Ultra-performance hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry for simultaneous determination of allopurinol, oxypurinol and lesinurad in rat plasma: Application to pharmacokinetic study in rats

Mechanosynthesis of Stable Salt Hydrates of Allopurinol with Enhanced Dissolution, Diffusion, and Pharmacokinetics

Allopurinol (ALO) is a medication that treats gout and kidney stones by lowering uric acid synthesis in the blood. The biopharmaceutics classification system (BCS) IV drug exhibits poor aqueous solubility, permeability, and bioavailability. To overcome the bottlenecks of ALO, salts with maleic acid (MLE) and oxalic acid (OXA) were synthesized using the solvent-assisted grinding method. The novel multicomponent solids were characterized by PXRD, DSC, TGA, FT-IR, and SEM images. The crystal structures of these salts with variable stoichiometry were obtained using Rietveld refinement from the high-resolution PXRD data. The proton from the dicarboxylic acid is transferred to the most basic pyrimidine "N" of ALO. The N-H···N hydrogen-bonded ALO homodimer is replaced by the N+-H···O- ionic interactions in ALO-OXA (2:1:0.4) and ALO-MLE (1:1:1) salt hydrates. The organic salts improved solubility and dissolution up to 5-fold and the diffusion permeability up to 12 times compared to the native drug in a luminal pH 6.8 phosphate buffer medium. The salt hydrates were exceptionally stable during storage at 30 ± 5 °C and 75 ± 5% relative humidity. Superior dissolution and diffusion permeability of the ALO-MLE salt resulted in improved pharmacokinetics (peak plasma concentration) that offers a promising solid dosage form with enhanced bioavailability and lower dosage formulation.

Mesoporous Silica Nanoparticles Coated with Carboxymethyl Chitosan for 5-Fluorouracil Ocular Delivery: Characterization, In Vitro and In Vivo Studies

This study investigates the development of topically applied non-invasive amino-functionalized silica nanoparticles (AMSN) and O-Carboxymethyl chitosan-coated AMSN (AMSN-CMC) for ocular delivery of 5-Fluorouracil (5-FU). Particle characterization was performed by the DLS technique (Zeta-Sizer), and structural morphology was examined by SEM and TEM. The drug encapsulation and loading were determined by the indirect method using HPLC. Physicochemical characterizations were performed by NMR, TGA, FTIR, and PXRD. In vitro release was conducted through a dialysis membrane in PBS (pH 7.4) using modified Vertical Franz diffusion cells. The mucoadhesion ability of the prepared nanoparticles was tested using the particle method by evaluating the change in zeta potential. The transcorneal permeabilities of 5-FU from AMNS-FU and AMSN-CMC-FU gel formulations were estimated through excised goat cornea and compared to that of 5-FU gel formulation. Eye irritation and ocular pharmacokinetic studies from gel formulations were evaluated in rabbit eyes. The optimum formulation of AMSN-CMC-FU was found to be nanoparticles with a particle size of 249.4 nm with a polydispersity of 0.429, encapsulation efficiency of 25.8 ± 5.8%, and drug loading capacity of 5.2 ± 1.2%. NMR spectra confirmed the coating of AMSN with the CMC layer. In addition, TGA, FTIR, and PXRD confirmed the drug loading inside the AMSN-CMC. Release profiles showed 100% of the drug was released from the 5-FU gel within 4 h, while AMSN-FU gel released 20.8% of the drug and AMSN-CMC-FU gel released around 55.6% after 4 h. AMSN-CMC-FU initially exhibited a 2.45-fold increase in transcorneal flux and apparent permeation of 5-FU compared to 5-FU gel, indicating a better corneal permeation. Higher bioavailability of AMSN-FU and AMSN-CMC-FU gel formulations was found compared to 5-FU gel in the ocular pharmacokinetic study with superior pharmacokinetics parameters of AMSN-CMC-FU gel. AMSN-CMC-FU showed 1.52- and 6.14-fold higher AUC0-inf in comparison to AMSN-FU and 5-FU gel, respectively. AMSN-CMC-FU gel and AMSN-FU gel were "minimally irritating" to rabbit eyes but showed minimal eye irritation potency in comparison to the 5 FU gel. Thus, the 5-FU loaded in AMSN-CMC gel could be used as a topical formulation for the treatment of ocular cancer.

Synthesis and drug release properties of melanin added functional allopurinol incorporated starch-based biomaterials

The main objective of this study was to prepare functional allopurinol (ALP) incorporated biomaterials using mungbean starch, polyvinyl alcohol, melanin (MEL), and plasticizers. Prepared biomaterials were characterized by FE-SEM and FT-IR analysis. Photothermal conversion efficiencies and ALP release properties of biomaterials were evaluated with NIR laser irradiation. When biomaterials were irradiated with the NIR laser, temperatures increase of MEL-added biomaterials were higher than those of MEL-non-added biomaterials. After NIR laser irradiation, ALP release rates of MEL-added biomaterials were 1.62 times faster than those of MEL-non-added biomaterials. In addition, ALP release using an artificial skin was increased by NIR laser irradiation. ALP release from biomaterials followed Fickian diffusion mechanism, while ALP release using an artificial skin followed a non-Fickian diffusion mechanism. Xanthine oxidase inhibitory (%) for MEL-added biomaterials with/without the addition of GL and XL were 47.5%, 61.7%, and 65.1%, respectively.

Sample preparation and quantification of polar drug, allopurinol, in human plasma using LCMSMS

A fast, selective and reproducible LC-MS/MS method with simple sample preparation was developed and validated for a polar compound, allopurinol in human plasma, using acyclovir as internal standard (IS). Chromatographic separation was achieved using Agilent Poroshell 120 EC-C₁₈ (100 × 2.1 mmID, 2.7 µm) analytical column. The mobile phase was comprised of 0.1%v/v formic acid-methanol (95:05; v/v), at a flow rate of 0.45 mL/min. The effect of different protein precipitation agents used in sample preparation such as methanol, acetonitrile, a mixture of acetonitrile-methanol and a mixture of acetonitrile-acetone were evaluated to optimize the extraction efficiency of allopurinol and IS. The use of acetone-acetonitrile (50:50, v/v) as protein precipitating agent shortened the sample preparation time and improved the recovery of allopurinol to above 93%. The IS-normalised matrix factors at two concentration levels were 1.0, with CV of 5.1% and 4.2%. Allopurinol in plasma was stable at benchtop for 24 h, in autosampler tray for 48 h, in instrumentation room for 48 h, in freezer after 7 freeze-thaw cycles and in freezer for 140 days. Allopurinol stock standard solutions were stable for 140 days at room temperature and in the chiller. The short sample run time of the validated bioanalytical method allowed high throughput analysis of plasma samples in pharmacokinetic study of an allopurinol formulation. The robustness and reproducibility of the bioanalytical method was reaffirmed through incurred sample reanalysis (ISR).

Underlying Mechanisms of Allopurinol in Eliminating Renal Toxicity Induced by Melamine-Uric Acid Complex Formation: A Computational Study

Using molecular dynamics, we address uric acid (UA) replacement by a model small-molecule inhibitor, allopurinol (AP), from its aggregated cluster in a columnar fashion. Experimentally it has been affirmed that AP is efficient in preventing UA-mediated renal stone formation. However, no study has presented the underlying mechanisms yet. Hence, a theoretical approach is presented for mapping the AP, which binds to melamine (MM) and UA clusters. In AP's presence, the higher-order cluster of UA molecules turns into a lower-order cluster, which "drags" fewer MM to them. Consequently, the MM-UA composite structure gets reduced. It is worth noting that UA-AP and AP-MM hydrogen-bonding interactions often play an essential role in reducing the UA-MM cluster size. Interestingly, an AP around UA makes a pillar-like structure, confirmed by defining the point-plane distribution function. The decomposition of the preferential interaction by Kirkwood-Buff integral into different angles like 0°-30°, 30°-60°, and 60°-90° firmly establishes the phenomenon mentioned above. However, the structural order for such π-stacking interactions between AP and UA molecules is not hierarchical but rather more spontaneous. The driving force behind UA-AP-MM composite formation is the favorable complexation energy that can be inferred by computing pairwise binding free energies for all possible combinations. Performing enhanced sampling and quantum calculations further confirms the evidence for UA degradation.

A Brief Review of Analytical Methods for the Estimation of Allopurinol in Pharmaceutical Formulation and Biological Matrices

This review article represents the collection and discussion of various analytical methods available in the literature for the determination of allopurinol (ALLP) in pharmaceutical and biological samples consisting of HPLC, UV-visible method, near-IR spectroscopy, spectrofluorometry, capillary electrophoresis, polarography, voltammetry, and hyphenated techniques such as LC-MS, LC-MS/MS, UPLC-MS/MS, and GC-MS. The anticipated review provides details about the comparative utilization of various analytical techniques for the determination of ALLP. The present review article can be effectively explored to conduct future analytical investigation for the estimation of ALLP.

A novel quality by design approach for development and validation of a green reversed-phase HPLC method with fluorescence detection for the simultaneous determination of lesinurad, febuxostat, and diflunisal: Application to human plasma

A novel and eco-friendly reversed-phase HPLC method with fluorescence detection was developed for simultaneous estimation of two co-administered antigout drugs (lesinurad and febuxostat) with diflunisal as a nonsteroidal anti-inflammatory drug. Unlike routine methodology, the developed method was optimized using analytical quality by design approach. A full factorial design was applied to optimize the effect of variable factors on chromatographic responses. The chromatographic separation was performed using isocratic elution on the Hypersil BDS C18 column at 40°C. The mobile phase consisted of acetonitrile:potassium phosphate buffer (30.0 mM; pH 5.5, 32.2:67.8% v/v) pumped at a flow rate of 1.0 mL/min and injection volume of 20.0 μL was employed. The proposed method was able to separate the ternary mixture in <10 min. The calibration curves of diflunisal, lesinurad, and febuxostat were linear over concentration ranges of 50.0-500.0, 50.0-700.0, and 20.0-700.0 ng/mL, respectively. Recovery percentages ranging from 98.1 to 101.3% with % relative standard deviation of <2% were obtained upon spiking to human plasma samples, indicating high bioanalytical applicability. Furthermore, the method was found to be excellent green when it was assessed according to Green Analytical Procedure Index and analytical Eco-Scale guidelines.

Micelle-Enhanced conventional and synchronous spectrofluorimetric methods for the simultaneous determination of lesinurad and febuxostat: Application to human plasma

A simple synchronous spectrofluorimetric method was developed for simultaneous determination of lesinurad and febuxostat. The investigated drugs were measured at 294 and 329 nm, respectively in the presence of each other without interference at Δλ of 50 nm (Method I). The different experimental parameters affecting the fluorescence intensities were carefully studied and optimized. The maximum synchronous fluorescence intensities were obtained at pH 6.5 using borate buffer and distilled water was used as a diluting solvent. Excellent linearity ranges were obtained using 20.0-500.0 ng mL^-1 and 1.0-80.0 ng mL^-1 for lesinurad and febuxostat, respectively. The method exhibited high sensitivity with detection limits down to 4.0 ng mL^-1 and 0.01 ng mL^-1 and quantitation limits down to 12.12 ng mL^-1 and 0.02 ng mL^-1, respectively. Recovery percentages ranged from 97.68 to 103.37% were obtained upon spiking of human plasma samples, indicating high bioanalytical applicability. Concerning Method II, methanolic solution of lesinurad was measured spectroflourimetrically with λ_excitation at 290 nm and λ_emission at 341 nm with high sensitivity using borate buffer of pH 6.5 and methanol as a diluting solvent. A considerable enhancement of the fluorescence intensity was achieved by using 1.0% w/v cetremide as a micellar system. The method was rectilinear over the concentration range of 3.0-80.0 ng mL^-1 with detection and quantitation limits down to 0.47 and 1.42 ng mL^-1, respectively. The developed method was efficiently applied for the estimation of the cited drug in spiked human plasma with high recovery percentages (98.58-101.64%). The methods were validated according to the ICH guidelines and further applied to commercial tablets with good results.

Spectrophotometric determination of lesinurad and allopurinol in recently approved FDA pharmaceutical preparation

Different spectrophotometic quantitative analytical methods have been developed and applied for quantitative determination of lesinurad and allopurinol in their newly FDA approved pharmaceutical dosage form. lesinurad was quantitatively analyzed based on its unique UV spectra without any mathematical processing step. Direct quantitative analysis was done through its recorded zero-order absorption spectra at 290 nm without any contribution from allopurinol. On the other hand two processing mathematical spectrophotometric methods were applied to enable quantitative analysis of allopurinol through resolving of the recorded overlapping UV spectra between lesinurad and allopurinol. Ratio difference and ratio derivative spectra manipulated methods were enabled successful quantitative determination of allopurinol without any contribution from lesinurad. The described methods were successfully applied for the quantitative analysis of the two drugs in Duzallo ® pharmaceutical dosage form.

Application of different spectrofluorimetric methods for determination of lesinurad and allopurinol in pharmaceutical preparation and human plasma

Lesinurad and allopurinol combination is newly FDA approved for treatment of patients suffering from hyperuricemia associated with uncontrolled gout. In the present work, two different highly sensitive, selective and accurate fluorescence spectroscopic methods were developed for quantitative analysis of lesinurad and allopurinol in their pharmaceutical dosage form without any tedious operation procedure. Lesinurad was quantitatively analyzed based on its unique native fluorescence nature. Lesinurad fluorescence emission was quantitatively determined at 343 nm after excitation at 288 nm without any interference from allopurinol. Allopurinol, has free terminal secondary amino group, reacted with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBDCl) through nucleophilic substitution mechanism forming highly fluorescent dark yellow fluorophore. Allopurinol was quantitavely analyzed based on measurement the emission fluorescence intensity of the fluorescent dark yellow fluorophore at 535 nm after excitation at 465 nm. Different parameters which affect the described methods of the studied drugs were carefully checked and optimized. Calibration graphs were found to be linear over the concentration range of 0.25-4.0 μg/mL for lesinurad and 0.2-20 μg/mL for allopurinol. The proposed methods were successfully applied for the quantitative analysis of the two drugs in Duzallo® pharmaceutical dosage form and spiked human plasma.