Development of LC-MS/MS determination method and backpropagation artificial neural networks pharmacokinetic model of febuxostat in healthy subjects.

WHAT IS KNOWN AND OBJECTIVE: Febuxostat is a well-known drug for treating hyperuricemia and gout. The published methods for determination of febuxostat in human plasma might be unsuitable for high-throughput determination and widespread application. We need to develop a highly selective, sensitive and rapid liquid chromatography-tandem mass spectrometry method. METHODS: The chromatographic separation was achieved on a Hypersil Gold-C18 (2.1 mm × 100 mm, 1.9 µm) column with mobile phase A (Water containing 0.1% formic acid) and mobile phase B (acetonitrile containing 0.1% formic acid). Multiple reaction monitoring (MRM) mode was used for quantification using target ions at m/z 315.3 â†’ m/z 271.3 for febuxostat and m/z 324.3 â†’ m/z 280.3 for Febuxostat-d9 (IS). A backpropagation artificial neural network (BPANN) pharmacokinetic model was constructed by the data of bioequivalence study. RESULTS AND DISCUSSION: After the LC-MS/MS method validated, it was successfully applied to the bioequivalence study of 30 human volunteers under fed condition. The predicted concentrations generated by BPANN model had a high correlation coefficient with experimental values. WHAT IS NEW AND CONCLUSION: A sensitive LC-MS/MS method had been developed and validated for determination of febuxostat in healthy subjects under fed condition, and a BPANN model was developed that can be used to predict the plasma concentration of febuxostat.

A pharmacokinetic-pharmacodynamic study of a single dose of febuxostat in healthy subjects.

AIMS: To examine the pharmacokinetic-phamacodynamic (PK-PD) relationships of plasma febuxostat and serum urate and the effect of a single dose of the drug on renal excretion and fractional clearance of urate (FCU). METHODS: Blood and urine samples were collected at baseline and up to 145 hours following administration of febuxostat (80 mg) to healthy subjects (n = 9). Plasma febuxostat and serum and urinary urate and creatinine concentrations were determined. Febuxostat pharmacokinetics were estimated using a two-compartment model with first-order absorption. An Emax PK-PD model was fitted to mean febuxostat and urate concentrations. Urinary urate excretion and FCU were calculated pre- and post-dose. RESULTS: Maximum mean plasma concentration of febuxostat (2.7 mg L-1 ) was observed 1.2 hours after dosage. Febuxostat initial and terminal half-lives were 2.0 ± 1.0 and 14.0 ± 4.7 hours (mean ± SD), respectively. The majority (81%) of the drug was eliminated in the 9 hours after dosing. Serum urate declined slowly achieving mean nadir (0.20 mmol L-1 ) at 24 hours. The IC50 (plasma febuxostat concentration that inhibits urate production by 50%) was 0.11 ± 0.09 mg L-1 (mean ± SD). Urinary urate excretion changed in parallel with serum urate. There was no systematic or significant change in FCU from baseline. CONCLUSION: The PK-PD model could potentially be used to individualise febuxostat treatment and improve clinical outcomes. A single dose of febuxostat does not affect the efficiency of the kidney to excrete urate. Further investigations are required to confirm the present results following multiple dosing with febuxostat.

Simultaneous determination of colchicine and febuxostat in rat plasma: Application in a rat pharmacokinetic study.

A selective, sensitive and rapid LC-MS/MS method has been developed and validated as per US Food and Drug Administration regulatory guidelines for the simultaneous quantitation of colchicine and febuxostat in rat plasma. Colchicine and febuxostat were extracted from the rat plasma using 10% tert-butyl methyl ether in ethyl acetate using colchicine-d6 as an internal standard (IS). The chromatographic separation of colchicine, febuxostat and the IS was achieved using a mobile phase comprising 5 mm ammonium formate and 0.025% formic acid in acetonitrile (20:80, v/v) in isocratic mode on an Eclipse XDB-C18 column. The injection volume and flow rate were 5.0 µl and 0.9 ml/min, respectively. Colchicine and febuxostat were detected by positive electrospray ionization in multiple reaction monitoring mode using transition pairs (Q1 → Q3) of m/z 400.10 → 358.10 and 317.05 → 261.00, respectively. The assay was linear in the ranges of 0.25-254 and 2.60-622 ng/ml for colchicine and febuxostat, respectively. The inter- and intra-day precision values were 0.58-13.0 and 1.03-4.88% for colchicine and febuxostat, respectively. No matrix or carryover effects were observed during the validation. Both analytes were stable on the bench-top, in the autosampler and in storage (freeze-thaw cycles and long-term storage at -80°C). A pharmacokinetic study in rats was performed to show the applicability of the validated method.

Development of an optimized febuxostat self-nanoemulsified loaded transdermal film: in-vitro, ex-vivo and in-vivo evaluation.

Febuxostat (FBX) is used to treat gout and chronic hyperuricemia. However, its bioavailability is moderate (49%) as a result of low solubility and first-pass metabolism. Therefore, the aim of our study is to improve FBX bioavailability by enhancement its solubility using self-nanoemulsifying drug delivery system (SNEDDS) technique in the form of transdermal film to avoid hepatic metabolism. To accomplish this goal, Eight SNEDDS formulae were prepared according to a three-factor, two-level D-Optimal mixture design to evaluate the effect of different ratios of the Lemon oil (X1), the surfactant Tween-20 (X2), and the co-surfactant PEG-400 (X3) on the globule size in order to reach smallest globular size. Results revealed that SNEDDS globule size ranged from 177 to 454 nm. The optimized formula consisted of 20% oil, 40% surfactant and 40% co-surfactant. Diffusion study showed improved enhancement in skin permeation that was confirmed by imaging using fluorescence microscope. In vivo plasma data showed significant (p < 0.05) difference in FBX plasma levels and pharmacokinetic parameters when compared with raw FBX loaded film. In conclusion, FBX-SNEDDS loaded transdermal film could be a successful way to improve solubility and skin permeability that would lead to improvement in patient's compliance.

Quality by Design Approach for the Development of Self-Emulsifying Systems for Oral Delivery of Febuxostat: Pharmacokinetic and Pharmacodynamic Evaluation.

The goal of the present investigation is to formulate febuxostat (FXT) self-nanoemulsifying delivery systems (liquid SNEDDS, solid SNEDDS, and pellet) to ameliorate the solubility and bioavailability. To determine the self-nanoemulsifying region, ternary plot was constructed utilizing Capmul MCM C8 NF® as an oil phase, Labrasol® as principal surfactant, and Transcutol HP® being the co-surfactant. Liquid SNEDDS (L-SNEDDS) were characterized by evaluating droplet size, zeta potential, % transmission, and for thermodynamic stability. In vitro dissolution study of FXT loaded L-SNEDDS (batch F7) showed increased dissolution (about 48.54 ± 0.43% in 0.1 N HCl while 86.44 ± 0.16% in phosphate buffer pH 7.4 within 30 min) compared to plain drug (19.65 ± 2.95% in 0.1 N HCl while about 17.61 ± 2.63% in phosphate buffer pH 7.4 within 30 min). Single pass intestinal permeability studies revealed fourfold increase in the intestinal permeability of F7 compared to plain drug. So, for commercial aspects, F7 was further transformed into solid SNEDDS (S-SNEDDS) as readily nanoemulsifying powder form (SNEP) as well as pellets prepared by application of extruder spheronizer. The developed formulation was found superior to pure FXT with enhanced oral bioavailability and anti-gout activity (with reduced uric acid levels), signifying a lipidic system being an efficacious substitute for gout treatment.

Verinurad combined with febuxostat in Japanese adults with gout or asymptomatic hyperuricaemia: a phase 2a, open-label study.

Objectives: Verinurad (RDEA3170) is a high-affinity inhibitor of the URAT1 transporter in clinical development for treating gout and asymptomatic hyperuricaemia. The aim of this Phase 2a, randomized, open-label study was to investigate the multiple-dose pharmacodynamics, pharmacokinetics and safety of oral verinurad combined with febuxostat vs febuxostat alone and verinurad alone. Methods: Japanese male subjects aged 21-65 years with gout (n = 37) or asymptomatic hyperuricaemia (n = 35) and serum urate (sUA) ⩾8 mg/dl were randomized to febuxostat (10, 20, 40 mg) in combination with verinurad (2.5-10 mg), verinurad alone (2.5-15 mg), febuxostat alone (10, 20, 40 mg) or benzbromarone alone (50 mg). There were four treatment periods per cohort and each treatment period was 7 days. Study drugs were administered once-daily after breakfast. Plasma, serum and urine samples were measured at pre-set intervals on days -1, 7, 14, 21 and 28. Results: Verinurad combined with febuxostat decreased sUA in dose-dependent manner, providing greater sUA lowering than febuxostat alone at the same dose (P < 0.001). Urinary uric acid excretion rate was increased by verinurad, reduced by febuxostat and comparable to baseline for verinurad combined with febuxostat. Verinurad from 2.5 mg to 15 mg was well tolerated, with no withdrawals due to adverse events. Laboratory assessments showed no clinically meaningful changes during combination treatment. Conclusion: Verinurad combined with febuxostat decreased sUA dose-dependently while maintaining uric acid excretion similar to baseline. All dose combinations of verinurad and febuxostat were generally well tolerated. These data support continued investigation of oral verinurad in patients with gout. Trial registration: ClinicalTrials.gov, https://clinicaltrials.gov, NCT02317861.

Comparison of Clinical Advantage between Topiroxostat and Febuxostat in Hemodialysis Patients.

To determine the response of hemodialysis (HD) patients to topiroxostat after a switch from febuxostat, we evaluated the efficacy, tolerability, and serum concentration of topiroxostat in HD patients after the switch. In this 16-month prospective observational study, we assessed the serum uric acid (UA) levels, other laboratory data, and serum topiroxostat concentrations of 10 HD patients who had been receiving febuxostat at a dose of 10 mg/d for over 1 year. No statistical difference was observed between the tolerability index at baseline and 16 months after the switch to topiroxostat. Serum UA after the switch in all patients (attained serum UA levels of ≤6 mg/dL) was 5.6±1.7 mg/dL (60%) at baseline, 4.9±0.5 mg/dL (100%) at 6 months and 5.7±0.4 mg/dL (50%) at 16 months (p=0.25), respectively. In patients with baseline serum UA levels >6 mg/dL, serum UA was significantly reduced at 6 and 16 months compared with baseline. Minimum serum concentrations of serum topiroxostat were lower than the limit of quantification (<25 ng/mL). Our results indicate that a switch from febuxostat 10 mg/d to topiroxostat 40 mg/d might reduce serum UA levels, with no change in other clinical laboratory data over the long term. These effects were more frequent in patients with high serum UA levels. Furthermore, topiroxostat therapy was more cost effective than febuxostat therapy. Thus, topiroxostat therapy could be a better treatment option for HD patients who develop high serum UA levels after febuxostat 10 mg/d administration.

Modeling and Simulation for Estimating the Influence of Renal Dysfunction on the Hypouricemic Effect of Febuxostat in Hyperuricemic Patients Due to Overproduction or Underexcretion of Uric Acid.

Whether renal dysfunction influences the hypouricemic effect of febuxostat, a xanthine oxidase (XO) inhibitor, in patients with hyperuricemia due to overproduction or underexcretion of uric acid (UA) remains unclear. We aimed to address this question with a modeling and simulation approach. The pharmacokinetics (PK) of febuxostat were analyzed using data from the literature. A kinetic model of UA was retrieved from a previous human study. Renal UA clearance was estimated as a function of creatinine clearance (CLcr) but non-renal UA clearance was assumed constant. A reversible inhibition model for bovine XO was adopted. Integrating these kinetic formulas, we developed a PK-pharmacodynamic (PK-PD) model for estimating the time course of the hypouricemic effect of febuxostat as a function of baseline UA level, febuxostat dose, treatment duration, body weight, and CLcr. Using the Monte Carlo simulation method, we examined the performance of the model by comparing predicted UA levels with those reported in the literature. We also modified the models for application to hyperuricemia due to UA overproduction or underexcretion. Thirty-nine data sets comprising 735 volunteers or patients were retrieved from the literature. A good correlation was observed between the hypouricemic effects of febuxostat estimated by our PK-PD model and those reported in the articles (observed) (r=0.89, p<0.001). The hypouricemic effect was estimated to be augmented in patients with renal dysfunction irrespective of the etiology of hyperuricemia. While validation in clinical studies is needed, the modeling and simulation approach may be useful for individualizing febuxostat doses in patients with various clinical characteristics.

Pharmacokinetics and tolerability of febuxostat after oral administration in healthy Chinese volunteers: a randomized, open-label, singleand multiple-dose three-way crossover study.

OBJECTIVE: Febuxostat is a novel non-purine selective inhibitor of xanthine oxidase indicated for the chronic management of hyperuricemia in patients with gout. The aim of the present study was to evaluate the pharmacokinetic properties and tolerability of single and multiple oral administrations of febuxostat capsules in healthy Chinese volunteers. METHODS: This openlabel, single- and multiple-dose three-way crossover study was conducted in healthy Chinese volunteers. Subjects were randomized to receive a single dose of febuxostat 40, 80, or 120 mg in separate trial periods, with a 1-week washout between periods. Those allocated to the 40 mg and 80 mg dose continued into the multiple-dose phase, in which they received 40 mg or 80 mg once daily for 6 consecutive days. During the course of the study, blood samples were collected and the concentrations of febuxostat were determined using LC-MS/MS. Pharmacokinetic parameters were estimated using a noncompartmental model. Tolerability was determined using clinical evaluation and monitoring of adverse events (AEs). RESULTS: 12 healthy Chinese volunteers were enrolled and completed 3 treatment periods. After oral administration of single doses of 40, 80, and 120 mg of febuxostat, the mean (SD) Cmax was 2,835.43 (1,136.41), 5,356.75 (1,711.33), and 7,718.21 (2,446.34) ng/mL, respectively; the AUC0-48h was 8,821.10 (3,018.35), 17,854.46 (5,113.28), and 30,832.05 (10,992.20) ng×h/ mL; the AUC0-∞ was 8,990.33 (3,046.14), 18,193.58 (5,160.80), and 31,466.93 (1,1074.74) ng×h/mL; the t1/2 was 5.95 (2.71), 9.41 (7.47), and 12.34 (10.34) hours; the Cl/F was 4.81 (1.18), 4.70 (1.21), and 4.18(1.19) L/h; and the Vz/F was 39.66 (16.69), 62.72 (51.41), and 73.41 (64.84) L. After administration of multiple doses of 40 and 80 mg febuxostat, the mean (SD) Cmax,ss was 2,762.38 (1,331.96) and 5,047.27 (1,456.57) ng/mL; the Cmin,ss was 124.10 (6.32) and 46.93 (15.86) ng/mL; the AUCss,0-τ was 8,525.49 (2,160.64) and 16,757.12 (4,223.17) ng×h /mL; the steadystate plasma concentration (Css) was 355.23 (90.03) and 698.21 (175.97) ng/mL; the t1/2 was 7.68 (3.30) and 11.33 (6.94) hours; the Cl/F was 4.99 (1.30) and 5.05 (1.22) L/h; and the Vz/F was 54.10 (24.10) and 85.51 (65.99) L. No serious AEs were reported, and there were no discontinuations due to AEs. CONCLUSION: The PK of febuxostat exhibited dose proportional kinetics from 40 to 120 mg dose. After multiple doses, the pharmacokinetic parameters of febuxostat were consistent with those after single doses. There was no accumulation in febuxostat exposure in healthy Chinese between multiple doses and single dose. At the doses studied, febuxostat appeared to be well tolerated in these healthy volunteers.

Population Pharmacokinetics and Therapeutic Efficacy of Febuxostat in Patients with Severe Renal Impairment.

The aim of the present study was to determine the influence of severe renal dysfunction (estimated glomerular filtration rate <30 ml/min/1.73 m(2), including hemodialysis) on the pharmacokinetics and therapeutic effects of febuxostat using a population pharmacokinetic analysis. This study recruited patients with hyperuricemia who were initially treated with allopurinol, but were switched to febuxostat, and it consists of 2 sub-studies: a pharmacokinetic study (26 patients) and retrospective efficacy evaluation study (51 patients). The demographic and clinical data of patients were collected from electronic medical records. Plasma febuxostat concentrations were obtained at each hospital visit. Population pharmacokinetic modeling was performed with NONMEM version 7.2. A total of 128 plasma febuxostat concentrations from 26 patients were used in the population pharmacokinetic analysis. The data were best described by a 1-compartment model with first order absorption. Covariate analysis revealed that renal function did not influence the pharmacokinetics of febuxostat, whereas actual body weight significantly influenced apparent clearance and apparent volume of distribution. The retrospective efficacy analysis showed the favorable therapeutic response of febuxostat switched from allopurinol in patients with moderate to severe renal impairment. No serious adverse event associated with febuxostat was observed irrespective of renal function. The population pharmacokinetic analysis and therapeutic analysis of febuxostat revealed that severe renal dysfunction had no influence on the pharmacokinetic parameters of febuxostat. These results suggest that febuxostat is tolerated well by patients with severe renal impairment.

Population pharmacokinetic analysis of febuxostat with high focus on absorption kinetics and food effect.

Febuxostat is commonly used in clinic for the treatment of hyperuricemia. Multiple-peak phenomenon has been observed in human plasma concentration-time profiles of febuxostat, but has not been paid enough attention in previous research. This study takes a pivotal step forward by conducting a comprehensive population pharmacokinetic (PopPK) analysis of febuxostat in a healthy Chinese cohort, with a central focus on delineating its absorption profile under contrasting fasting and fed conditions, while concurrently assessing the influence of food alongside other potential covariates on febuxostat's PK profile. The plasma concentration data used for modeling was obtained from two bioequivalence (BE) studies. Subjects were administered febuxostat 20 mg or 80 mg under fasting or fed condition. Goodness-of-fit plots, visual predict check (VPC), and normalized prediction distribution error (NPDE) were used for model evaluation. Based on the established model, PK profiles in healthy Caucasian subjects were simulated with parameter adjustment for race difference on clearance and bioavailability. Data from 128 subjects were used in the PopPK analysis. Febuxostat concentration-time curves were described by a two-compartment model with two deposit absorption compartments and lag times (Tlag). Prandial states (Food) showed significant impact on absorption rate ka1 and ka2, as well as Tlag1, and body weight was identified as a significant covariate on the apparent distribution volume. The PopPK analysis of febuxostat in healthy Chinese volunteers, under both fasted and fed conditions, successfully characterized its PK profile and underscored the significant influence of food on absorption. The potential difference of absorption between Chinese population and Caucasian population indicated from the simulations needs further investigation.

Febuxostat ternary inclusion complex using SBE7-ßCD in presence of a water-soluble polymer: physicochemical characterization, in vitro dissolution, and in vivo evaluation.

Febuxostat (FBX), a potent xanthine oxidase inhibitor, is widely used as a blood uric acid-reducing agent and has recently shown a promising repurposing outcome as an anti-cancer. FBX is known for its poor water solubility, which is the main cause of its weak oral bioavailability. In a previous study, we developed a binary system complex between FBX and sulfobutylether-ß-cyclodextrin (SBE7-ßCD) with improved dissolution behavior. The aim of the current study was to investigate the effect of incorporating a water-soluble polymer with a binary system forming a ternary one, on further enhancement of FBX solubility and dissolution rate. In vivo oral bioavailability was also studied using LC-MS/MS chromatography. The polymer screening study revealed a marked increment in the solubility of FBX with SBE7-ßCD in the presence of 5% w/v polyethylene glycol (PEG 6000). In vitro release profile showed a significant increase in the dissolution rate of FBX from FBX ternary complex (FTC). Oral in vivo bioavailability of prepared FTC showed more than threefold enhancement in Cmax value (17.05 ± 2.6 µg/mL) compared to pure FBX Cmax value (5.013 ± 0.417 µg/mL) with 257% rise in bioavailability. In conclusion, the association of water-soluble polymers with FBX and SBE7-ßCD system could significantly improve therapeutic applications of the drug.

Predicting gastric emptying of drug substances taken under postprandial conditions by combination of biorelevant dissolution and mechanistic in silico modeling.

Physiologically based pharmacokinetic (PBPK) models can help to understand the effects of gastric emptying on pharmacokinetics and in particular also provide a platform for understanding mechanisms of food effects, as well as extrapolation between different postprandial conditions, whether standardized clinical or patient-oriented, non-clinical conditions. By integrating biorelevant dissolution data from the GastroDuo dissolution model into a previously described mechanistic model of fed-state gastric emptying, we simulated the effects of a high-calorie high-fat meal on the pharmacokinetics of sildenafil, febuxostat, acetylsalicylic acid, theobromine and caffeine. The model was able to simulate the variability in Cmax and tmax caused by the presence of the stomach road. The main influences investigated to affect the gastric emptying process were drug solubility (theobromine and caffeine), tablet dissolution rate (acetylsalicylic acid) and sensitivity to gastric motility (sildenafil and febuxostat). Finally, we showed how PBPK models can be used to extrapolate pharmacokinetics between different prandial states using theobromine as an example with results from a clinical study being presented.

Comprehensive Evaluation of OATP- and BCRP-Mediated Drug-Drug Interactions of Methotrexate Using Physiologically-Based Pharmacokinetic Modeling.

Methotrexate (MTX) is an antifolate agent widely used for treating conditions such as rheumatoid arthritis and hematologic cancer. This study aimed to quantitatively interpret the drug-drug interactions (DDIs) of MTX mediated by drug transporters using physiologically-based pharmacokinetic (PBPK) modeling. An open-label, randomized, 4-treatment, 6-sequence, 4-period crossover study was conducted to investigate the effects of rifampicin (RFP), an inhibitor of organic anionic transporting peptides (OATP) 1B1/3, and febuxostat (FBX), an inhibitor of breast cancer resistance protein (BCRP), on the pharmacokinetics of MTX in healthy volunteers. PBPK models of MTX, RFP, and FBX were developed based on in vitro and in vivo data, and the performance of the simulation results for final PBPK models was validated in a clinical study. In the clinical study, when MTX was co-administered with RFP or FBX, systemic exposure of MTX increased by 33% and 17%, respectively, compared with that when MTX was administered alone. When MTX was co-administered with RFP and FBX, systemic exposure increased by 52% compared with that when MTX was administered alone. The final PBPK model showed a good prediction performance for the observed clinical data. The PBPK model of MTX was well developed in this study and can be used as a potential mechanistic model to predict and evaluate drug transporter-mediated DDIs of MTX with other drugs.

Discovery of a Potent and Orally Bioavailable Xanthine Oxidase/Urate Transporter 1 Dual Inhibitor as a Potential Treatment for Hyperuricemia and Gout.

The main uric acid-lowering agents in clinical use for hyperuricemia and gout are xanthine oxidase (XO) inhibitors or urate transporter 1 (URAT1) inhibitors. While these therapies can partially control the disease, they have various limitations. The development of XO/URAT1 dual inhibitors offers the potential to enhance therapeutic potency and reduce toxicity compared with single-target inhibitors. Through scaffold hopping from the XO inhibitor febuxostat (2) and the URAT1 inhibitor probenecid (3), followed by structure-activity relationship (SAR) studies, we identified compound 27 as a potent dual inhibitor of XO and URAT1. Compound 27 demonstrated significant dual inhibition in vitro (XO IC50 = 35 nM; URAT1 IC50 = 31 nM) and exhibited favorable pharmacology and pharmacokinetic (PK) profiles in multiple species including monkeys. Furthermore, toxicity studies in rats and monkeys revealed general safety profiles, supporting that compound 27 emerges as a promising novel drug candidate with potent XO/URAT1 dual inhibition for the treatment of gout.

Simultaneous determination of febuxostat and montelukast in human plasma using fabric phase sorptive extraction and high performance liquid chromatography-fluorimetric detection.

In the present work, a new sensitive and selective high-performance liquid chromatography-fluorimetric detection (HPLC-FLD) method was developed and validated to quantify febuxostat (FBX) and montelukast (MON) in human plasma. The developed procedure was successfully applied to a study aimed at evaluating the pharmacokinetic profiles of febuxostat and montelukast in human plasma. A sol-gel poly (caprolactone)-block-poly(dimethylsiloxane)-block-poly(caprolactone) (sol-gel PCAP-PDMS-PCAP) extraction sorbent coated fabric phase sorptive extraction membrane was used in the extraction process. The entire chromatographic analysis was performed with isocratic elution of the composition of the mobile phase (acetonitrile:water, 60:40, v:v, 0.032% glacial acetic acid) on the C18 column. The flow rate is varied during the analysis, particularly from 0.5 mL min-1 at the start and linearly increased to 1.5 mL min-1 in 7 min. The detection and quantification of the analytes was carried out by means of a fluorimetric detector at 320 nm and 350 nm as absorption wavelengths and at 380 and 400 nm as emission wavelengths for FBX and MON, respectively. The calibration curves demonstrated linearity in the range 0.3-10 ng mL-1 and 5-100 ng mL-1 for FBX and MON, respectively, while the LOD and LOQ values were 0.1 and 0.3 ng mL-1 for FBX and 1.5 and 5 ng mL-1 for MON. Intraday and interday RSD% values were found lower than 5.79%. As reported, the method was applied to real plasma samples obtained from a volunteer who was co-administered both the drugs. Pharmacokinetic data reveal that the concentration of both the drugs reaches the plateau approximately at the same time, but exhibits an elimination phase at different rates. This study demonstrated the usefulness of the new method and its applicability in therapeutic drug monitoring (TDM).

Formulation, characterization, optimization, and in-vivo performance of febuxostat self-nano-emulsifying system loaded sublingual films.

Febuxostat (FXS) is a potent antigout drug with poor water solubility and relative high first-pass effect leading to moderate oral bioavailability (<49%). This study aimed to increase FXS solubility and bioavailability by optimizing sublingual fast-dissolving films (SFs) containing a selected FXS self-nano-emulsifying system (s-SNES) previously prepared by our team. The s-SNES was loaded into SFs by solvent casting technique. A full factorial design (32) was applied to study the effects of polymer and plasticizer types on mechanical characteristics and the dissolution profile of FXS from the SFs. Numerical optimization was performed to select the SF having highest desirability according to predetermined characteristics. The optimized SF (O-SF) contained 1 g of s-SNES, polyvinylpyrrolidone K30 (6%w/v), polyethylene glycol 300 (20%w/w of polymer wt.), and Avicel PH101 (0.5%w/v). O-SF showed good permeation of FXS through sheep sublingual tissue. Storage of O-SF for three months showed no significant change in the FXS dissolution profile. In-vivo performance of O-SF in rabbits was compared to that of oral marketed tablets (Staturic® 80 mg). A cross-over design was applied and pharmacokinetic parameters were calculated after ensuring absence of sequence effect. Statistical analysis revealed better performance for O-SF with significantly higher Cmax, AUC0-24, AUC0-∞, apparent t1/2 together with lower tmax, and apparent kel than marketed tablets. Relative bioavailability of O-SF compared to the marketed tablet was found to be 240.6%. This confirms the achievement of the study aims of improving dissolution rate and bioavailability of FXS using a patient-wise convenient formula.

Combining Model-Based Clinical Trial Simulation, Pharmacoeconomics, and Value of Information to Optimize Trial Design.

The Bayesian decision-analytic approach to trial design uses prior distributions for treatment effects, updated with likelihoods for proposed trial data. Prior distributions for treatment effects based on previous trial results risks sample selection bias and difficulties when a proposed trial differs in terms of patient characteristics, medication adherence, or treatment doses and regimens. The aim of this study was to demonstrate the utility of using pharmacometric-based clinical trial simulation (CTS) to generate prior distributions for use in Bayesian decision-theoretic trial design. The methods consisted of four principal stages: a CTS to predict the distribution of treatment response for a range of trial designs; Bayesian updating for a proposed sample size; a pharmacoeconomic model to represent the perspective of a reimbursement authority in which price is contingent on trial outcome; and a model of the pharmaceutical company return on investment linking drug prices to sales revenue. We used a case study of febuxostat versus allopurinol for the treatment of hyperuricemia in patients with gout. Trial design scenarios studied included alternative treatment doses, inclusion criteria, input uncertainty, and sample size. Optimal trial sample sizes varied depending on the uncertainty of model inputs, trial inclusion criteria, and treatment doses. This interdisciplinary framework for trial design and sample size calculation may have value in supporting decisions during later phases of drug development and in identifying costly sources of uncertainty, and thus inform future research and development strategies.

Febuxostat, But Not Allopurinol, Markedly Raises the Plasma Concentrations of the Breast Cancer Resistance Protein Substrate Rosuvastatin.

Xanthine oxidase inhibitors febuxostat and allopurinol are commonly used in the treatment of gout. Febuxostat inhibits the breast cancer resistance protein (BCRP) in vitro. Rosuvastatin is a BCRP substrate and genetic variability in BCRP markedly affects rosuvastatin pharmacokinetics. In this study, we investigated possible effects of febuxostat and allopurinol on rosuvastatin pharmacokinetics. In a randomized crossover study with 3 phases, 10 healthy volunteers ingested once daily placebo for 7 days, 300 mg allopurinol for 7 days, or placebo for 3 days, followed by 120 mg febuxostat for 4 days, and a single 10 mg dose of rosuvastatin on day 6. Febuxostat increased the peak plasma concentration and area under the plasma concentration-time curve of rosuvastatin 2.1-fold (90% confidence interval 1.8-2.6; P = 5 × 10-5 ) and 1.9-fold (1.5-2.5; P = 0.001), but had no effect on rosuvastatin half-life or renal clearance. Allopurinol, on the other hand, did not affect rosuvastatin pharmacokinetics. In vitro, febuxostat inhibited the ATP-dependent uptake of rosuvastatin into BCRP-overexpressing membrane vesicles with a half-maximal inhibitory concentration of 0.35 µM, whereas allopurinol showed no inhibition with concentrations up to 200 µM. Taken together, the results suggest that febuxostat increases rosuvastatin exposure by inhibiting its BCRP-mediated efflux in the small intestine. Febuxostat may, therefore, serve as a useful index inhibitor of BCRP in drug-drug interaction studies in humans. Moreover, concomitant use of febuxostat may increase the exposure to BCRP substrate drugs and, thus, the risk of dose-dependent adverse effects.

Determination of febuxostat in human plasma by high performance liquid chromatography (HPLC) with fluorescence-detection.

Febuxostat prevents gout attacks by lowering serum urate. Aspects of the pharmacokinetic-pharmacodynamic relationship of febuxostat concentrations to urate in gout patients need further elucidation. In order to undertake these studies, the assay methodology for febuxostat has been enhanced and validated to meet FDA standards. An HPLC method with fluorescence-detection has been modified to increase sensitivity, reduce complexity, shorten the sample preparation process and improve the inter-day coefficient of variation of the lowest quality control sample (0.03 µg/L). Protein in plasma samples (200 µL) is now precipitated with acetonitrile (400 µL) containing the internal standard (2-naphthoic acid). The supernatant is analysed at excitation and emission wavelengths of 320 and 380 nm, respectively as in the previous method. A Luna C18 column (Phenomenex, Australia) at 40 °C with mobile phase of glacial acetic acid (0.032%) in acetonitrile:water (60:40, v:v), an injection volume of 10 µL and a flow rate of 1.5 mL/min is employed. Analysis time is 8 min. Calibration curves in drug-free plasma range from 0.005 to 10.00 µg/mL. Data points are fitted using linear regression with a weighting factor of 1/concentration. The inter-day accuracy and imprecision of the quality control samples (0.0075, 0.015, 3.00 and 9.80 µg/mL) is 90-115% and ≤ 14.5%, respectively.