Therapeutic Drug Monitoring in Psychiatry: Enhancing Treatment Precision and Patient Outcomes

Psychiatric disorders often require pharmacological interventions to alleviate symptoms and improve quality of life. However, achieving an optimal therapeutic outcome is challenging due to several factors, including variability in the individual response, inter-individual differences in drug metabolism, and drug interactions in polytherapy. Therapeutic drug monitoring (TDM), by measuring drug concentrations in biological samples, represents a valuable tool to address these challenges, by tailoring medication regimens to each individual. This review analyzes the current landscape of TDM in psychiatric practice, highlighting its significance in optimizing drug dosages, minimizing adverse effects, and improving therapeutic efficacy. The metabolism of psychiatric medications (i.e., mood stabilizers, antipsychotics, antidepressants) often exhibits significant inter-patient variability. TDM can help address this variability by enhancing treatment personalization, facilitating early suboptimal- or toxic-level detection, and allowing for timely interventions to prevent treatment failure or adverse effects. Furthermore, this review briefly discusses technological advancements and analytical methods supporting the implementation of TDM in psychiatric settings. These innovations enable quick and cost-effective drug concentration measurements, fostering the widespread adoption of TDM as a routine practice in psychiatric care. In conclusion, the integration of TDM in psychiatry can improve treatment outcomes by individualizing medication regimens within the so-called precision medicine.

Pharmacogenetics and Oxcarbazepine in Children and Adolescents: Beyond HLA-B*15:02

Background: Oxcarbazepine is thought to be better-tolerated and less susceptible to drug-drug interactions than its predecessor, carbamazepine. Genetic testing for HLA-B*15:02 is recommended in specific populations to identify those at high risk of severe hypersensitivity reactions; however, other pharmacologic and pharmacogenetic factors that can impact drug disposition may be involved. Methods: We present a case of an 8-year-old boy treated with oxcarbazepine who developed drug reaction with eosinophilia and systemic symptoms (DRESS) with Stevens-Johnsons syndrome overlap and was negative for HLA-B*15:02. We review the extant literature related to oxcarbazepine disposition, and potential pharmacogenetic variants in aldoketoreductase 1C (AKR1C)2-4 that may contribute to this risk. Results: Genetic variability in oxcarbazepine disposition pathways may contribute to tolerability and toxicity, including the development of hypersensitivity reactions. Conclusions: While preemptive genetic testing for HLA-B*15:02 in individuals of Asian ancestry is recommended to prevent severe hypersensitivity reactions to oxcarbazepine, oxcarbazepine concentrations and AKR1C variation may contribute to the risk of severe adverse reactions. We provide recommendations for future study to elucidate whether these individual factors are important for reducing the risk of severe adverse events.

Simple HPLC-UV Method for Therapeutic Drug Monitoring of 12 Antiepileptic Drugs and Their Main Metabolites in Human Plasma

The objective of the present report was to develop and validate a simple, selective, and reproducible high-performance liquid chromatography method with UV detection suitable for routine therapeutic drug monitoring of the most commonly used antiepileptic drugs and some of their metabolites. Simple precipitation of plasma proteins with acetonitrile was used for sample preparation. 10,11-dihydrocarbamazepine was used as an internal standard. Chromatographic separation of the analytes was achieved by gradient elution on a Phenyl-Hexyl column at 40 °C, using methanol and potassium phosphate buffer (25 mM; pH 5.1) as a mobile phase. The method was validated according to the FDA guidelines for bioanalytical method validation. It showed to be selective, accurate, precise, and linear over the concentration ranges of 1-50 mg/L for phenobarbital, phenytoin, levetiracetam, rufinamide, zonisamide, and lacosamide; 0.5-50 mg/L for lamotrigine, primidone, carbamazepine and 10-monohydroxycarbazepine; 0.2-10 mg/L for carbamazepine metabolites: 10,11-trans-dihydroxy-10,11-dihydrocarbamazepine and carbamazepine-10,11-epoxide; 0.1-10 mg/L for oxcarbazepine; 2-100 mg/L for felbamate and 3-150 mg/L for ethosuximide. The suitability of the validated method for routine therapeutic drug monitoring was confirmed by quantification of the analytes in plasma samples from patients with epilepsy on combination antiepileptic therapy.

Effect of Penetration Enhancers on Transdermal Delivery of Oxcarbazepine, an Antiepileptic Drug Using Microemulsions

Oxcarbazepine (OXC) is an anticonvulsant drug, indicated for the treatment of the neurological disorder, epilepsy. The objective of the present study was to evaluate the transdermal delivery of OXC from microemulsions using different penetration enhancers. Transcutol® P (TRC), oleic acid (OA), cineole (cin), Labrasol (LS), Tween 80 (T80) and N-Methyl-Pyrrolidone (NMP) were used as penetration enhancers as well as microemulsion components. Simple formulations of OXC in propylene glycol (PG) incorporating various penetration enhancers and combination of penetration enhancers were also evaluated for transdermal delivery. Drug delivery and penetration enhancement were studied using human cadaver skin on Franz diffusion cells. The results showed that all penetration enhancers improved the rate of permeation of OXC compared to the control. The flux of drug delivery from the various formulations was found to be, in decreasing order, cin > OA + TRC > NMP > TRC > OA. Overall, microemulsions prepared using cineole, Tween 80 and Transcutol® P (TRC) were shown to be provide the best penetration enhancement for OXC.

Physiologically-based pharmacokinetic modeling of oxcarbazepine and levetiracetam during adjunctive antiepileptic therapy in children and adolescents

Oxcarbazepine (OXZ) and levetiracetam (LEV) are two new generation anti‐epileptic drugs, often co‐administered in children with enzyme‐inducing antiepileptic drugs (EIAEDs). The anti‐epileptic effect of OXZ and LEV are linked to the exposure of OXZ’s active metabolite 10‐monohydroxy derivative (MHD) and (the parent) LEV, respectively. However, little is known about the confounding effect of age and EIAEDs on the pharmacokinetics (PKs) of MHD and LEV. To address this knowledge gap, physiologically‐based pharmacokinetic (PBPK) modeling was performed in the PK‐Sim software using literature data from children greater than or equal to 2 years of age. Age‐related changes in clearance (CL) of MHD and LEV were characterized, both in the presence (group 1) and absence (group 2) of concomitant EIAEDs. The drug‐drug interaction effect of EIAEDs was estimated as the difference in CL estimates between groups 1 and 2. PBPK modeling suggests that bodyweight normalized CL (ml/min/kg) is higher in younger children than their older counterparts (i.e., due to an influence of age). Concomitant EIAEDs further increase MHD’s CL to a fixed extent of 25% at any age, but EIAEDs’ effect on LEV’s CL increases with age from 20% (at 2 years) to 30% (at adolescence). Simulations with the maximum recommended doses (MRDs) revealed that children between 2 and 4 years and greater than 4 years, who are not on EIAEDs, are at risk of exceeding the reference exposure range for OXZ and LEV, respectively. This analysis demonstrates the use of PBPK modeling in understanding the confounding effect of age and comedications on PKs in children and adolescents.

Population pharmacokinetics of oxcarbazepine: a systematic review

INTRODUCTION

Oxcarbazepine is commonly used as first-line treatment for partial and generalized tonic-clonic seizures. Owing to the high pharmacokinetic variability, several population pharmacokinetic models have been developed for oxcarbazepine to explore potential covariates that affect its pharmacokinetic variation.

AREAS COVERED

This review summarizes the published population pharmacokinetic studies of oxcarbazepine in children and adults available in PubMed and Embase databases. The quality of the retrieved studies was evaluated, and significant covariates that may have an impact on the dosage regimen of oxcarbazepine were explored.

EXPERT OPINION

The pharmacokinetics of oxcarbazepine was founded to be affected by body weight and co-administration with enzyme inducers. Pediatric patients require a higher dose per kilogram than adults because children generally have a higher clearance than adults. Moreover, to maintain the target concentration, patients co-administrate with enzyme inducers need a higher dose than monotherapy due to higher clearance in those patients. Because limited information is available for exposure-response relationship, additional pharmacokinetic/pharmacodynamics investigations of oxcarbazepine need to be conducted to optimize the dosage regimen in clinical practice.

Distinct effects on cAMP signaling of carbamazepine and its structural derivatives do not correlate with their clinical efficacy in epilepsy

The antiepileptic sodium channel blocker, carbamazepine, has long been known to be able to attenuate cAMP signals. This could be of clinical importance since cAMP signaling has been shown to be involved in epileptogenesis and seizures. However, no information on the ability to affect cAMP signaling is available for the marketed structural derivatives, oxcarbazepine and eslicarbazepine acetate or their dominating metabolite, licarbazepine. Thus, we employed a HEK293 cell line stably expressing a cAMP biosensor to assess the effect of these two drugs on cAMP accumulation. We find that oxcarbazepine does not affect cAMP accumulation whereas eslicarbazepine acetate, surprisingly, is able to enhance cAMP accumulation. Since the transcription of ADCY8 (adenylyl cyclase isoform 8; AC8) has been found to be elevated in epileptic tissue from patients, we subsequently expressed AC8 in the HEK293 cells. In the AC8-expressing cells, oxcarbazepine was now able to attenuate whereas eslicarbazepine maintained its ability to increase cAMP accumulation. However, at all concentrations tested, licarbazepine demonstrated no effect on cAMP accumulation. Thus, we conclude that the effects exerted by carbamazepine and its derivatives on cAMP accumulation do not correlate with their clinical efficacy in epilepsy. However, this does not disqualify cAMP signaling per se as a potential disease-modifying drug target for epilepsy since more potent and selective inhibitors may be of therapeutic value.

Comparison of oxcarbazepine efficacy and MHD concentrations relative to age and BMI: Associations among ABCB1, ABCC2, UGT2B7, and SCN2A polymorphisms

Genetic polymorphisms are related to the concentration and efficacy of oxcarbazepine (OXC). 10-Hydroxycarbazepine (MHD) is the major pharmacologically active metabolite of OXC, and it exerts an antiepileptic effect. This study aimed to explore the connection between the MHD concentration and genes such as ATP-binding cassette B1 (ABCB1), ATP-binding cassette C2 (ABCC2), UDP-glucuronosyltransferase-2B7 and sodium voltage-gated channel alpha subunit 2 (SCN2A), which participate in the antiepileptic function of OXC.Total 218 Chinese epileptic patients, were stratified into different groups according to their age, body mass index (BMI) and OXC efficacy. The genotypes of 7 single nucleotide polymorphisms in all subjects were determined by polymerase chain reaction-improved multiple ligase detection reaction assay. The MHD plasma concentration was detected by high-performance liquid chromatography and then standardized through dosage and body weight.In general, the ABCC2 rs2273697 mutant (P = .026) required a significantly higher standardized MHD concentration. For age groups, carriers of the ABCC2 rs2273697 mutant showed a significantly higher standardized MHD concentration than noncarriers in the juvenile group (P = .033). In terms of BMI, a significantly higher standardized MHD concentration was found in the ABCB1 rs2032582 mutant of the normal weight group (P = .026). The SCN2A rs17183814 mutant required a significantly higher OXC maintenance (P = .014) in the low-weight group, while lower OXC maintenance dose (P = .044) and higher standardized MHD concentration (P = .007) in the overweight group.The ABCC2 rs2273697 polymorphism was significantly associated with MHD plasma concentration in the whole patient cohort and in patients stratified by different ages, this finding provides potential theoretical guidance for the rational and safe clinical use of OXC.

Revolutionizing Therapeutic Drug Monitoring with the Use of Interstitial Fluid and Microneedles Technology

While therapeutic drug monitoring (TDM) that uses blood as the biological matrix is the traditional gold standard, this practice may be impossible, impractical, or unethical for some patient populations (e.g., elderly, pediatric, anemic) and those with fragile veins. In the context of finding an alternative biological matrix for TDM, this manuscript will provide a qualitative review on: (1) the principles of TDM; (2) alternative matrices for TDM; (3) current evidence supporting the use of interstitial fluid (ISF) for TDM in clinical models; (4) the use of microneedle technologies, which is potentially minimally invasive and pain-free, for the collection of ISF; and (5) future directions. The current state of knowledge on the use of ISF for TDM in humans is still limited. A thorough literature review indicates that only a few drug classes have been investigated (i.e., anti-infectives, anticonvulsants, and miscellaneous other agents). Studies have successfully demonstrated techniques for ISF extraction from the skin but have failed to demonstrate commercial feasibility of ISF extraction followed by analysis of its content outside the ISF-collecting microneedle device. In contrast, microneedle-integrated biosensors built to extract ISF and perform the biomolecule analysis on-device, with a key feature of not needing to transfer ISF to a separate instrument, have yielded promising results that need to be validated in pre-clinical and clinical studies. The most promising applications for microneedle-integrated biosensors is continuous monitoring of biomolecules from the skin's ISF. Conducting TDM using ISF is at the stage where its clinical utility should be investigated. Based on the advancements described in the current review, the immediate future direction for this area of research is to establish the suitability of using ISF for TDM in human models for drugs that have been found suitable in pre-clinical experiments.

Population pharmacokinetics of oxcarbazepine and its monohydroxy derivative in epileptic children

AIMS

Oxcarbazepine is an antiepileptic drug with an activity mostly due to its monohydroxy derivative metabolite (MHD). A parent-metabolite population pharmacokinetic model in children was developed to evaluate the consistency between the recommended paediatric doses and the reference range for trough concentration (C_trough ) of MHD (3-35 mg l^-1 ).

METHODS

A total of 279 plasma samples were obtained from 31 epileptic children (age 2-12 years) after a single dose of oxcarbazepine. Concentration-time data were analysed with Monolix 4.3.2. The probability to obtain C_trough between 3-35 mg l^-1 was determined by Monte Carlo simulations for doses ranging from 10 to 90 mg kg^-1  day^-1 .

RESULTS

A parent-metabolite model with two compartments for oxcarbazepine and one compartment for MHD best described the data. Typical values for oxcarbazepine clearance, central and peripheral distribution volume and distribution clearance were 140 l h^-1  70 kg^-1 , 337 l 70 kg^-1 , 60.7 l and 62.5 l h^-1 , respectively. Typical values for MHD clearance and distribution volume were 4.11 l h^-1  70 kg^-1 and 54.8 l 70 kg^-1 respectively. Clearances and distribution volumes of oxcarbazepine and MHD were related to body weight via empirical allometric models. Enzyme-inducing antiepileptic drugs (EIAEDs) increased MHD clearance by 29.3%. Fifty-kg children without EIAEDs may need 20-30 mg kg^-1  day^-1 instead of the recommended target maintenance dose (30-45 mg kg^-1  day^-1 ) to obtain C_trough within the reference range. By contrast, 10-kg children with EIAEDs would need 90 mg kg^-1  day^-1 instead of the maximum recommended dose of 60 mg kg^-1  day^-1 .

CONCLUSION

This population pharmacokinetic model of oxcarbazepine supports current dose recommendations, except for 10-kg children with concomitant EIAEDs and 50-kg children without EIAEDs.

Evaluation of cytochrome P450 inductions by anti-epileptic drug oxcarbazepine, 10-hydroxyoxcarbazepine, and carbamazepine using human hepatocytes and HepaRG cells

Anti-epileptic drug oxcarbazepine is structurally related to carbamazepine, but has reportedly different metabolic pathway. Auto-induction potentials of oxcarbazepine, its pharmacologically active metabolite 10-hydroxyoxcarbazepine and carbamazepine were evaluated by cytochrome P450 (CYP) 1A2, CYP2B6 and CYP3A4 mRNA levels and primary metabolic rates using human hepatocytes and HepaRG cells. For the CYP1A2 the induction potential determined as the fold change in mRNA levels was 7.2 (range: 2.3-11.5) and 10.0 (6.2-13.7) for oxcarbazepine and carbamazepine, respectively, while 10-hydroxyoxcarbazepine did not induce. The fold change in mRNA levels for CYP2B6 was 11.5 (3.2-19.3), 7.0 (2.5-10.8) and 14.8 (3.1-29.1) for oxcarbazepine, 10-hydroxyoxcarbazepine and carbamazepine, respectively. The fold change for CYP3A4 induction level by oxcarbazepine, 10-hydroxyoxcarbazepine and carbamazepine was 3.5 (1.2-7.4), 2.7 (0.8-5.7) and 8.3 (3.5-14.5), respectively. The data suggest lower induction potential of oxcarbazepine and 10-hydroxyoxcarbazepine relative to carbamazepine. The results in HepaRG cells showed similar trend as the human hepatocytes. After incubation for 72 h in hepatocytes and HepaRG cells, auto-induction was evident for only carbamazepine metabolism. The 10-keto group instead of double bond at C10 position is evidently a determinant factor for limited auto-induction of P450 enzymes by oxcarbazepine.

Population pharmacokinetics modeling of oxcarbazepine to characterize drug interactions in Chinese children with epilepsy

AIM

To develop a population pharmacokinetics model of oxcarbazepine in Chinese pediatric patients with epilepsy, and to study the interactions between oxcarbazepine and other antiepileptic drugs (AEDs).

METHODS

A total of 688 patients with epilepsy aged 2 months to 18 years were divided into model (n=573) and valid (n=115) groups. Serum concentrations of the main active metabolite of oxcarbazepine, 10-hydroxycarbazepine (MHD), were determined 0.5-48 h after the last dosage. A population pharmacokinetics (PPK) model was constructed using NLME software. This model was internally evaluated using Bootstrapping and goodness-of-fit plots inspection. The data of the valid group were used to calculate the mean prediction error (MPE), mean absolute prediction error (MAE), mean squared prediction error (MSE) and the 95% confidence intervals (95% CI) to externally evaluate the model.

RESULTS

The population values of pharmacokinetic parameters estimated in the final model were as follows: Ka=0.83 h-1, Vd=0.67 L/kg, and CL=0.035 L·kg(-1)·h(-1). The enzyme-inducing AEDs (carbamazepine, phenytoin, phenobarbital) and newer generation AEDs (levetiracetam, lamotrigine, topiramate) increased the weight-normalized CL value of MHD by 17.4% and 10.5%, respectively, whereas the enzyme-inhibiting AED valproic acid decreased it by 3%. No significant association was found between the CL value of MHD and the other covariates. For the final model, the evaluation results (95% CI) were MPE=0.01 (-0.07-0.10) mg/L, MAE=0.46 (0.40-0.51) mg/L, MSE=0.39 (0.27-0.51) (mg/L)(2).

CONCLUSION

A PPK model of OXC in Chinese pediatric patients with epilepsy is established. The enzyme-inducing AEDs and some newer generation AEDs (lamotrigine, topiramate) could slightly increase the metabolism of MHD.

Therapeutic drug monitoring in the neurocritical care unit

PURPOSE OF REVIEW

Various antiepileptics, sedative and anesthetic agents are used in the neurocritical care setting and therapeutic drug monitoring (TDM) has been proposed as a means to individualize dosing to ensure efficacy, avoid toxicity, and to account for drug-drug interactions. The purpose of this review is to highlight key articles relating to TDM published in the last 5 years with a focus on drug therapy for seizures, status epilepticus, and traumatic brain injury.

RECENT FINDINGS

Current evidence supports TDM of first-generation antiepileptics, and free-level monitoring for phenytoin and valproic acid is recommended in the neurocritical care population. There are insufficient data to recommend routine TDM of second-generation antiepileptics at this time. In traumatic brain injury, routine TDM of barbiturate infusions appears to be of little value in guiding or evaluating patient response to therapy except to differentiate between drug-induced coma and brain death. Although TDM of sedative agents has been studied, the use of clinical sedation scales is preferred over TDM in evaluating a patient's level of sedation.

SUMMARY

Therapeutic drug monitoring plays an important role in the care of patients in the neurocritical care setting but is applicable only to a limited number of drugs.

Drug interaction and pharmacokinetic modeling of oxcarbazepine in korean patients with epilepsy

OBJECTIVES

To determine first whether there was a clear relationship between concentrations of the active metabolite of oxcarbazepine (OXC), 10-hydroxycarbamazepine (OHC), and dose adjusted for weight, and second, whether the clearance of OHC was influenced by comedication with enzyme-inducing antiepileptic drugs (EIAED).

METHODS

We analyzed 254 cases (patients 3-80 years of age) of OXC therapeutic drug monitoring, retrospectively. The cases were categorized into OXC monotherapy (n = 78), OXC in combination with EIAED (n = 73), and OXC in combination with non-EIAED (n = 103). The serum OHC concentrations of predose samples were measured by high-performance liquid chromatography. A population pharmacokinetic model was developed using NONMEM.

RESULTS

The mean ± SD serum concentration of OHC was 14.47 ± 8.28 μg/mL at a mean daily dose of 16.22 ± 7.99 mg/kg. The serum concentration of OHC was correlated with the OXC dose per body weight (r = 0.6005; P < 0.0001). No association was found between OHC concentration and patient age, weight, sex, or seizure type. The concentration-to-dose ratio on OXC in combination with EIAED was significantly lower than that on OXC monotherapy (P = 0.002) or OXC in combination with non-EIAED (P < 0.0001). In population pharmacokinetic modeling, the apparent clearance of OHC was higher by 31.2% in combination with EIAED than in other groups.

CONCLUSIONS

The serum concentration of OHC was statistically significantly correlated with the dose of OXC and negatively correlated with comedication of EIAED. Population pharmacokinetic analysis showed that the apparent clearance of OHC increased with comedication with EIAEDs.

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

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

[Therapeutic drug monitoring of oxcarbazepine]

Oxcarbazepine is an analogue of carbamazepine, used for the treatment of partial seizure with or without secondary generalization. The two forms R and S of the mono-hydroxylated derivatives (MHD) are responsible for most of the anti-convulsant activity and it is the concentrations of MHD that are relevant in therapeutic drug monitoring (TDM). Analysis of currently literature provides no well-established relationship between plasma concentration of MHD and efficiency or toxicity. Although there is not a validated therapeutic range, the residual concentrations of usually observed therapeutic MHD are situated between 12 and 30 mg/L. In certain pathological or physiological circumstances, the pharmacokinetic variability of the oxcarbazepine can be considerable, but this strong unpredictability does not nevertheless justify the TDM of the MHD. Based on the available evidence, TDM of MHD is not routinely warranted but may be possibly useful in specific situations such as pregnancy or renal insufficiency.