daily care products, alcohol consumption, etc.), maternal medication or occupational/environmental exposures. The placenta provides the link between mother and foetus, and though its main task is to act as a barrier and transport nutrients and oxygen to the foetus, many foreign compounds are transported across the placenta to some degree and may therefore influence the unborn child. Foetal exposures to environmental and medicinal products may have impact on the growth of the foetus (e.g. cigarette smoke) and development of the foetal organs (e.g. methylmercury and thalidomide). The scope of this review is to give insight to the placental anatomy, development and function. Furthermore, the compounds physical properties and the transfer mechanism across the placental barrier are evaluated. In order to determine the actual foetal risk from exposure to a chemical many studies regarding the topic are necessary, including means of transportation, toxicological targets and effects. For this purpose several in vivo and in vitro models including the placental perfusion system are models of choice.

The fate and effects of xenobiotics in human placenta

During past decades, knowledge on placental drug metabolism and mechanisms of placental transfer has increased significantly. Most pharmaceutical drugs administered during pregnancy cross the placenta to some extent. The important properties determining the placental transfer by passive diffusion are molecular weight, pK(a), lipid solubility and protein binding. In addition to passive diffusion, compounds may cross the placenta via active transfer, facilitated diffusion, phagocytosis and pinocytosis. This review gives an update of efflux transporter proteins and xenobiotic-metabolizing enzymes that modify the fate and effects of drugs in the placenta.

Safety of the newer antiepileptic drug oxcarbazepine during pregnancy

OBJECTIVE

Seizure control in pregnant women with epilepsy is vital, as maternal seizures may have deleterious consequences. The treatment of pregnant women with epilepsy is, however, complicated by the teratogenicity of older antiepileptic drugs (AEDs). In this review, the safety of the newer AED oxcarbazepine during pregnancy is assessed based on published pregnancy outcome data. Other relevant safety issues, such as oxcarbazepine pharmacokinetics during pregnancy and the compatibility of oxcarbazepine treatment with breastfeeding, are also discussed.

METHODS

Literature searches of the following databases were performed: MEDLINE, EMBASE, eNova, NOWIMA (an internal Novartis Germany database), Derwent Drug File, SciSearch and BIOSIS. Identified publications were examined for original data reporting rates of foetal malformation following maternal exposure to oxcarbazepine as monotherapy or adjunctive therapy.

RESULTS

Relevant publications reporting data from the worldwide Novartis safety database and pregnancy registries or study centres in six countries were identified. A total of 248 pregnancies involving maternal exposure to oxcarbazepine monotherapy and 61 involving adjunctive therapy were reported. There were six malformations among the monotherapy group, equating to a malformation rate of 2.4% (6/248). The malformation rate reported in the general population is 2-4%. There were four malformations associated with oxcarbazepine adjunctive therapy, equating to a malformation rate of 6.6% (4/61).

CONCLUSIONS

This literature review suggests that, compared with newborns in the general population, the newborns of women receiving oxcarbazepine monotherapy during pregnancy do not appear to show an increased risk for malformations. However, the number of pregnancies involving maternal exposure to oxcarbazepine identified by this review is not sufficient to draw definitive conclusions. Additional information from large-scale pregnancy registries is required to confirm the safety profile of oxcarbazepine as monotherapy or adjunctive therapy during pregnancy.

Oxcarbazepine: current status and clinical applications

Oxcarbazepine (OXC) was introduced in 1990 and is now registered in 54 countries worldwide as monotherapy, as add-on treatment for partial seizures, with or without secondarily generalised seizures, and primary generalised tonic-clonic seizures. OXC and its active metabolite, monohydroxy derivative (MHD), block voltage-dependent sodium channels and may effect potassium and calcium channels. In animal models of epilepsy, OXC and MHD have efficacy similar to that of CBZ. There is no evidence for clinically important teratogenicity, mutagenicity or carcinogenicity. OXC has no effect on serum concentrations of hepatically metabolised anti-epileptic drugs (AEDs) and no clinically important interactions with common non-AEDs, other than hormonal contraceptives. MHD has low protein binding and linear pharmacokinetics. Adverse effects (AEs) are usually related to the central nervous system. Approximately three-quarters of patients who experience adverse effects with CBZ improve when switched to OXC, without loss of seizure control. The incidence of rash appears to be less than that expected with CBZ. While hyponatraemia may occur more often with OXC than with CBZ, it is rarely symptomatic. OXC is an effective and safe drug for the treatment of partial-onset and primary generalised tonic-clonic seizures. Placebo- and low-dose controlled double-blind monotherapy studies prove that OXC has anticonvulsant activity and that therapeutic dosages may be obtained with a 24 h titration in hospitalised patients, if necessary. Comparative double-blind trials show that OXC has similar efficacy to VPA, CBZ and PHT, but has advantages compared to those agents in terms of pharmacokinetics, side-effects and tolerability.

What is the evidence that oxcarbazepine and carbamazepine are distinctly different antiepileptic drugs?

Oxcarbazepine (OXC, Trileptal) is a modern antiepileptic drug (AED) used as both monotherapy and adjunctive therapy for the treatment of partial seizures with or without secondary generalization in adults and children above 4 years (USA) or 6 years (Europe) of age. Although OXC has been developed through structural variation of carbamazepine (CBZ) with the intent to avoid metabolites causing side effects, significant differences have emerged between the two drugs. The mechanism of action of OXC involves mainly blockade of sodium currents but differs from CBZ by modulating different types of calcium channels. In contrast to CBZ, which is oxidized by the cytochrome P-450 system, OXC undergoes reductive metabolism at its keto moiety to form the monohydroxy derivative (MHD), which is glucuronidated and excreted in the urine. The involvement of the hepatic cytochrome P-450-dependent enzymes in the metabolism of OXC is minimal. Although it does not prevent interaction with oral contraceptives, it explains why OXC can be more effectively combined with other AEDs such as valproate compared with CBZ. Switching from CBZ to OXC normalized CBZ-associated thyroid and sexual hormone abnormalities and pathological lipid values in small patient samples. OXC is often better tolerated than CBZ and causes fewer rashes than CBZ. Add-on or substitution treatment with OXC was effective in controlled trials even when CBZ did not achieve sufficient seizure control. This constitutes compelling clinical evidence that OXC and CBZ are distinctly different medications. From postmarketing experience in over 1,000,000 patient years, OXC had an advantageous risk-benefit balance also in comparison to other new AEDs. OXC should be preferred over CBZ and other older AEDs because of its proven efficacy and excellent side effect profile in children, adolescents, and adults with partial seizures.

Clinical pharmacokinetics of oxcarbazepine

Oxcarbazepine is an antiepileptic drug with a chemical structure similar to carbamazepine, but with different metabolism. Oxcarbazepine is rapidly reduced to 10,11-dihydro-10-hydroxy-carbazepine (monohydroxy derivative, MHD), the clinically relevant metabolite of oxcarbazepine. MHD has (S)-(+)- and the (R)-(-)-enantiomer, but the pharmacokinetics of the racemate are usually reported. The bioavailability of the oral formulation of oxcarbazepine is high (>95%). It is rapidly absorbed after oral administration, reaching peak concentrations within about 1-3 hours after a single dose, whereas the peak of MHD occurs within 4-12 hours. At steady state, the peak of MHD occurs about 2-4 hours after drug intake. The plasma protein binding of MHD is about 40%. Cerebrospinal fluid concentrations of MHD are in the same range as unbound plasma concentrations of MHD. Oxcarbazepine can be transferred significantly through the placenta in humans. Oxcarbazepine and MHD exhibit linear pharmaco-kinetics and no autoinduction occurs. Elimination half-lives in healthy volunteers are 1-5 hours for oxcarbazepine and 7-20 hours for MHD. Longer and shorter elimination half-lives have been reported in elderly volunteers and children, respectively. Mild to moderate hepatic impairment does not appear to affect MHD pharmacokinetics. Renal impairment affects the pharmacokinetics of oxcarbazepine and MHD. The interaction potential of oxcarbazepine is relatively low. However, enzyme-inducing antiepileptic drugs such as phenytoin, phenobarbital or carbamazepine can reduce slightly the concentrations of MHD. Verapamil may moderately decrease MHD concentrations, but this effect is probably without clinical relevance. The influence of oxcarbazepine on other antiepileptic drugs is not clinically relevant in most cases. However, oxcarbazepine appears to increase concentrations of phenytoin and to decrease trough concentrations of lamotrigine and topiramate. Oxcarbazepine lowers concentrations of ethinylestra-diol and levonorgestrel, and women treated with oxcarbazepine should consider additional contraceptive measures. Due to the absent or lower enzyme-inducing effect of oxcarbazepine, switching from carbamazepine to oxcarbazepine can result in increased serum concentrations of comedication, sometimes associated with adverse effects. The effect of oxcarbazepine appears to be related to dose and to serum concentrations of MHD. In general, daily fluctuations of MHD concentration are relatively slight, smaller than would be expected from the elimination half-life of MHD. However, relatively high fluctuations can be observed in individual patients. Therapeutic monitoring may help to decide whether adverse effects are dependent on MHD concentrations. A mean therapeutic range of 15-35 mg/L for MHD seems to be appropriate. However, more systematic studies exploring the concentration-effect relationship are required.

Overview of the Clinical Pharmacokinetics of Oxcarbazepine

Oxcarbazepine (GP 47680, 10,11-dihydro-10-oxo-5H-dibenz[b,f]azepine- 5-carboxamide) is an antiepileptic drug registered worldwide by Novartis under the trade name Trileptal((R)). Trileptal((R))is approved as adjunctive therapy or monotherapy for the treatment of partial seizures in adults and in children. In the US, Trileptal((R)) is approved as adjunctive therapy in adults and in children >/=4 years of age and as monotherapy in adults and in children.Trileptal((R))is currently marketed as 150, 300 and 600mg film-coated tablets for oral administration. A 60 mg/mL (6%) oral suspension formulation has also been registered worldwide.Oxcarbazepine and its pharmacologically active metabolite, 10-monohydroxy derivative (MHD; 10,11-dihydro-10-hydro-carbamazepine; GP 47779) show potent antiepileptic activity in animal models comparable to that of carbamazepine (Tegretol((R))) and phenytoin. Oxcarbazepine and MHD have been shown to exert antiepileptic activity by blockade of voltage-dependent sodium channels in the brain.Oxcarbazepine is rapidly reduced by cytosolic enzymes in the liver to MHD, which is responsible for the pharmacological effect of the drug. This step is mediated by cytosolic arylketone reductases. MHD is eliminated by conjugation with glucuronic acid. Minor amounts (4% of the dose) are oxidised to the pharmacologically inactive dihydroxy derivative (DHD). The absorption of oxcarbazepine is complete. In plasma after a single oral administration of oxcarbazepine the mean apparent elimination half-life (t((1/2))) of MHD in adults was 8-9h. Food has no effect on the bioavailability of the highest strength of the final market image tablet (600mg). At steady state MHD displays predictable linear pharmacokinetics at doses ranging from 300 to 2400mg. In children with normal renal function, renal clearance of MHD is higher than in adults, with a corresponding reduction in the terminal t((1/2)) of MHD. Consequently, although no special dose recommendation is needed, an increase in the dose of oxcarbazepine may be necessary to achieve similar plasma levels to those in adults. In patients with moderate to severe renal impairment (creatinine clearance <30 mL/min), the elimination t((1/2)) of MHD is prolonged with a corresponding 2-fold increase in area under the concentration-time curve. Therefore, a dose reduction of at least 50% and a prolongation of the titration period is necessary in these patients. Mild-to-moderate hepatic impairment does not affect the pharmacokinetics of MHD. Based on in vitro and in vivo findings and compared with antiepileptic drugs such as carbamazepine, phenytoin and phenobarbital, oxcarbazepine has a low propensity for drug-drug interactions. In vitro, MHD inhibits the cytochrome P450 (CYP) 2C19 (ki [inhibition constant] = 88 micromol/L). At oxcarbazepine doses above 1.2g, a 40% increase in the concentration of phenytoin and a 15% increase in phenobarbital levels were observed. Oxcarbazepine/MHD at high doses may slightly increase phenobarbital and phenytoin plasma concentrations. Therefore, when using high doses of oxcarbazepine an adjustment in the dose of phenytoin may be required. In vitro, MHD is only a weak inducer of uridine diphospate (UDP)-glucuronyltransferase (UDPGT) and therefore is unlikely to have an effect on drugs that are mainly eliminated by conjugation through the UDPGT enzymes (e.g. valproic acid and lamotrigine). Weak interactions between MHD and antiepileptic drugs that are strong inducers of CYP enzymes have been identified. Carbamazepine, phenobarbital and phenytoin have been shown to reduce MHD levels by 30-40% when coadministered with oxcarbazepine, with no decrease in efficacy. Oxcarbazepine decreases the plasma hormone levels (ethinylestradiol and levonorgestrel) of oral contraceptives and may therefore have the potential to cause oral contraception failure.

Drug Transfer and Metabolism by the Human Placenta

The major function of the placenta is to transfer nutrients and oxygen from the mother to the foetus and to assist in the removal of waste products from the foetus to the mother. In addition, it plays an important role in the synthesis of hormones, peptides and steroids that are vital for a successful pregnancy. The placenta provides a link between the circulations of two distinct individuals but also acts as a barrier to protect the foetus from xenobiotics in the maternal blood. However, the impression that the placenta forms an impenetrable obstacle against most drugs is now widely regarded as false. It has been shown that that nearly all drugs that are administered during pregnancy will enter, to some degree, the circulation of the foetus via passive diffusion. In addition, some drugs are pumped across the placenta by various active transporters located on both the fetal and maternal side of the trophoblast layer. It is only in recent years that the impact of active transporters such as P-glycoprotein on the disposition of drugs has been demonstrated. Facilitated diffusion appears to be a minor transfer mechanism for some drugs, and pinocytosis and phagocytosis are considered too slow to have any significant effect on fetal drug concentrations. The extent to which drugs cross the placenta is also modulated by the actions of placental phase I and II drug-metabolising enzymes, which are present at levels that fluctuate throughout gestation. Cytochrome P450 (CYP) enzymes in particular have been well characterised in the placenta at the level of mRNA, protein, and enzyme activity. CYP1A1, 2E1, 3A4, 3A5, 3A7 and 4B1 have been detected in the term placenta. While much less is known about phase II enzymes in the placenta, some enzymes, in particular uridine diphosphate glucuronosyltransferases, have been detected and shown to have specific activity towards marker substrates, suggesting a significant role of this enzyme in placental drug detoxification. The increasing experimental data on placental drug transfer has enabled clinicians to make better informed decisions about which drugs significantly cross the placenta and develop dosage regimens that minimise fetal exposure to potentially toxic concentrations. Indeed, the foetus has now become the object of intended drug treatment. Extensive research on the placental transfer of drugs such as digoxin and zidovudine has assisted with the safe treatment of the foetus with these drugs in utero. Improved knowledge regarding transplacental drug transfer and metabolism will result in further expansion of pharmacological treatment of fetal conditions.

Aromatase is the major enzyme metabolizing buprenorphine in human placenta

Buprenorphine (BUP) is a partial opiate agonist used for treatment of the adult and the pregnant addicted to this class of narcotics. The kinetic parameters for transplacental transfer and the metabolism of BUP during its perfusion in a placental lobule were the subject of an earlier report from our laboratory. The aim of this investigation is to identify and characterize the enzyme catalyzing the metabolism of BUP in term human placenta. Norbuprenorphine (norBUP) is the only metabolite formed as determined by high performance liquid chromatography and mass spectrometry. The activity of the enzyme responsible for BUP metabolism is highest in the microsomal fraction and lowest in the cytosolic, with the mitochondrial in between. Compounds with selective affinity to the enzyme aromatase (CYP 19), namely 4-hydroxyandrostenedione and aminoglutethimide, caused >70% inhibition of norBUP formation. Monoclonal antibodies raised against CYP 19 were the most potent inhibitors of BUP dealkylation. A comparison between the data obtained from the saturation isotherm for BUP dealkylation by placental microsomes and a commercially available system of cDNA-expressed CYP 19 indicated similar kinetic parameters, with apparent Km values of 12 +/- 4.0 and 14 +/- 8.0 microM, respectively. Therefore, aromatase is the major enzyme catalyzing the biotransformation of BUP to norBUP in term human placentas obtained from healthy pregnancies. The minor involvement of other cytochrome P450 isoforms or enzyme(s) in the metabolism of BUP in placental tissue cannot be ruled out.

Teratogenic potential of the newer antiepileptic drugs: what is known and how should this influence prescribing?

The treatment of women of childbearing age who have epilepsy raises many questions because of the interactions between epilepsy, antiepileptic therapy and different aspects of reproductive life. Menstrual cycle disorders and reduced fertility have been partially ascribed to antiepileptic drugs (AEDs). Furthermore, most AEDs induce the cytochrome P450 (CYP) enzymatic system, altering the metabolism of sex hormones and contributing to the failure of oral contraceptives. Pregnancy represents, in this context, the most critical period because of the well known teratogenic potential of all established AEDs. For most of these drugs no specific patterns of malformations have been identified, although during the past few decades basic knowledge has been acquired, particularly concerning the mechanisms of AED-induced teratogenesis and related risk factors. These issues form the basis of the current guidelines for the management of epilepsy in pregnant women. In the past decade, several new AEDs have been introduced into clinical practice. For a number of reasons, these drugs appear to be more favourable than the older ones as treatments for epilepsy in women of childbearing age. They possess a good pharmacokinetic profile that makes them more stable during pregnancy, and they have a low potential for interaction with other drugs. They are also less likely than the older AEDs to be metabolised to compounds that are teratogenic. Furthermore, most of them do not possess antifolate properties. With the exception of topiramate and vigabatrin, the newer AEDs do not appear to be teratogenic in animals when administered in subtoxic doses. However, animal teratology may not be a reliable predictor of human teratogenicity, and there is a significant lack of information regarding the teratogenic profile of these newer agents in humans. Because clinical experience with these agents is limited, it is advisable to avoid exposure of the embryo to these drugs when pregnancy is planned. The establishment of pregnancy registries could allow for the rapid collection of data related to the administration of new AEDs in pregnancy and the outcomes of such exposure.

Transplacental passage of lamotrigine in a human placental perfusion system in vitro and in maternal and cord blood in vivo

OBJECTIVE

We studied transplacental passage of lamotrigine (3,5-diamino-6-[2,3-dichlorophenyl]-1,2,4-triazine; LTG) using an ex vivo human placental perfusion method and in in vivo samples.

METHODS

Term placentas from healthy mothers without medications were perfused in a recirculating dual perfusion system. LTG (2.5 microg/ml, n=4; 10 microg/ml, n=4) and reference compound antipyrine (100 microg/ml) were added into the maternal circulation. The disappearance of drugs from the maternal circulation and appearance into the foetal circulation was followed every 15 min up to 2 h. Drug concentrations were analysed using high-performance liquid chromatography. In addition to human placental perfusions, we analysed LTG concentrations in maternal vein and cord blood samples after delivery from two epileptic mothers receiving LTG therapy during pregnancy.

RESULTS

LTG was detectable in the foetal circulation at 15 min in all of the perfusions, indicating rapid transfer. Maternal and foetal concentrations reached equilibrium at 60 min with both concentrations used. The feto-maternal ratio was 1.26+/-0.20 with 10 microg/ml LTG and 0.83+/-0.41 with 2.5 microg/ml LTG at the end of the perfusion. The transfer of LTG from the maternal to the foetal compartment at 120 min was 28.9+/-10.7% with 2.5 microg/ml LTG and 37.8+/-3.2% with 10 microg/ml LTG (p>0.05). In the serum samples from epileptic mothers, the cord blood maternal concentration ratio was 1.02 in one pair and 1.55 in the other.

CONCLUSIONS

LTG crossed the placenta easily and rapidly, indicating that the maternal treatment leads to a considerable foetal exposure.

An examination of whether human placental perfusion allows accurate prediction of placental drug transport: Studies with diazepam

INTRODUCTION

Presently, no well-validated predictive tools are available for human placental transfer. We studied the transplacental passage of diazepam (DZP) in a recirculating dual human placental perfusion and compared the data with in vivo clinical data from the literature.

METHODS

Term placentas from healthy mothers without medication were used. The dual, recirculating perfusion technique was used. DZP (2 microg/ml, n = 4; 200 ng/ml, n = 3) and the reference compound antipyrine (100 microg/ml) were added into the maternal circulation simultaneously. The disappearance of drugs from the maternal circulation and appearance into the fetal circulation were followed every 15 min for 2 h.

RESULTS

DZP was detectable in the fetal circulation within 15 min in all of the perfusions indicating rapid transfer. DZP concentrations in the maternal circulation were higher than in the fetal circulation throughout the perfusion with both initial concentrations. At the end of the perfusion, the feto-maternal ratio was 0.48 +/- 0.11 (mean +/- S.D.) and the transfer from the maternal to the fetal compartment 18.4 +/- 3.6% with 2 microg/ml of DZP and 0.55 +/- 0.10 and 20.5 +/- 3.1% with 200 ng/ml of DZP, respectively. DZP concentrations in the perfused area of the placenta were in average 2 times higher than in the maternal perfusate and 3.6 times higher than in the fetal perfusate. Total recovery of DZP from samples, perfusion fluid, and perfused tissue was 37.6 +/- 21%.

DISCUSSION

Since animal studies in vivo do not accurately predict human placental transfer and it is problematic to study placental transfer of drugs in humans in vivo, the present human placental perfusion system could serve as one part of a test battery for fetotoxicity. However, although our earlier studies and those from the literature indicate a good correlation between in vivo and placental perfusion data, the present study shows this is not the case for all drugs.

Octakis-6-sulfato-gamma-cyclodextrin as additive for capillary electrokinetic chromatography of dibenzoazepines: carbamazepine, oxcarbamazepine and their metabolites

Single isomer octakis-(2,3-dihydroxy-)6-sulfato-gamma-cyclodextrin used as pseudostationary phase of the background electrolyte interacts with dibenzo[b,f]azepines (consisting of a condensed 3-ring system) and forms negatively charged complexes. Hydroxygroups in position 2 and 3 at carbamazepine increase the extent of interaction, whereas substitution by oxygen at position 10 and/or 11 reduces it. The complex constants for the analytes are ranging from few tens L/mol (10-hydroxycarbamazepine, 10,11-dihydroxycarbamazepine, 10,11-epoxycarbamazepine, oxcarbazepine) to several hundreds L/mol (carbamazepine, 2-hydroxycarbamazepine, 3-hydroxycarbamazepine), and are much larger than those of the analytes with octakis-(2,3-dimethyl-)-6-sulfato-gamma-cyclodextrin. Full enantiomeric separation of the chiral metabolites of carbamazepine and oxcarbazepine is obtained at octakis-(2,3-dihydroxy-)-6-sulfato-gamma-cyclodextrin concentrations of about 10 mM (3 mM borate buffer, pH 8.5). Compared to heptakis-6-sulfato-beta-cyclodextrin, selectivity differs and stereoselectivity is more pronounced.

Gene transfer to human placenta ex vivo: a novel application of dual perfusion of human placental cotyledon

OBJECTIVE

The purpose of this study was to determine whether the transfer of a marker gene in dual recirculating human placental perfusion is feasible and whether the transgene production is detectable by X-Gal histochemistry.

STUDY DESIGN

Four term human placentas were perfused for 9 to 16 hours in a dual perfusion chamber. At the beginning of each experiment, an adenoviral vector that carried beta-galactosidase gene was added to the maternal perfusate that was entering the intervillous space; at the end, the placental tissues were analyzed for beta-galactosidase activity by X-Gal staining.

RESULTS

Adenovirus-mediated gene transfer resulted in a 0.5% to 1% gene transfer efficiency in placental trophoblastic cells after 9 hours of perfusion, whereas the gene transfer efficiency was much higher, to 5% after 16 hours of perfusion. When postperfusion tissue explant cultures were analyzed for beta-galactosidase expression 56 hours after the perfusion, the transfection rate was as high as 11%.

CONCLUSION

Perfused human placenta can be efficiently transfected with adenoviral vectors, and the expression of the transgene can be detected in the trophoblastic cells. This system can be used for the optimization and analysis of gene transfer conditions to human placenta without any risk to the fetus.

Oxcarbazepine

Oxcarbazepine is one of the recently introduced anti-epileptic drugs (AEDs) in the US. This drug has demonstrated efficacy as adjunctive therapy in adults and children, and as monotherapy in adults for the treatment of seizures of partial onset. There is also convincing evidence of its efficacy in patients with newly diagnosed and refractory trigeminal neuralgia. In addition, the initial efficacy results of oxcarbazepine in other neuropathic pain conditions and in bipolar disorders are encouraging. In this review, recommendations on the optimal clinical use of oxcarbazepine are given based on its pharmacokinetic profile, efficacy and tolerability in those various conditions.

Transplacental transfer and metabolism of buprenorphine

Information on the direct and indirect effects of buprenorphine (BUP) on the fetus is essential for determining its potential for treatment of the pregnant opiate addict. The goal of this investigation is to determine the transplacental transfer of BUP to the fetal circulation, its metabolism, and effects on the tissue. The technique of dual perfusion of placental lobule is used. The range of BUP concentrations investigated included its peak plasma levels (10 ng/ml) in patients under treatment. A biphasic decline in concentration of the drug in the maternal circulation was observed, initially rapid then slow. During the initial (60 min), the tissue sequestered most of BUP resulting in a low (<10%) transplacental transfer of the drug to the fetal circulation. The concentration ratios of the drug in tissue/maternal and tissue/fetal were 13 +/- 6.5 and 27.4 +/- 0.4. The drug sequestered did not have any adverse effects on placental tissue viability and functional parameters. Less than 5% of the perfused BUP was metabolized to norbuprenorphine during the 4 h of perfusion and the metabolite was distributed between the tissue, maternal, and fetal circulations. Taken together, these data suggest that the therapeutic levels of BUP in the maternal circulation may have no indirect effects (via the placenta) on the fetus. The observed low transplacental transfer of BUP to the fetal circuit may explain the moderate/absence of neonatal withdrawal in the limited number of reports on mothers treated with the drug during pregnancy.

Transplacental passage of oxcarbazepine and its metabolites in vivo

PURPOSE

The purpose of this study was to investigate human fetal exposure to oxcarbazepine (OCBZ) in vivo.

METHODS

Transplacental passage and placental tissue concentrations of OCBZ and its metabolites were determined. Maternal venous blood, cord blood, and placental tissue samples from 12 mothers using OCBZ during pregnancy alone or in combination with other antiepileptic drugs were collected. Samples were analyzed with high-performance liquid chromatography.

RESULTS

Maternal venous concentrations of OCBZ and its major metabolites were at same range as cord blood concentrations (OCBZ in maternal serum, 0.19 +/- 0.16 microg/ml, and in cord serum, 0.21 +/- 0.19 microg/ml; 10-hydroxy-10,11-dihydrocarbamazepine (10-OH-CBZ) in maternal serum, 5.69 +/- 2.49 microg/ml, and in cord serum, 5.23 +/- 1.44 microg/ml; 10,11-trans-dihydroxy-10,11-dihydrocarbamazepine (10,11-D) in maternal serum, 0.29 +/- 0.22 microg/ml, and in cord serum, 0.28 +/- 0.14 microg/ml). OCBZ (0.17 +/- 0.16 microg/g placental tissue), 10-OH-CBZ (3.49 +/- 1.34 microg/g placental tissue) and 10,11-D (0.25 +/- 0.11 microg/g placental tissue) were detected in the placental tissue. The amount of OCBZ detected from placental tissue was 0.01% of the daily dose.

CONCLUSIONS

OCBZ, like other antiepileptic drugs, is transferred significantly through the placenta in humans.

Progress report on new antiepileptic drugs: a summary of the Fifth Eilat Conference (EILAT V)

The Fifth Eilat Conference on New Antiepileptic Drugs (AEDs) took place at the Dan Hotel, Eilat, Israel, 25-29 June 2000. Basic scientists, clinical pharmacologists and neurologists from 20 countries attended the conference, whose main themes included recognition of unexpected adverse effects, new indications of AEDs, and patient-tailored AED therapy. According to tradition, the central part of the conference was devoted to a review of AEDs in development, as well to updates on AEDs that have been marketed in recent years. This article summarizes the information presented on drugs in preclinical and clinical development, including AWD 131-138, DP-valproate, harkoseride, LY300164, NPS 1776, NW 1015, pregabalin, remacemide, retigabine, rufinamide and valrocemide. The potential value of an innovative strategy, porcine embryonic GABAergic cell transplants, is also discussed. Finally, updates on felbamate, fosphenytoin, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin, zonisamide, and the antiepileptic vagal stimulator device are presented.

Oxcarbazepine for Treatment of Partial Epilepsy: A Review and Recommendations for Clinical Use

Recent trials and extensive postmarketing use confirm the efficacy and safety of oxcarbazepine (OXC) as a first-line treatment for adults and children with simple partial seizures, complex partial seizures, and partial seizures evolving to secondarily generalized seizures. OXC undergoes reductive metabolism at its keto moiety to form 10-hydroxy-10,11-dihydro-10-oxo-5H-dibenz[b,f]azepine-5-carboxamide (MHD), which is glucuronidated and excreted in the urine, with minimal involvement of the hepatic cytochrome P450-dependent enzymes. OXC has some drug interactions, and does not require titration, allowing for better tolerability. Titration for monotherapy and adjunctive therapy of OXC could begin at 150 mg/day and be increased by 150 mg every 2-3 days until the target dose of 900-1200 mg/day is reached. If necessary, one can go faster and start with up to 600 mg/day and titrate with weekly increments up to 600 mg/day if necessary for seizure control. Conversion to monotherapy can be done overnight or gradually. For gradual conversion, use the recommended titration of OXC and withdraw the baseline antiepileptic drugs gradually by 25%, starting at Day 14 or earlier in case of baseline tolerability issues. Consider reducing the dose of the primary antiepileptic drug during adjunctive therapy in case of adverse events or increase the dose of OXC in case of incomplete seizure control. In children OXC should be started at 8-10 mg/kg/day in two or three divided doses. If clinically indicated the dose can then be increased by 10 mg/kg/day in weekly intervals with final doses up to 30-46 mg/kg/day. Dose adjustment may be necessary in very young children (age 2-5 years) and in patients with renal dysfunction, based on renal clearance. However no adjustment of OXC dose is needed in patients with mild to moderate hepatic dysfunction. OXC has a number of advantages which include rapid titration, no need for safety monitoring (except for uncommon and mostly asymptomatic hyponatremia), a low potential for drug-drug interactions (except for those possibly impairing the effectiveness of oral contraceptives and increasing the serum concentration of phenytoin), a rash rate of less than 5%, similar efficacy and similar or better tolerability and safety compared with first-generation antiepileptic drugs. OXC is a valuable alternative to current treatment options.

Oxcarbazepine

The success of carbamazepine (CBZ) as a broad-spectrum antiepileptic drug (AED) has led to its use as first-line therapy in children and adults for partial and generalized tonic-clonic seizures. The limitations of CBZ include toxicity in sensitive individuals, autoinduction, which requires dose adjustment when therapy is initiated, and chronic hepatic induction, producing drug interactions when CBZ is used with AEDs and other drugs that undergo hepatic metabolism. One of two main products of CBZ microsomal metabolism, CBZ-10,11-epoxide (formed by oxidation of the double bond between C-10 and C-11), appears to provide antiepileptic efficacy but contributes significantly to clinical toxicity. The most common adverse effects of CBZ are central nervous system (CNS) symptoms, followed by gastrointestinal, hepatic, endocrine disturbances, and teratogenic effects. Oxcarbazepine (OXC) was developed to provide a compound chemically similar enough to CBZ to mimic its efficacy and overall safety while improving its side-effect profile. Biotransformation of OXC does not involve formation of an epoxide metabolite. Compared with the parent compound, hepatic microsomal enzyme induction and autoinduction are greatly reduced. The clinical efficacy of OXC compares favorably with CBZ in clinical trials. Clinical development of OXC began in Europe. Results of Phase I trials started to appear in the early 1980s. Controlled clinical trials, reported in the mid- to late 1980s, led to approval of OXC in many European countries, and now in over 50 nations around the world. United States multicenter clinical trials have recently been completed, and at this writing the drug is awaiting approval by the FDA. This article reviews the pharmacology, animal data, outcomes of published controlled clinical trials, postmarketing data, adverse experiences, and current recommendations for clinical use of OXC.

The expression and regulation of drug metabolism in human placenta

The human placenta oxidizes several xenobiotics, although the spectrum of substrates and metabolic activities when compared with the liver appears restricted. Maternal cigarette smoking or PCB exposure increase the expression of CYP1A1. This induced activity is able to catalyze the activation of benzo(a)pyrene into DNA-bound adducts, both in vitro and in vivo. Studies with RT-PCR technique have demonstrated that first trimester placentae express at the mRNA level CYP1A1, 1A2, 2C, 2D6, 2E1, 2F1, 3A4, 3A5, 3A7 and 4B1 and at full term CYP1A1, 2E1, 2F1, 3A3/4, 3A5 and 3A7. However, more detailed studies on cDNA probes or with specific antibodies or 'diagnostic' substrates for other than CYP1A1, 2E1 and 3A gene products have yielded negative results. Studies on human placenta and a chorioncarcinoma cell line, JEG 3 cells, boulster the concept that placental CYP1A1 and 1B1 - although their expression is Ah receptor and ARNT mediated - is controlled by distinct mechanisms. Aromatase, CYP19, and cholesterol side-chain cleaving, CYP11B, genes, proteins and activities are catalytically active in human placentae throughout the pregnancy and those parameters do not seem to be affected by maternal cigarette smoking but rather maternal health status. However, the substrate binding pocket of aromatase accepts as its substrate several xenobiotics and is responsible for constitutive xenobiotic biotransformations.Functional placental glutathione S-transferase, N-acetyl transferase and epoxide hydrolase are expressed via one gene each and their function reflects the placenta as an endocrine organ rather than a xenobiotic-metabolizing unit. However, markers for oxidative stress can be detected in decreased glutathione S-transferase activities.Because human placenta has quite well defined metabolic characteristics, and obtaining placental samples will not meet any drastic ethical difficulties, it could be used more intensively as a source of metabolizing enzymes in in vitro studies during the course of a drug development program. The human placenta, or its subcellular organelles, could serve as a real alternative model for an extrahepatic tissue in replacing recombinant expression systems especially if CYP11, 19, 1A1 or potentially 2E1 are target enzymes for potential metabolic interactions.