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There is a significant rate of therapeutic failure in rheumatoid arthritis (RA) patients treated with leflunomide (LEF). This study investigates the utility values of teriflunomide levels (A77 1726) in identifying RA patients who remained with moderate or severe disease activity after the treatment with LEF. In this cross-sectional study, we compared: (a) RA patients who achieved a DAS28-ESR ≤ 3.2, and (b) RA patients who maintained a DAS28-ESR > 3.2 after treatment. ROC curves determined the cut-off of A77 1726 with the better performance to identify patients achieving a DAS28-ESR ≤ 3.2. Of the 115 patients treated with LEF, 69 (60%) remained with moderate/severe disease activity and 46 (40%) achieved low disease activity/remission. Higher A77 1726 levels showed a negative correlation with DAS28-ESR (r = - 0.42, p < 0.001) and other parameters of disease activity. We obtained the following utility values with the cut-off of A77 1726 > 10 µg/mL to identify RA patients who achieved a DAS28-ESR ≤ 3.2: sensitivity of 91.31%; specificity of 73.91%; positive predictive value of 70.00%; and negative predictive value of 92.73%. Serum A77 1726 discriminated between RA patients who remained with moderate/severe disease activity despite the treatment with LEF both as monotherapy and LEF as combo therapy., (© 2022. The Author(s).)

Objective: Leflunomide is a commonly used disease-modifying drug in the treatment of rheumatoid arthritis (RA). Its effects are mediated via inhibition of dihydroorotate dehydrogenase (DHODH) by its active metabolite teriflunomide, and the pharmacokinetics of teriflunomide are highly variable. Our objective was to examine the association between the DHODH haplotype and plasma teriflunomide concentration with response to leflunomide in patients with RA where leflunomide was added to an existing disease-modifying drug regimen after failure to achieve an adequate response with conventional triple therapy., Methods: Patients with RA who were taking, or were about to initiate, leflunomide were included. Participant characteristics, including the DHODH haplotype, were determined. Up to 5 plasma samples were collected after leflunomide was initiated for assays of total and free teriflunomide concentration. Disease activity was determined via the 28-joint Disease Activity Score (DAS28). The association between DAS28 scores and patient covariates was determined by linear mixed-effects modeling., Results: A total of 67 patients were included in the study. The DAS28 score after initiation of leflunomide was associated with the baseline DAS28 score (β = 0.70, P < 0.001) and was higher in those who carried the DHODH haplotype 2 (β = 0.56. P = 0.01) and did not carry the shared epitope (β = 0.56, P = 0.013). As total and free plasma teriflunomide concentration increased, the DAS28 score was significantly lower (P < 0.001 and P = 0.001, respectively). When considering threshold concentrations, teriflunomide concentrations >16 mg/liter were associated with a DAS28 score that was 0.33 lower, and when free teriflunomide concentration was >35 µg/liter, the DAS28 score was 0.32 lower., Conclusion: Teriflunomide concentration and carriage of the DHODH haplotype 2 are associated with response to leflunomide in patients with RA, and a total plasma teriflunomide concentration of at least 16 mg/liter is needed to maximize the likelihood of response., (© 2020, American College of Rheumatology.)

Teriflunomide is an oral first-line disease modifying treatment (DMT) for patients with relapsing-remitting multiple sclerosis (RRMS). It can take up to two years to achieve systemic clearance of teriflunomide to an acceptable level, but this washout period may be accelerated by administration of cholestyramine. Relapse of multiple sclerosis (MS) during washout of teriflunomide or other first-line DMT is not as common. We report two patients with RRMS who experienced a relapse after the accelerated elimination period (AEP) of teriflunomide and confirmation of negative plasmatic levels (<0.02 µg/ml). In cases of risk of MS activity, we should not wait for teriflunomide negative plasmatic levels confirmation before starting the next DMT to reduce the risk of relapse., Competing Interests: Declaration of Competing Interest The authors declare no conflicts of interest, (Copyright © 2020 Elsevier B.V. All rights reserved.)

A simple high-performance liquid chromatography coupled with tandem mass spectrometry method was developed and fully validated to simultaneously determine teriflunomide (TER) and its metabolite 4-trifluoro-methylaniline oxanilic acid (4-TMOA) in human plasma and urine. Merely 50 μL plasma and 20 μL urine were employed in sample preparation using protein precipitation and direct dilution method, respectively. An Agilent Zorbax eclipse plus C 18 column was selected to achieve rapid separation for TER and 4-TMOA within 3 min. Electrospray ionization under multiple reaction monitoring was used to monitor the ion transitions for TER (m/z 269.0 → 159.9), 4-TMOA (m/z 231.9 → 160.0), internal standard teriflunomide-d4 (m/z 273.0 → 164.0) and 2-amino-4-trifluoromethyl benzoic acid (m/z 203.8 → 120.1), operating in the negative ion mode. This method proved to have better accuracy and precision over concentration range of 10-5000 ng/mL in plasma as well as 10-10,000 ng/mL in urine. After a full validation, this method was successfully applied in a pharmacokinetic study of teriflunomide sodium and leflunomide in Chinese healthy volunteers., (© 2018 John Wiley & Sons, Ltd.)

Leflunomide's active metabolite teriflunomide inhibits dihydro-oroate dehydrogenase, an enzyme essential to proliferation of T lymphocytes. As teriflunomide must reach the target site to have this effect, this study assessed the distribution of teriflunomide into T lymphocytes, as intracellular concentrations may be a superior response biomarker to plasma concentrations. CD3 MicroBeads (Miltenyi Biotec, Bergisch Gladbach, Germany) were used to extract CD3 + T cells from the peripheral blood of patients with rheumatoid arthritis who were taking a stable dose of leflunomide. Unbound plasma and intra-CD3 + T cell teriflunomide concentrations were quantified using liquid chromatography-mass spectrometry. Concentration (log transformed) and partition differences were assessed through paired Student t tests. Sixteen patients provided plasma steady-state teriflunomide samples, and eight provided a sample 6-12 weeks later. At time-point one, the geometric mean teriflunomide concentration (range) in CD3 + T cells was 18.12 μg/L (6.15-42.26 μg/L) compared with 69.75 μg/L (32.89-263.1 μg/L) unbound in plasma (P < 0.001). The mean partition coefficient (range) for unbound plasma teriflunomide into CD3 + T cells was 0.295 (0.092-0.632), which was significantly different from unity (P < 0.001). The median (range) change in teriflunomide concentration between the two time points was 14% (-10% to 40%) in unbound plasma and -29% (-69 to 138%) for CD3 + T cells. Because teriflunomide concentrations in CD3 + T cells were lower and displayed a higher intraindividual variability than the unbound plasma concentrations, its applicability as a therapeutic drug-monitoring marker may be limited., (Copyright © 2016 by The American Society for Pharmacology and Experimental Therapeutics.)

This study describes a comparison between LC-UV and LC-MS method for the simultaneous analyses of a few disease-modifying agents of multiple sclerosis. Quantitative determination of fampridine (FAM), teriflunomide (TFM) and dimethyl fumarate (DMF) was performed in human plasma with the recovery values in the range of 85-115%. A reversed-phase high-performance liquid chromatography (HPLC) with UV as well as MS detection is used. The method utilizes an XBridge C18 silica column and a gradient elution with mobile phase consisting of ammonium formate and acetonitrile at a flow rate of 0.5 mL min(-1) . The method adequately resolves FAM, TFM and DMF within a run time of 15 min. Owing to low molecular weights, the estimation of DMF and FAM is more versatile in UV than MS detection. With LC-UV, the detection limits of FAM, TFM and DMF were 0.1, 0.05, 0.05 μg and the quantification limit for all the analytes was 1 μg. With LC-MS, the detection and quantification limits for all of the analytes were 1 and 5 ng, respectively. The two techniques were completely validated and shown to be reproducible and sensitive. They were applied to a pharmacokinetic study in rats by a single oral dose. Copyright © 2016 John Wiley & Sons, Ltd., (Copyright © 2016 John Wiley & Sons, Ltd.)

Background: Teriflunomide, a once-daily oral immunomodulator approved for treatment of relapsing-remitting multiple sclerosis, is eliminated slowly from plasma. If necessary to rapidly lower plasma concentrations of teriflunomide, an accelerated elimination procedure using cholestyramine or activated charcoal may be used. The current bioanalytical assay for determination of plasma teriflunomide concentration requires laboratory facilities for blood centrifugation and plasma storage. An alternative method, with potential for greater convenience, is dried blood spot (DBS) methodology. Analytical and clinical validations are required to switch from plasma to DBS (finger-prick sampling) methodology., Methods: Using blood samples from healthy subjects, an LC-MS/MS assay method for quantification of teriflunomide in DBS over a range of 0.01-10 mcg/mL was developed and validated for specificity, selectivity, accuracy, precision, reproducibility, and stability. Results were compared with those from the current plasma assay for determination of plasma teriflunomide concentration., Results: Method was specific and selective relative to endogenous compounds, with process efficiency ∼88%, and no matrix effect. Inaccuracy and imprecision for intraday and interday analyses were <15% at all concentrations tested. Quantification of teriflunomide in DBS assay was not affected by blood deposit volume and punch position within spot, and hematocrit level had a limited but acceptable effect on measurement accuracy. Teriflunomide was stable for at least 4 months at room temperature, and for at least 24 hours at 37°C with and without 95% relative humidity, to cover sampling, drying, and shipment conditions in the field. The correlation between DBS and plasma concentrations (R = 0.97), with an average blood to plasma ratio of 0.59, was concentration independent and constant over time., Conclusions: DBS sampling is a simple and practical method for monitoring teriflunomide concentrations.

Leflunomide is a prodrug used primarily for treatment of rheumatoid arthritis. The active metabolite, teriflunomide (A77 1726), inhibits the enzyme dihydroorotate dehydrogenase and thereby reduces the synthesis of pyrimidine ribonucleotides. Teriflunomide is also administered directly and finds use in treating multiple sclerosis. Therapeutic concentrations are generally in the tens of μg/mL serum or plasma and, due to adverse effects and the time required to reach steady state, therapeutic drug monitoring is beneficial. The drug is also a potential teratogen. A method was developed and validated to quantify the drug teriflunomide over a 40,000-fold concentration range of 5 ng/mL to 200 μg/mL in serum or plasma. This is accomplished by dividing the quantitative range into two separate but overlapping regions; a high curve and a low curve range. Samples are evaluated first against the high curve after a 100-fold dilution of the sample extract. Samples falling below the upper curve region are evaluated again without dilution and quantified, if possible, against the low curve calibration standards. Appropriate choice of a concentration for the deuterated internal standard (D4-teriflunomide) allows for a single, identical, extraction procedure to be performed for both curve regions but with the dilution performed for high curve samples. The method is rugged and reliable with good accuracy and precision statistics.

The intracellular transcription factor aryl hydrocarbon receptor (AHR) is bound and activated by xenobiotics, thereby promoting their catabolism by inducing expression of cytochrome P450 oxidase (CYP) genes through binding xenobiotic response elements (XRE) in their promoter region. In addition, it is involved in several cellular pathways like cell proliferation, differentiation, regeneration, tumor invasiveness and immune responses. Several pharmaceutical compounds like benzimidazoles activate the AHR and induce their own metabolic degradation. Using newly generated XRE-reporter mice, which allow in vivo bioluminescence imaging of AHR activation, we show here that the AHR is activated in vivo by teriflunomide (TER), which has recently been approved for the treatment of multiple sclerosis. While we did not find any evidence that the AHR mediates the immunomodulatory effects of TER, AHR activation led to metabolism and detoxification of teriflunomide, most likely via CYP. Mice deficient for the AHR show higher blood levels of teriflunomide, suffer from enhanced thrombo- and leukopenia and elevated liver enzymes as well as from severe gastrointestinal ulcers and bleeding which are lethal after 8-11 days of treatment. Leukopenia, acute liver damage and diarrhea have also been described as common side effects in human trials with TER. These data suggest that the AHR is relevant for detoxification not only of environmental toxins but also of drugs in clinical use, with potential implications for the application of AHR-modifying therapies in conjunction to TER in humans. The XRE-reporter mouse is a useful novel tool for monitoring AHR activation using in vivo imaging., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Background: A liquid chromatography tandem mass spectrometry (LC-MS/MS) method has been validated for use in therapeutic monitoring of the drug leflunomide in human serum and plasma. Because of concerns of teratogenicity, it is recommended that women who want to become pregnant have concentrations below 0.02 mcg/mL, although therapeutic levels are generally greater than 20 mcg/mL. Consequently, the method required a 40,000-fold dynamic range, which was achieved by dividing the curve range into 2 separate regions but with a single extraction procedure used for both., Methods: A chromatographic separation was achieved between the parent drug and the active metabolite, teriflunomide (A77 1726), and the latter was quantified across a quantitative range of 0.005-200 mcg/mL. Samples were evaluated in an upper curve region first, with dilution, to determine whether the drug concentrations were in an appropriate therapeutic range. Samples that fell below the upper region were then reevaluated in the lower region without dilution., Results: The method was shown to be reliable, with good accuracy and precision statistics, and acceptable quantitation using 4 different collection tube types. Mean accuracy over 6 control concentrations was within 5.4%, over 5 validation runs, whereas %coefficient of variation (CV) was within 8.15%. Evaluation of sodium heparin, KEDTA, NaF/K oxalate, and plain serum tubes from 6 separate individuals at the lower limit of quantification (LLOQ) showed no influence on the ability to quantify teriflunomide accurately. Regression equations for a curve range of 0.005-1 mcg/mL gave R values of 0.998 or better, whereas the range 0.8-200 mcg/mL had R values of 0.997 or better., Conclusions: The authors have developed and validated a method that allows quantification of leflunomide across a 40,000-fold range of 0.005-200 mcg/mL.

Leflunomide is a disease-modifying antirheumatic drug. The purpose of this study was to evaluate the bioequivalence of a test drug (CJ leflunomide) and a commercially available reference drug (Arava®) at 2 doses (10 and 20 mg) in healthy Korean volunteers. This was a single-dose (28 individuals enrolled at each dose group), randomized, open-label, 2-way crossover study. The 2 treatment periods were separated by a 56-day wash-out interval. Blood sampling was conducted until 672 h after drug administration. Plasma teriflunomide (active metabolite of leflunomide) concentrations were determined, and pharmacokinetic parameters were calculated. Bioequivalence was evaluated using an ANOVA model, based on the AUCt and the Cmax after administration of leflunomide tablets. Bioequivalence was defined as the 90% confidence intervals (CIs) of the geometric mean ratios (GMRs) of AUCt and Cmax for the test and reference drugs being within the range of 0.80-1.25. The GMRs (90% CI) for AUCt and Cmax were 0.9506 (0.9091-0.9941) and 0.9861 (0.9360-1.0389), respectively, in the 10 mg study, and 0.9524 (0.9101-0.9968) and 0.9740 (0.9314-1.0186), respectively, in the 20 mg study. The 90% CIs of AUCt and Cmax at each dose were within the accepted range for bioequivalence. Based on the results, the test drug (CJ leflunomide) was bioequivalent to the commercially available reference drug (Arava®) at both doses., (© Georg Thieme Verlag KG Stuttgart · New York.)

Pharmacokinetic data of disease modifying antirheumatic drugs during hemodialysis are limited to sulfasalazine, methotrexate, and cyclosporine. Only respective anecdotal data have been reported on leflunomide. We repeatedly measured teriflunomide (A77-1726), the active metabolite of leflunomide, during standard hemodialysis sessions and calculated teriflunomide clearances in five patients with rheumatoid arthritis (RA) and end-stage renal disease. The calculated teriflunomide clearances during a standardized dialysis session of 3-4.5 h at a blood flow rate of 160-300 ml/min were between 0 and 4.3 ml/min, the mean clearances of the total dialysis ranged between 1.1 and 3.4 ml/min. Total amount of teriflunomide removed was 5.8-8.8 μg per dialysis session. Dialytic removal of the active metabolite of leflunomide, teriflunomide (A77-1726), is negligible. Leflunomide can be used for RA patients on chronic dialysis without any dosage modification.

The pharmacokinetics of teriflunomide [CAS No. 163451-81-8], the metabolite of leflunomide [CAS No. 75706-12-6] has been evaluated in adult human volunteers after oral administration of tablet formulation. However, no published data is available regarding the bioavailability of this in the Indian population. In light of the above, a study was designed to carry out a bioequivalence study of 2 preparations of leflunomide 20 mg in healthy Indian male volunteers.24 healthy male volunteers (age, 25±4.1 years; weight, 57.58±7.01 kg) were enrolled in this study. Each subject received a test and reference formulation in a single dose, fasting 2 period, 2 way crossover study with a wash out period of 4 weeks. Analysis of teriflunomide from plasma samples was done by a simple and sensitive HPLC method using UV detection developed in our laboratory. An analysis of variance was performed on the pharmacokinetic parameters Cmax, AUC0-t, AUC0-∞ using GLM procedures in which sources of variation were subject, formulation, and period.The results indicated that there are no statistically significant differences between the 2 products in either the mean concentration-time profiles or in the obtained pharmacokinetic parameters. 90% confidence limits for the log transformed data of Cmax, AUC0-t, AUC0-∞. were within the acceptable range of 0.80-1.25.The results indicate that the 2 products are bioequivalent in terms of rate and extent of drug absorption. Both the preparations were well tolerated with no adverse reactions throughout the study., (© Georg Thieme Verlag KG Stuttgart · New York.)

The clinical activity of leflunomide, a drug used in the treatment of rheumatoid arthritis, is due to its active metabolite, teriflunomide. In vitro studies indicate that at least 99% of teriflunomide is expected to be protein bound in human plasma in vivo, leaving<1% in the unbound or 'free' state for clinical activity. To examine details of the relationships between leflunomide dosing and patient response, it is necessary to have an assay that is sufficiently sensitive to measure the minor fraction of free teriflunomide in patient samples. Therefore, we aimed to develop and validate an LC-MS/MS method for the measurement of teriflunomide, and use it to determine the total and free teriflunomide concentration in patients with rheumatoid arthritis. Teriflunomide and its deuterated internal standard were extracted from human plasma and separated using a reversed phase method with a C18 column. Detection was conducted with an API 3000 LC-MS/MS System by monitoring selected ions in negative ion MRM. Optimal detection occurred at m/z 269.1/160.0 (teriflunomide) and m/z 273.1/164.0 (teriflunomide-D4). Over a linear range of 5-500 μg/L, the inter-batch precision ranged from 1.9 to 8.8% and accuracy from -8.4 to 8.0%. The intra- and inter-batch assay precision for quality control samples ranged from 2.1-5.4% and 5.7-7.1% respectively. The procedure was applied to assess total and free plasma concentrations of teriflunomide in patients with rheumatoid arthritis. Free teriflunomide was approximately 0.11% of total teriflunomide, and there was a significant correlation (r2=0.724) between free and total teriflunomide concentrations. A validated, accurate and sensitive method was developed and successfully applied for the measurement of total and free teriflunomide concentration in human plasma samples. This method has been shown to be reproducible and sensitive and can be applied to clinical samples., (Copyright © 2011 Elsevier B.V. All rights reserved.)

A sensitive, selective and high throughput liquid chromatography tandem mass spectrometry (LC-ESI-MS/MS) method has been developed for the determination of teriflunomide, an active metabolite of leflunomide in human plasma. Plasma samples were prepared by liquid-liquid extraction of teriflunomide and valsartan as internal standard (IS) in ethyl acetate from 200microL human plasma. The chromatographic separation was achieved on an Inertsil ODS-3 C18 (50mmx4.6mm, 3microm) analytical column using isocratic mobile phase, consisting of 20mM ammonium acetate-methanol (25:75, v/v), at a flow-rate of 0.8mL/min. The precursor-->product ion transition for teriflunomide (m/z 269.0-->82.0) and IS (m/z 434.1-->350.3) were monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring (MRM) and negative ion mode. The method was validated over a wide dynamic concentration range of 10.1-4001ng/mL. Matrix effect was assessed by post-column infusion experiment and the mean process efficiency were 91.7% and 88.2% for teriflunomide and IS respectively. The method was rugged and rapid with a total run time of 2.0min and is applied to a bioequivalence study of 20mg leflunomide (test and reference) tablet formulation in 12 healthy Indian male subjects under fasting condition., (Copyright 2010 Elsevier B.V. All rights reserved.)

The respiratory stimulant prethcamide is a mixture of equal parts of crotethamide and cropropamide. A specific and sensitive gas chromatographic method for the determination of crotethamide and cropropamide in horse plasma and urine is described. Both components of prethcamide were extracted from plasma and urine into dichloromethane. The extracts were analyzed by capillary gas chromatography with thermionic detection in the nitrogen-specific detection mode. The lower limits of quantitation were 4.0 ng ml-1 of plasma and 10.0 ng ml-1 of urine. Calibration curves were linear from 2.0-100 ng ml-1 of plasma for both components. Pharmacokinetic parameters for crotethamide and cropropamide after intravenous and oral dosing were estimated by analysis of plasma concentration versus time data. The total plasma clearance of cropropamide was greater than that of crotethamide and both values were greater than 5 ml min-1 kg-1. Renal clearance values of the two drugs were comparable and were much less than estimates of filtration clearance values in horses, indicating extensive re-absorption of both components from the renal tubules. Both compounds were metabolized by N-demethylation of the [(dimethylamino)-carbonyl]-propyl moiety and these metabolites were excreted in urine. The method was demonstrated to be suitable for detecting illicit administration of prethcamide to competition horses.

Using the nucleolar test, the authors investigated the effects of the new Czechoslovak cytostatic agent Edikron (gamma, gamma-bis[4-ethylphenyl]-alpha, beta-dibromisocrotonic acid] on Wistar rats. The test showed that Edikron, administered perorally in the dose of 100 mg/kg BW per day for 5 days, affects neither the number of leukocytes nor the proteosynthetic activity of peripheral lymphocytes. The serum levels of Edikron, assessed with the aid of HPLC method 90 min after its last administration, averaged 14.03 +/- 1.63 micrograms/ml serum. Histological examination of the spleen, lymph nodes and thymus of the experimental and control groups also failed to detect any changes. However, the administration of Edikron elicited a statistically significant rise of erythrocytes in the experimental group, but the reason for that has not so far been ascertained.

A simple gas chromatographic method for the quantitative determination of ethyl butamide and propyl butamide, the active constituents of the analeptic drug "Prethcamide", in whole blood and tissues has been developed. The method was used to study the disposition of the compounds after iv and po administration to rabbits. The course of changes of ethyl butamide and propyl butamide concentration following rapid intravenous injection and oral administration was described by the two-compartment and one-compartment open models, respectively. The mean half-life (t1/2 beta, min), the body clearance (Clb, 1/min), the mean absorption rate constant (ka, min1-) and tmax (min) values were, respectively: 43.07 +/- 10.54, 0.05 +/- 0.0125, 0.033 +/- 0.0073 and 30.0 +/- 5.0 for ethyl butamide and 30.0 +/- 4.13, 0.0962 +/- 0.0269, 0.0512 +/- 0.0328 and 30.0 +/- 5.0 for propyl butamide. The low bioavailability (F) of the compounds, in the range 24-32%, may be attributed to low absorption of the drugs from the gastro-intestinal tract, or the first-pass effect, or both. The drugs accumulate predominantly in the liver. The faster metabolism and elimination of propyl butamide is postulated.