Sources of lamotrigine pharmacokinetic variability: A systematic review of population pharmacokinetic analyses

Population Pharmacokinetics of Lamotrigine and Its N2-Glucuronide Metabolite in Chinese Patients With Epilepsy

BACKGROUND

Lamotrigine is a new antiepileptic drug with substantial interindividual variability in its pharmacokinetics and therapeutic responses. This study aimed to develop population pharmacokinetic (PPK) models of lamotrigine and its N2-glucuronide metabolites for model-informed individualized therapy.

METHODS

A total of 353 plasma concentrations from Chinese patients with epilepsy receiving oral lamotrigine were used to develop a population PPK model using a nonlinear mixed effects modeling method. One- and two-compartment models were applied to the nonmetabolite and metabolite model, respectively. Forward addition and backward elimination were used to establish the final model. Model validation was performed using standard goodness-of-fit, bootstrap, visual predictive checks, and normalized prediction distribution errors. Finally, simulations were performed to propose lamotrigine dosages in different situations to achieve trough concentrations within the reference interval (2.5-15 mg/L).

RESULTS

For both final population PPK models, coadministration with valproic acid (VPA) or enzyme inducer, and body weight significantly affected lamotrigine clearance. The final models for lamotrigine clearance were and for nonmetabolite and metabolite models, respectively. The precision of the PPK parameters was acceptable, and the models exhibited good predictability. Monte Carlo simulations revealed that the lamotrigine dosage administered to patients combined with an enzyme inducer must be tripled that administered with VPA to reach the target trough concentration.

CONCLUSIONS

Variability in the pharmacokinetics of lamotrigine is large. Coadministration of VPA or an enzyme inducer and body weight are the most important factors in lamotrigine clearance in Chinese patients with epilepsy. The developed population PPK models might support further optimization of lamotrigine dosing regimens.

Breast cancer resistance protein polymorphism ABCG2 c.421C>A (rs2231142) moderates the effect of valproate on lamotrigine trough concentrations in adults with epilepsy

BACKGROUND

Valproate inhibits clearance of lamotrigine and greatly increases its concentrations. We assessed whether this effect was moderated by a polymorphism (ABCG2 c.421C>A) of the breast cancer resistance protein.

METHODS

In two consecutive independent studies in adults with epilepsy on lamotrigine monotherapy or cotreated with valproate: (i) Exposure to valproate was considered treatment, (ii) dose-adjusted lamotrigine troughs at steady state were the outcome, and (iii) ABCG2 c.421C>A genotype (wild-type [wt] homozygosity or variant carriage) was the tested moderator. We used entropy balancing (primary analysis) and exact/optimal full matching (secondary analysis) to control for confounding, including polymorphisms (and linked polymorphisms) suggested to affect exposure to lamotrigine (UGT1A4*3 c.142T>G, rs2011425; UGT2B7-161C>T, rs7668258; ABCB1 1236C>T, rs1128503) to generate frequentist and Bayesian estimates of valproate effects (geometric means ratios [GMR]).

RESULTS

The two studies yielded consistent results (replicated); hence, we analyzed combined data (total N = 471, 140 treated, 331 controls, 378 ABCG2 c.421C>A wt subjects, 93 variant carriers). Primary analysis: in variant carriers, valproate effect (GMR) on lamotrigine (treated, n = 21 vs. controls, n = 72) was around 60% higher than in wt subjects (treated, n = 119 vs. controls, n = 259)-ratio of GMRs 1.61 (95%CI 1.23-2.11) (frequentist) and 1.63 (95%CrI 1.26-2.10) (Bayes). Similar differences in valproate effects between variant carriers and wt subjects were found in the secondary analysis (valproate troughs up to 364 μmol/L vs. no valproate; or valproate ≥364 μmol/L vs. no valproate). Susceptibility of the estimates to unmeasured confounding was low.

CONCLUSION

Data suggest that polymorphism rs2231142 moderates the effect of valproate on exposure to lamotrigine.

Bearing variant alleles at uridine glucuronosyltransferase polymorphisms UGT2B7 -161C > T (rs7668258) or UGT1A4*3 c.142 T > G (rs2011425) has no relevant consequences for lamotrigine troughs in adults with epilepsy

PURPOSE

To estimate whether epilepsy patients with variant UGT2B7 -161C > T (rs7668258) or UGT1A4*3 c.142 T > G (rs2011425) alleles differ from their wild-type (wt) peers in exposure to lamotrigine.

METHODS

Consecutive adults on lamotrigine monotherapy or lamotrigine + valproate co-treatment undergoing routine therapeutic drug monitoring, otherwise generally healthy and free of interacting drugs, were genotyped for UGT2B7 -161C > T and UGT1A4*3 c.142 T > G. Heterozygous, variant homozygous, or combined heterozygous/variant homozygous subjects were compared to their wt controls for dose-adjusted lamotrigine troughs with adjustment for age, sex, body weight, rs7668258/rs2011425, polymorphisms of efflux transporter proteins ABCG2 c.421C > A (rs2231142) and ABCB1 1236C > T (rs1128503), and level of exposure to valproate using covariate entropy balancing.

RESULTS

Of the 471 included patients, 328 (69.6%) were on monotherapy and 143 were co-treated with valproate. Dose-adjusted lamotrigine troughs in UGT2B7 -161C > T heterozygous (CT, n = 237) or variant homozygous (TT, n = 115) subjects were closely similar to those in their wt controls (CC, n = 119): geometric means ratios (GMRs) (frequentist and Bayes) 1.00 (95%CI 0.86-1.16) and 1.00 (95%CrI 0.83-1.22) for CT vs. CC; and 0.97 (0.81-1.17) and 0.97 (0.80-1.20) for TT vs. CC subjects. Lamotrigine troughs were also closely similar in UGT1A4*3 c.142 T > G variant carriers (n = 106: 102 TG + 4 GG subjects) and wt controls (TT, n = 365): GMR = 0.95 (0.81-1.12) frequentist, 0.96 (0.80-1.16) Bayes. GMRs for variant carriers vs. wt controls were around unity also at different levels of exposure to valproate.

CONCLUSION

Dose-adjusted lamotrigine troughs in epilepsy patients with variant UGT2B7 -161C > T or UGT1A4*3 c.142 T > G alleles are equivalent to those in their respective wt peers.

A novel approach for pharmacological substantiation of safety signals using plasma concentrations of medication and administrative/healthcare databases: a case study using Danish registries for an FDA warning on lamotrigine

PHARMACOM-EPI is a novel framework to predict plasma concentrations of drugs at the time of occurrence of clinical outcomes. In early 2021, the U.S. Food and Drug Administration (FDA) issued a warning on the antiseizure drug lamotrigine claiming that it has the potential to increase the risk of arrhythmias and related sudden cardiac death due to a pharmacological sodium channel-blocking effect. We hypothesized that the risk of arrhythmias and related death is due to toxicity. We used the PHARMACOM-EPI framework to investigate the relationship between lamotrigine's plasma concentrations and the risk of death in older patients using real-world data. Danish nationwide administrative and healthcare registers were used as data sources and individuals aged 65 years or older during the period 1996 - 2018 were included in the study. According to the PHARMACOM-EPI framework, plasma concentrations of lamotrigine were predicted at the time of death and patients were categorized into non-toxic and toxic groups based on the therapeutic range of lamotrigine (3-15mg/L). Over 1 year of treatment, the incidence rate ratio (IRR) of all-cause mortality was calculated between the propensities score matched toxic and non-toxic groups. In total, 7286 individuals were diagnosed with epilepsy and were exposed to lamotrigine, 432 of which had at least one plasma concentration measurement The pharmacometric model by Chavez et al. was used to predict lamotrigine's plasma concentrations considering the lowest absolute percentage error among identified models (14.25%, 95% CI: 11.68-16.23). The majority of lamotrigine associated deaths were cardiovascular-related and occurred among individuals with plasma concentrations in the toxic range. The IRR of mortality between the toxic group and non-toxic group was 3.37 [95% CI: 1.44-8.32] and the cumulative incidence of all-cause mortality exponentially increased in the toxic range. Application of our novel framework PHARMACOM-EPI provided strong evidence to support our hypothesis that the increased risk of all-cause and cardiovascular death was associated with a toxic plasma concentration level of lamotrigine among older lamotrigine users.

Understanding Lamotrigine's Role in the CNS and Possible Future Evolution

The anti-epileptic drug lamotrigine (LTG) has been widely used to treat various neurological disorders, including epilepsy and bipolar disorder. However, its precise mechanism of action in the central nervous system (CNS) still needs to be determined. Recent studies have highlighted the involvement of LTG in modulating the activity of voltage-gated ion channels, particularly those related to the inhibition of neuronal excitability. Additionally, LTG has been found to have neuroprotective effects, potentially through the inhibition of glutamate release and the enhancement of GABAergic neurotransmission. LTG's unique mechanism of action compared to other anti-epileptic drugs has led to the investigation of its use in treating other CNS disorders, such as neuropathic pain, PTSD, and major depressive disorder. Furthermore, the drug has been combined with other anti-epileptic drugs and mood stabilizers, which may enhance its therapeutic effects. In conclusion, LTG's potential to modulate multiple neurotransmitters and ion channels in the CNS makes it a promising drug for treating various neurological disorders. As our understanding of its mechanism of action in the CNS continues to evolve, the potential for the drug to be used in new indications will also be explored.

Simultaneous determination of plasma lamotrigine, lamotrigine N2-glucuronide and lamotrigine N2-oxide by UHPLC-MS/MS in epileptic patients

The plasma concentration of lamotrigine (LTG) and its metabolites has great interindividual variability. An UHPLC-MS/MS method for simultaneous determination of LTG and lamotrigine N2-glucuronide (LTG N2-GLUC), lamotrigine N2-oxide was developed, validated, and applied in 58 plasma samples. The ion transition was m/z 256.0 > 144.9 for LTG, 432.1 > 256.0 for LTG N2-GLUC, 272.2 > 241.9 for LTG N2-oxide, and 259.1 > 144.8 for LTG-¹³C₃ (internal standard). The flow rate was 0.4 mL/min with a run time of 3 min. The calibration range was 0.025-2 mg/L for LTG and LTG N2-GLUC, and 0.000625-0.05 mg/L for LTG N2-oxide. For all analytes, the intra-day and inter-day bias and imprecision were -11.7-5.7 % and less than 14.3 %, and the internal standard normalized recovery and matrix factor were 91.7-101.5 % and 98.1-110.1 % with CV < 13. 7%. Ten- and twenty-fold dilution with blank plasma did not affect the analysis. All analytes were stable in plasma at room temperature for 8 h, at -80 °C for 80 days, and after 3 freeze-thaw cycles. The LTG N2-GLUC/LTG ratio was 0.44 in LTG monotherapy group. The ratio was reduced to 0.17 when co-administrated with valproic acid, while elevated to 0.82 when co-administrated with enzyme inducer. In conclusion, this method is suitable for simultaneous determination of LTG, LTG N2-GLUC and LTG N2-oxide in human plasma.

Magnitude of Lamotrigine Exposure Through Breastfeeding

Importance: Lamotrigine use during breastfeeding has significantly increased in the recent years, whereas breast milk lamotrigine pharmacokinetics data are still sparse. Objectives: To assess lamotrigine exposure in breastfed infants by monitoring maternal serum and breast milk concentrations. Methods: Breastfeeding women treated with lamotrigine were recruited to this study. Maternal trough breast milk and serum samples were collected, and additional breast milk samples were collected 1, 3, 6, 9, 12 hours after lamotrigine consumption. Trough breast milk/serum ratios (M/S ratio) and breast milk area under the curve (AUC) values were calculated. Results: Twenty-one breastfeeding women were recruited to this study, and the final dataset was based on the samples collected from 17 women. Lamotrigine trough serum and mother's milk concentrations were 5.1 ± 3.3 mg/L and 3.1 ± 1.9 mg/L, respectively (mean ± standard deviation). The trough M/S ratio of lamotrigine was 0.66 ± 0.22. The lamotrigine breast milk average AUC was 41.7 ± 24.6 mg·h/L. The estimated infant dose of lamotrigine was 0.52 ± 0.31 mg/kg/day and 0.26 ± 0.15 mg/kg/day for fully and partially breastfed infants, respectively. Significant correlation was found between the maternal lamotrigine serum trough concentrations and the breast milk parameters: trough breast milk concentrations (Spearman's rho = 0.986, p < 0.0001) and breast milk AUC values (Spearman's rho = 0.941, p < 0.0001). No significant correlation was found between the maternal lamotrigine daily dose and serum trough concentrations, breast milk trough concentrations, and breast milk AUC values (Spearman's rho = 0.294, 0.285, and 0.438, p = 0.252, 0.396, and 0.078, respectively). Conclusion and Relevance: High correlation between the maternal lamotrigine trough serum concentrations and the breast milk AUC values was found, implying that monitoring the maternal lamotrigine serum concentrations can be useful for prediction of exposure of infants to lamotrigine through the breast milk. The trial was registered in the Israeli trials registry MOH_2021-09-05_010243 at September 5, 2021 Retrospectively registered https://my.health.gov.il/CliniTrials.

Factors influencing methotrexate and methotrexate polyglutamate in patients with rheumatoid arthritis: a systematic review of population pharmacokinetics

Low dose methotrexate (MTX) is commonly used in the treatment of rheumatoid arthritis. The clinical effect is mediated by its metabolite, methotrexate polyglutamate (MTX-PGn). The drug exhibits high interindividual pharmacokinetic variability and the optimal MTX dose is different among individuals. Thus, several MTX population pharmacokinetic (PopPK) models were developed to characterize factors affecting MTX pharmacokinetic variability. This review summarizes significant predictors for MTX pharmacokinetics and identifies knowledge gaps to be further examined. A total of 359 articles were identified from a systematic search of four databases: PubMed, Science Direct, and CINAHL Complete. Of these eight studies were included. Most studies investigated influential factors on MTX pharmacokinetics, but information on MTX-PGn is limited, with only one study performing a parent-metabolite (MTX-PG3) model. MTX pharmacokinetics was described using a two-compartment model with first-order elimination in most studies, with the MTX clearance ranging from 6.94 to 12.39 L/h. Significant predictors influencing MTX clearance included weight, creatinine clearance, sex, OATP1B3 polymorphism, and MTX multiple dosing. While body mass index and red blood cell counts were significant predictors for MTX-PG3 clearance. Providing that MTX-PGn plays a crucial role in clinical effect, further studies should determine other factors affecting MTX-PGn as well as its relationship with clinical response.

Managing the Unpredictable: Mechanistic Analysis and Clinical Recommendations for Lamotrigine Treatment after Bariatric Surgery

Bariatric surgery may alter the absorption and overall bioavailability of oral drugs. Lamotrigine is a major antiepileptic and mood stabilizer, that its use after bariatric surgery has not yet been studied. In this article, we provide a thorough mechanistic analysis of the effects of bariatric surgery on multiple mechanisms important for the absorption, bioavailability and overall pharmacokinetics of lamotrigine. Attributable to its pharmacokinetic properties and drug characteristics, the use of lamotrigine after bariatric surgery may be challenging. The complex situation in which some mechanisms may lead to increased drug exposure (e.g., decreased metabolism, weight loss) while others to its decrease (e.g., hampered dissolution/solubility, decreased gastric volume), may result in lowered, unchanged, or enhanced lamotrigine plasma levels after the surgery. We conclude with a set of clinical recommendations for lamotrigine treatment after bariatric surgery, aiming to allow better patient care, and emphasizing the extra caution that needs to be taken with these patients.

Predictive Performance of Published Tacrolimus Population Pharmacokinetic Models in Thai Kidney Transplant Patients

BACKGROUND AND OBJECTIVE

Tacrolimus is a narrow therapeutic index drug with high pharmacokinetic variability, and several tacrolimus population pharmacokinetic (PopPK) models were developed to guide individualized drug dosing. These models, however, may not perform well in other clinical settings. Therefore, we aimed to assess the predictive ability of published tacrolimus PopPK models using a dataset of Thai kidney transplant patients.

METHODS

The external dataset was retrospectively collected from medical records of Bhumibol Adulyadej Hospital, Thailand. Published tacrolimus PopPK models were systematically searched from PubMed, Science Direct, CINAHL Complete, and Scopus databases. Models conducted using a nonlinear mixed-effects approach with covariate resemblance to our external dataset were selected. The external dataset consisted of Thai kidney transplant patients receiving oral immediate- or extended-release tacrolimus formulations twice or once daily, respectively. Accuracy and precision of predicted concentrations were evaluated using mean absolute prediction error (MAPE), root mean square error (RMSE), and goodness of fit plots.

RESULTS

Only three models produced acceptable population predictions with the MAPE of < 50%. By using the Bayesian posthoc estimate of individual pharmacokinetic parameters, all models well performed with the MAPE and RMSE of < 30% and 40%, respectively, except two models; one could not successfully converge and the other substantially underpredicted tacrolimus concentrations.

CONCLUSION

We evaluated ten tacrolimus PopPK models, and eight models resulted in satisfactorily individual predicted tacrolimus concentrations in Thai kidney transplant patients and may be used to aid tacrolimus dose adjustment along with a clinical judgment.

Optimized In Silico Modeling of Drug Absorption after Gastric Bypass: The Case of Metformin

Bariatric surgery is an effective treatment for severe obesity and related comorbidities, such as type II diabetes. Gastric bypass surgery shortens the length of the intestine, possibly leading to altered drug absorption. Metformin, a first-line treatment for type II diabetes, has permeability-dependent drug absorption, which may be sensitive to intestinal anatomic changes during bypass surgery, including Roux-en-Y gastric bypass (RYGB). Previous computer simulation data indicate increased metformin absorption after RYGB. In this study, we experimentally determined the region-dependent permeability of metformin, using the rat single-pass intestinal perfusion method (SPIP), which we then implemented into GastroPlus^TM to assess the contribution of our SPIP data to post-RYGB metformin absorption modeling. Previous simulations allowed a good fit with in vivo literature data on healthy and obese control subjects. However, it was revealed that for post-RYGB drug absorption predictions, simply excluding the duodenum/jejunum is insufficient, as the software underestimates the observed plasma concentrations post-RYGB. By implementing experimentally determined segmental-dependent permeabilities for metformin in the remaining segments post-surgery, GastroPlus^TM proved to fit the observed plasma concentration profile, making it a useful tool for predicting drug absorption after gastric bypass. Reliable evaluation of the parameters dictating drug absorption is required for the accurate prediction of overall absorption after bariatric surgery.

Case Report: Predicting the Range of Lamotrigine Concentration Using Pharmacokinetic Models Based on Monte Carlo Simulation: A Case Study of Antiepileptic Drug-Related Leukopenia

Lamotrigine (LTG), a wide-spectrum antiepileptic drug, is frequently associated with cutaneous side-effects, whereas hematological side-effects such as leukopenia have rarely been reported for it. We report the case of a 15-year-old Chinese female epileptic patient weighing 60 kg who developed combined asymptomatic leukopenia after receiving concomitant therapy with LTG and valproate acid (VPA). In this case report, antiepileptic drug-related leukopenia may have occurred in definite relation to an increase in LTG concentration and reversed with the discontinuation of VPA. Monte Carlo (MC) simulations were performed to estimate the steady-state serum concentrations (C_ss) of LTG for different dosing regimens in adolescent Chinese epileptic patients weighing the same as the patient considered in the case study, based on pharmacokinetic (PK) models published in past research. Adjustments to the dosage of LTG for the patient were analyzed to illustrate the application of MC simulations and verify the results. The predicted LTG concentrations within a prediction interval between the 10th and 90th percentiles that represented 80% of the simulated populations, could adequately capture the measured LTG concentrations of the patient, indicating that MC simulations are a useful tool for estimating drug concentrations. Clinicians may benefit from the timely probabilistic predictions of the range of drug concentration based on an MC simulation that considers a large sample of virtual patients. The case considered here highlights the importance of therapeutic drug monitoring (TDM) and implementing model-informed precision dosing in the course of a patient’s individualized treatment to minimize adverse reactions.

pH-induced homogeneous liquid-liquid microextraction method based on new switchable deep eutectic solvent for the extraction of three antiepileptic drugs from breast milk

Aim: A pH-induced homogeneous liquid-liquid microextraction (HLLME) using a new switchable deep eutectic solvent has been used for the extraction of three antiepileptic drugs from breast milk samples. Methodology: This method is based on phase separation by changing pH. An ammonia solution and a phosphocholine chloride: hexanoic acid: p-aminophenol deep eutectic solvents were used as the phase separation agent and extraction solvent, respectively. Results: Significant factors were studied and the detection limits and enrichment factors were in the ranges of 0.009-0.19 ng ml^-1 and 182-212 for the analytes, respectively. Also, linear ranges were wide (0.63-500 ng ml^-1) and the method precision was acceptable. Conclusion: The introduced method was successfully applied for the determination of the analyte concentrations in breast milk samples.