Semiphysiologically Based Pharmacokinetic Model of Leflunomide Disposition in Rheumatoid Arthritis Patients

Development of a population pharmacokinetic model and optimal dosing regimen of leflunomide in Korean population

PURPOSE

Leflunomide is an immunosuppressive drug indicated for the treatment of rheumatoid arthritis (RA). While the pharmacokinetics (PK) of its active metabolite A771726 reportedly show large interindividual variability, no efficient dose individualization strategy is currently available. The goal of this work was to develop a population PK model for A771726 and propose an optimal individualized dosing strategy.

METHODS

A771726 plasma concentration data were collected from 50 healthy male volunteers participating in two leflunomide PK studies given a single oral dose of 40 mg. Concentrations were elevated in low body weight (WT) subjects and showed multiple peaks. Thus, A771726 PK modeling was conducted incorporating allometry scaling and enterohepatic circulation (EHC). For dose optimization, simulating a set of 1000 virtual subjects from the developed model and dividing the subjects into 5 groups with WT of 50, 60, 70, 80, 90 kg, respectively, the optimal dose was explored that achieves the drug concentration most similar to the target, which was defined as the concentration for the 70 kg subject treated with the current standard dosage regimen (the loading dose of 100 mg QD for 3 days, followed by the maintenance dose of 20 mg QD).

RESULTS

The data were best described by a two compartment model with first order absorption incorporating EHC with the bile released into the intestine. None of the covariates tested was found to be significant other than WT used in allometry. Simulation showed that the optimal loading dose increased by 15 mg for every 10 kg increment in WT while the optimal maintenance dose was 15 and 25 mg for 50 and 90 kg groups, respectively, and the same (= 20 mg) for the others. Large concentration differences from the target observed in low and high WT groups disappeared when optimal doses were given.

CONCLUSIONS

This work demonstrates the importance of a population PK model-based dose optimization approach in maintaining drug therapeutic concentrations in leflunomide treatment.

Frequency and impact of DHODH, ABCG2 and CYP2C19 SNPs on the therapeutic efficacy, tolerability and toxicity of leflunomide

Introduction: Leflunomide is one of the commonly used drugs in treatment of rheumatoid arthritis (RA), which on administration is converted into its active metabolite teriflunomide. Aim: Our aim is to evaluate the frequencies of dihydrooroate dehydrogenase (DHODH) (rs3213422), ABCG2 (rs2231142) and CYP2C19 (rs4244285) allele distribution among patients receiving leflunomide for RA and their possible impact on leflunomide performance in disease control. Patients & methods: Patients (>18 years) who fulfilled the 2010 ACR classification criteria for RA receiving leflunomide (20 mg/day) were included in the study. Disease activity score 28 was used to assess patients disease activity. Blood samples were collected for full blood count and blood chemistry. Genomic DNA was extracted from peripheral blood. The selection of SNPs was based on the criteria of minor allele frequency among Caucasians. Results: A significant association between the therapeutic outcome of leflunomide and DHODH genotyping was observed but not with CYP2C19 and ABCG2. Importantly, there is a significant association between DHODH (rs3213422) CC genotype and the number of patients with controlled disease. Conclusion: We strongly suggest that polymorphisms in the DHODH are the major factor affecting leflunomide pharmacogenetics and therapeutic efficacy.

The Mitochondria-Independent Cytotoxic Effect of Leflunomide on RPMI-8226 Multiple Myeloma Cell Line

Leflunomide, an anti-inflammatory agent, has been shown to be effective in multiple myeloma (MM) treatment; however, the mechanism of this phenomenon has not been fully elucidated. The aim of the study was to assess the role of mitochondria and dihydroorotate dehydrogenase (DHODH) inhibition in the cytotoxicity of leflunomide in relation to the MM cell line RPMI 8226. The cytotoxic effect of teriflunomide-an active metabolite of leflunomide-was determined using MTT assay, apoptosis detection, and cell cycle analysis. To evaluate DHODH-dependent toxicity, the cultures treated with teriflunomide were supplemented with uridine. Additionally, the level of cellular thiols as oxidative stress symptom was measured as well as mitochondrial membrane potential and protein tyrosine kinases (PTK) activity. The localization of the compound in cell compartments was examined using HPLC method. Teriflunomide cytotoxicity was not abolished in uridine presence. Observed apoptosis occurred in a mitochondria-independent manner, there was also no decrease in cellular thiols level. Teriflunomide arrested cell cycle in the G2/M phase which is not typical for DHODH deficiency. PTK activity was decreased only at the highest drug concentration. Interestingly, teriflunomide was not detected in the mitochondria. The aforementioned results indicate DHODH- and mitochondria-independent mechanism of leflunomide toxicity against RPMI 8226 cell line.

Evidence-Based Guidelines for Drug Interaction Studies: Model-Informed Time Course of Intestinal and Hepatic CYP3A4 Inhibition by Clarithromycin

Drug-drug interaction (DDI) studies are mandated in drug development; however, protocols for evaluating the impact of cytochrome P450 (CYP) inhibition on new molecular entities are currently inconsistent. This study utilised validated physiologically based pharmacokinetic (PBPK) software to define the optimal dose, frequency, and duration of clarithromycin to achieve optimal characterisation of CYP3A4 inhibition in a study population. The Simcyp® Simulator (Version 19.0) was used to simulate clarithromycin-mediated CYP3A4 inhibition in healthy virtual cohorts. Between trial variability in magnitude and time course of CYP3A4 activity was assessed following clarithromycin dosing strategies obtained from the University of Washington Drug Interaction Database. Heterogeneity in CYP3A4 inhibition was evaluated across sex, race, and age. Literature review identified 500 mg twice daily for 5 days as the most common clarithromycin dosing protocol for CYP3A4 inhibition studies. On simulation, clarithromycin 500 mg twice daily resulted in the largest steady-state inhibition of hepatic (percent mean inhibition [95%CI] = 80 [77-83]) and small intestine (94 [94-95]) CYP3A4 activity (as compared to 500 mg once daily, 400 mg once/twice daily, or 250 mg once/twice daily). Additionally, 500 mg twice daily was associated with the shortest time for 90% of individuals to reach 90% of their minimum hepatic (4 days) and small intestine (1 days) CYP3A4 activity. The study presented herein supports that clarithromycin dosing protocol of 500 mg twice daily for 5 days is sufficient to achieve maximal hepatic and small intestine CYP3A4 inhibition. These findings were consistent between sex, race, and age differences.

Pharmacokinetics and Bioequivalence Studies of Teriflunomide in Healthy Iranian Volunteers

Multiple sclerosis, which is characterized by inflammation and neurodegeneration, is considered a chronic disease of the central nervous system. Given the lack of pharmacokinetic evaluation of teriflunomide in the Iranian context, the present 2-way crossover study aimed to assess the pharmacokinetic properties and bioequivalence of 2 teriflunomide formulations. To this end, 2 single-dose generic and branded teriflunomide formulations were orally administered to 14 healthy Iranian male volunteers. A washout period of 21 days was allowed between the treatments. The plasma samples containing teriflunomide were analyzed by a simple and sensitive high-performance liquid chromatography method using standard ultraviolet detection. In addition, the pharmacokinetic parameters were calculated for bioequivalence evaluation. The peak area ratio between the teriflunomide and the internal standard was the source of calibration curves, which were linear over the range of 20-40,000 ng/mL (R² = 0.9994). The results indicated that the 2 formulations had similar pharmacokinetics. Further, the 90%CI of the mean ratios of the test versus the reference formulations of log-transformed area under the concentration-time curve over 72 hours (93% to 107%) and peak concentration (92% to 108%) were within the acceptable range of 80% to 125%. Based on the obtained results, the test formulation of teriflunomide could be similar to that of the reference formulation.

Clinical Pharmacokinetic Monitoring of Leflunomide in Renal Transplant Recipients with BK Virus Reactivation: A Review of the Literature

Leflunomide is an immunosuppressive drug with in vitro and initial observational evidence of antiviral activity against BK virus (BKV), a pathogen that causes opportunistic infection upon reactivation in renal transplant recipients. Leflunomide is considered an ancillary option to immunosuppression reduction in the management of BKV reactivation. Plasma or blood concentrations of teriflunomide, the active metabolite of leflunomide, are commonly monitored because of high leflunomide doses being used, known inter-individual variability in pharmacokinetics, and hepatotoxicity risk. However, the utility of clinical pharmacokinetic monitoring for leflunomide is as yet unclear. A literature search of MEDLINE (1946-December 2016), EMBASE (1974-December 2016), the CENTRAL database, and Google Scholar was performed to identify relevant English-language articles. Further articles were identified from references in relevant literature. A previously published 9-step decision-making algorithm was used to assess the available literature and determine the utility of clinical pharmacokinetic monitoring for leflunomide. Teriflunomide is readily measurable in the plasma or blood, but a clear relationship between concentration and efficacy or toxicity is lacking, and its therapeutic range is not well-established. Efficacy and toxicity endpoints such as renal function and BKV clearance can be readily assessed without measuring teriflunomide concentrations. Pharmacokinetic parameters are affected by genetic polymorphisms in cytochrome P450 CYP2C19 and ABCG2 genes. Therefore, routine clinical pharmacokinetic monitoring of leflunomide cannot be recommended based on current available evidence. However, it may provide clinical benefit in difficult situations when patients demonstrate a lack of therapeutic response or exhibit signs of drug toxicity.

Putting recommendations into practice: Australian rheumatologists' opinions on leflunomide use in rheumatoid arthritis

Leflunomide is the most recently introduced conventional disease-modifying anti-rheumatic drugs in Australia. It has several unique methods for initiation, unique monitoring recommendations and a distinctive cessation protocol in the event of serious toxicity. The aim of this study was to evaluate initiation and monitoring practices of Australian rheumatologists using leflunomide. A survey was emailed twice, approximately 3 months apart to 332 rheumatologist members of the Australian Rheumatology Association. Wave analysis was used to assess evidence of non-response bias. The response rate to the survey was 20% and there was no difference between the responses of waves 1 and 2. Fifty percent of the respondents indicated that 20 mg once daily was the initial dose of leflunomide that they most commonly prescribed, 45% indicated 10 mg once daily, whilst only 3% preferred to initiate leflunomide at 100 mg daily for 2-3 days followed by 10 mg once a day as recommended when first marketed. Of the responders, 12% had used doses above 20 mg daily and 70% had used alternate daily dosing with leflunomide. In a patient taking leflunomide with an ALT or AST >3 times the ULN on two or more blood tests, 75% of responders indicated they would stop leflunomide immediately and 20% would follow cessation by administering a cholestyramine washout. The choice of initial leflunomide dose among responding Australian rheumatologists varied considerably, although most preferred not to use the loading dose. Despite the recommendation of clinical guidelines, the use of a cholestyramine washout procedure for hepatic toxicity is not universal.

An introduction to physiologically-based pharmacokinetic models

Physiologically-based pharmacokinetic (PBPK) models represent drug kinetics in one or more 'real' organs (and hence require submodels of organs/tissues) and they describe 'whole-body' kinetics by joining together submodels with drug transport by blood flow as dictated by anatomy. They attempt to reproduce 'measureable' physiological and/or pharmacokinetic processes rather than more abstract rate constants and volumes. PBPK models may be built using a 'bottom-up' approach, where parameters are chosen from first principles, literature, or in vitro data as opposed to a 'top-down' approach, where all parameters are estimated from data. The basic principles of PBPK models are described, focusing on the equations for three individual organs: a single flow-limited compartment describing distribution only, a membrane-limited compartment describing distribution, and a single flow-limited compartment with elimination. These organ models are linked to make a basic three-compartment physiological model of the whole body. PBPK models are particularly suited to scaling kinetics across body size (e.g., adult to neonate) and species (e.g., animal to first-in-man) as physiology and pharmacology can be represented by independent parameters. Maturation models can be incorporated as for compartmental models. PBPK models are now available in commercial software packages, and are perhaps now more accessible than ever. Alternatively, even complex PBPK models can be represented in generic differential equation-solving software using the simple principles described here. The relative ease of constructing the code for PBPK models belies the most difficult aspect of their implementation-collecting, collating, and justifying the data used to parameterize the model.

Genetic polymorphism of CYP1A2 but not total or free teriflunomide concentrations is associated with leflunomide cessation in rheumatoid arthritis

AIM

Leflunomide, via its active metabolite teriflunomide, is used in rheumatoid arthritis (RA) treatment, yet approximately 20 to 40% of patients cease due to toxicity. The aim was to develop a time-to-event model describing leflunomide cessation due to toxicity within a clinical cohort and to investigate potential predictors of cessation such as total and free teriflunomide exposure and pharmacogenetic influences.

METHODS

This study included individuals enrolled in the Early Arthritis inception cohort at the Royal Adelaide Hospital between 2000 and 2013 who received leflunomide. A time-to-event model in nonmem was used to describe the time until leflunomide cessation and the influence of teriflunomide exposure and pharmacogenetic variants. Random censoring of individuals was simultaneously described. The clinical relevance of significant covariates was visualized via simulation.

RESULTS

Data from 105 patients were analyzed, with 34 ceasing due to toxicity. The baseline dropout hazard and baseline random censoring hazard were best described by step functions changing over discrete time intervals. No statistically significant associations with teriflunomide exposure metrics were identified. Of the screened covariates, carriers of the C allele of CYP1A2 rs762551 had a 2.29 fold increase in cessation hazard compared with non-carriers (95% CI 2.24, 2.34, P = 0.016).

CONCLUSIONS

A time-to-event model described the time between leflunomide initiation and cessation due to side effects. The C allele of CYP1A2 rs762551 was linked to increased leflunomide toxicity, while no association with teriflunomide exposure was identified. Future research should continue to investigate exposure-toxicity relationships, as well as potentially toxic metabolites.

Population pharmacokinetic modeling of itraconazole and hydroxyitraconazole for oral SUBA-itraconazole and sporanox capsule formulations in healthy subjects in fed and fasted states

Itraconazole is an orally active antifungal agent that has complex and highly variable absorption kinetics that is highly affected by food. This study aimed to develop a population pharmacokinetic model for itraconazole and the active metabolite hydroxyitraconazole, in particular, quantifying the effects of food and formulation on oral absorption. Plasma pharmacokinetic data were collected from seven phase I crossover trials comparing the SUBA-itraconazole and Sporanox formulations of itraconazole. First, a model of single-dose itraconazole data was developed, which was then extended to the multidose data. Covariate effects on itraconazole were then examined before extending the model to describe hydroxyitraconazole. The final itraconazole model was a 2-compartment model with oral absorption described by 4-transit compartments. Multidose kinetics was described by total effective daily dose- and time-dependent changes in clearance and bioavailability. Hydroxyitraconazole was best described by a 1-compartment model with mixed first-order and Michaelis-Menten elimination for the single-dose data and a time-dependent clearance for the multidose data. The relative bioavailability of SUBA-itraconazole compared to that of Sporanox was 173% and was 21% less variable between subjects. Food resulted in a 27% reduction in bioavailability and 58% reduction in the transit absorption rate constant compared to that with the fasted state, irrespective of the formulation. This analysis presents the most extensive population pharmacokinetic model of itraconazole and hydroxyitraconazole in the literature performed in healthy subjects. The presented model can be used for simulating food effects on itraconazole exposure and for performing prestudy power analysis and sample size estimation, which are important aspects of clinical trial design of bioequivalence studies.