Fast separation and quantification of three anti-glaucoma drugs by high-performance liquid chromatography UV detection

An electrochemical sensor based on molecularly imprinted poly(o-phenylenediamine) for the detection of thymol

A molecularly imprinted electrochemical sensor was facilely fabricated for the detection of thymol (THY). o-Phenylenediamine (oPD) was used as the functional monomer and electropolymerized on the surface of the glassy carbon electrode (GCE) by using THY as the templates. After the THY templates were removed with 50 % (v/v) ethanol, imprinted cavities complementary to the templates were formed within the poly(o-phenylenediamine) (PoPD) films. The resultant molecularly imprinted PoPD/GCE (MI-PoPD/GCE) was used for the detection of THY, and a wide linear range from 0.5 to 100 μM with a low limit of detection (LOD) of 0.084 μM were obtained under the optimal conditions. The developed MI-PoPD/GCE also displays high selectivity, reproducibility and stability for THY detection. Finally, the content of THY in the real samples was accurately determined by the as-fabricated MI-PoPD/GCE, demonstrating its high practicability and reliability.

Interaction-Based Perspective for Designing Polymer Biomaterial: A Strategic Approach to the Chitosan-Glycerophosphate System

The conventional approach for developing any polymeric biomaterial is to follow protocols available in the literature and/or perform trial-and-error runs without a scientific basis. Here, we propose an analysis of a complex overlay of molecular interactions between drugs and polymers that provides a strategic pathway for biomaterial development. First, this work provides an innovative interaction-based method for developing an ocular formulation involving in situ gelling chitosan, gelatin, and glycerophosphate systems. A systematic interaction study is conducted based on the measurement of hydrodynamic radius, zeta potential, and viscosity with the sequential addition of formulation components. The increase in the hydrodynamic radius of the polymer with the addition of drugs can be interpreted as better diffusion of the drug inside the charged polymer chains and vice versa. Based on the knowledge of these interactions, a formulation has been designed that shows better drug release results with extended and sustained release compared to literature protocols, hence accentuating the importance of this study. An in-depth analysis of interactions can lead to a better understanding of the system. Second, we demonstrate the development of two dual-drug biomaterial systems, i.e., an in situ gelling and a liquid formulation at ocular surface temperature from the same polymers, which can be used as an ocular antiglaucoma formulation. Prior knowledge of the interactions between the drug polymers can be used to design a better formulation. The demonstrated application of this interaction-based protocol development can be extended universally to any biomaterial. This would provide a comprehensive idea about the properties and interactions of polymers and drugs, which can also serve as a base/starting point for a new formulation/biomaterial development.

Trends in development and quality assessment of pharmaceutical formulations - F2α analogues in the glaucoma treatment

The ocular delivery route presents a number of challenges in terms of drug administration and bioavailability. The low bioavailability following topical ophthalmic administration shows that there is a clear need for in-depth research aimed at finding both more efficacious molecules and formulations precisely targeted at the site of action. Continuous technological development will eventually result in improved bioavailability, lower dosages, reduced toxicity, fewer adverse effects, and thus better patient compliance and treatment efficacy. Technological development, as well as increasingly stringent quality requirements, help stimulate analytical progress. This is also clearly evident in the case of medicinal products used in the treatment of glaucoma, which are the subject of this review. Impurity profiling of PGF2α analogues, either in the pure substance or in the finished formulation, is a crucial step in assessing their quality. The development of specific, accurate and precise stability-indicating analytical methods for determining the content and related substances seems to be an important issue in relation to this tasks. A total of 27 official and in-house analytical methods are presented that are used for the analysis of latanoprost, travoprost and bimatoprost. The conditions for chromatographic separation with UV or MS/MS detection and the available results obtained during method validation are described. In addition, several aspects are discussed, with particular emphasis on the instability of the analogues in aqueous solution and the phenomenon of isomerism, which affects a potentially large number of degradation products.

Brimonidine

Brimonidine is a highly selective 2-adrenoceptor agonist that lowers intraocular pressure (IOP) by decreasing aqueous humor production and increasing aqueous humor outflow via the uveoscleral route. Brimonidine is used to treat glaucoma and other eye conditions. Brimonidine is a topical medication that is used mainly to treat open-angle glaucoma and ocular hypertension in the eyelids. The purpose of this chapter is to provide a comprehensive discussion of Brimonidine's nomenclature, physiochemical properties, preparation methods, identification procedures, and numerous qualitative and quantitative analytical techniques, as well as its ADME profiles and pharmacological effects. In addition, the chapter contains numerous approaches for separating brimonidine from other medications in combination formulations utilizing chromatographic techniques and other spectroscopic approaches.

Green HPLC method with time programming for the determination of the co-formulated eye drops of tafluprost and timolol in their challengeable ratio

A new, simple and selective HPLC method was implemented for the simultaneous estimation of tafluprost (TFL) and timolol (TIM) in their new anti-glaucoma combination in the challengeable ratio of 3 and 1000 for TFL and TIM, respectively. Separation was achieved using a BDS Hypersil phenyl column and a mobile phase made up of acetonitrile: 0.015 M phosphate buffer (50:50 v/v, pH 3.5) delivered at 1 mL min⁻¹ and the separation was completed in less than 6 min. UV detection was time programmed at 220 nm for the first 4.5 min and later at 254 nm. Mebeverine (MEB) was used as an internal standard (I.S.). The linearity was observed in the ranges of 0.6–45 and 50–2000 µg mL⁻¹ with limits of detection (LOD) of 0.18, 16.48 µg mL⁻¹ and limits of quantification (LOQ) of 0.55, 49.94 µg mL⁻¹ for TFL and TIM, respectively. The method satisfied International Council for Harmonization (ICH) validation guidelines. The study was extended to the estimation of the studied drugs in their co-formulated eye drops as well as in their single dosage forms with acceptable percentage recoveries. Moreover, Green Analytical Procedure Index (GAPI) and analytical Eco-scale were investigated to confirm the greenness of the proposed HPLC method.

Full Factorial Design for Development and Validation of a Stability-Indicating RP-HPLC Method for the Estimation of Timolol Maleate in Surfactant-Based Elastic Nano-Vesicular Systems

A novel isocratic stability-indicating chromatographic method was developed, optimized and validated using Design-Expert® following ICH guidelines for the quantification of Timolol maleate (TM). The intrinsic stability of TM was assessed by force degradation studies, which concluded no extensive degradation except under alkaline and oxidative conditions. TM was quantified accurately in the surfactant-based elastic vesicular system by separating it on Hypersil BDS C8 column using triethylamine in H2O (0.15%v/v; pH 3.0) and acetonitrile (ACN; 65:35%v/v). The influence of variable factors like mobile phase pH, injection volume (μL), flow rate (mL/min) and ACN content (%) on method responses were assessed using a full factorial design. The method was linear between 0.05 and 10 μg/mL with an R2 value of 0.9993. Limit of detection and limit of quantification were found to be 0.90 and 27.2 ng/mL. The method was specific, with recovery in plain drug solution of 89-92% and elastic nanovesicles of 90-93%. The experimental model was significant (P < 0.0001) as indicated by deliberate changes in the method analyzed through analysis of variance. The total drug content in elastic nanovesicles was estimated to be 9.53 ± 0.01 mg/20-mL dispersion and entrapment efficiency was 44.52 ± 0.73%. The developed method was rapid, economic and precise for the quantification of TM in bulk and vesicular system.

Latanoprost Quantification in Ocular Implants and Tissues: HPLC-Fluorescence vs HPLC-UV

Anti-glaucoma latanoprost-loaded ocular implants provide prolonged delivery and enhanced bioavailability relative to the conventional eye drops. This study aims at the development and validation of a reversed-phase high-performance liquid chromatography method for quantitative analysis of nanogram levels of latanoprost in the eye, and for the first time, compares the use of fluorescence vs ultraviolet (UV) detectors in latanoprost quantification. The mobile phase was composed of acetonitrile:0.1% v/v formic acid (60:40, v/v) with a flow rate of 1 mL/min and separation was done using a C18 column at temperature 40°C. The fluorescence excitation and emission wavelengths were set at 265 and 285 nm, respectively, while the UV absorption was measured at 200 nm. The latanoprost concentration-peak area relationship maintained its linearity (R2 = 0.9999) over concentration ranges of 0.063-10 μg/mL and 0.212-10 μg/mL for the fluorescence and UV detectors, respectively. The UV detector showed better precision, while the fluorescence detector exhibited higher robustness and greater sensitivity, with a detection limit of 0.021 μg/mL. The fluorescence detector was selected for quantification of latanoprost released from ocular implants in vitro and in porcine ocular tissues. The developed method is a robust, rapid and cost-effective alternative to liquid chromatography-mass spectrometry for routine analysis of latanoprost released from ocular implants.

Single quad mass analyzer coupled UPLC method for impurity profile of Brimonidine tartrate and Timolol maleate: Application in their binary mixture ophthalmic formulation

The main objective of the study is to develop a suitable and rapid UPLC/PDA method by coupling online to Quadrupole Dalton analyzer (QDa), a mass detector for the identification and impurity profiling of Brimonidine Tartrate (BRIM)/Timolol maleate (TIMO) in the ophthalmic formulation. Chromatographic separation was achieved on ethylene bridged hybrid octadecylsilane column having 1.7μm particle size in gradient mode using high pure heptafluorobutyric acid as a buffer (A) and water, methanol, and acetonitrile (B) as mobile phase with a flow rate of 0.3mlmin^-1. Based on the spectral maxima, BRIM and its impurities were monitored at 248nm, and TIMO and its impurities were monitored at 295nm. During evaluation of stress conditions and stability data unknown degradants are observed and identified as m/z 218.01 (DP1) and m/z 390.03 (DP2) using QDa-ESI+ scanning mode technique. The performance of the method was systematically validated according to ICH Q2 (R1) guidelines and the method shown very good sensitivity (≥0.5μg.mL^-1) and linearity (r²≥0.999) with consistent recoveries and less than 5% RSD for all compounds. Hence, the proposed UPLC/PDA/QDa method is a simple, sensitive and comprehensive technique where identification and quantification can be done. It gives for complete impurity profile evaluation of BRIM/TIMO in the ophthalmic formulation during quality control in the pharmaceutical industry.

Latanoprost-loaded phytantriol cubosomes for the treatment of glaucoma

Glaucoma is a degenerative optic neuropathy characterized by increased intraocular pressure that if untreated can result in blindness. Ophthalmological drug therapy is a challenge of great clinical importance due to the diversity of ocular biological barriers which commonly causes limited or no effectiveness for drugs delivered through the eye. In this work, we proposed the development of nanosized cubic liquid crystals (cubosomes) as a new drug carrier system for latanoprost, an anti-glaucoma drug. Latanoprost-loaded phytantriol cubosomes (CubLnp) were prepared using a top-down method. Latanoprost concentration in the formulations ranged from 0.00125% to 0.02% w/v. All cubosomes displayed an average size around 200 nm, a low polydispersity index of 0.1 and zeta potential values around -25 mV, with an encapsulation efficiency of about 90%. Structural studies revealed that cubosomes displayed a double-diamond surface, Pn3m cubic-phase structure, and was not affected by drug loading. Calorimetric studies revealed a fast and exothermic interaction between latanoprost and cubosomes. According to in vitro essays, latanoprost release from cubosomes was slow in time, evidencing a sustained release profile. Based on this behavior, the in vivo hypotensive intraocular effect was evaluated by means of the subconjunctival administration of CubLnp in normotensive rabbits. We obtained promising results in comparison with a marketed latanoprost formulation (0.005% w/v).

Simultaneous spectrofluorometric analysis of tablets containing hydrochlorothiazide combined with timolol maleate or amiloride hydrochloride

Green and sensitive spectrofluorometric methods have been developed and validated for the determination of timolol maleate (TML)/hydrochlorothiazide (HCT) and amiloride hydrochloride (AMH)/hydrochlorothiazide in tablets. The proposed spectrofluorometric procedures were found to be linear in the range of 4-12, 5-35 and 0.025-0.2 mg L-1 for HCT, TML and AMH, resp. The excitation and emission wavelengths for HCT, TML and AMH at room temperature were 270 and 375, 295 and 435, 330 and 415 nm, resp. The methods were validated with respect to ICH guidelines. The AMH showed higher sensitivity with lower values of LOD and LOQ values compared to HCT and TML. The proposed methods were applied to two pharmaceutical formulations; the method for HCT and AMH has proven as reliable assaying method, whereas the method for TML, when combined with HCT, is applicable to screening semi-quantitative analyses.

Colorimetric determination of Timolol concentration based on localized surface plasmon resonance of silver nanoparticles

In this work, a rapid and simple colorimetric method based on the surface plasmon resonance of silver nanoparticles (AgNPs) was developed for the detection of the drug Timolol. The method used is based on the interaction of Timolol with the surface of the as-synthesized AgNPs, which promotes aggregation of the nanoparticles. This aggregation exploits the surface plasmon resonance through the electric dipole-dipole interaction and coupling among the agglomerated particles, hence bringing forth distinctive changes in the spectra as well as the color of colloidal silver. UV-vis spectrophotometery was used to monitor the changes of the localized surface plasmon resonance of AgNPs at wavelengths of 400 and 550 nm. The developed colorimetric sensor has a wide dynamic range of 1.0 × 10(-7) M-1.0 × 10(-3) M for detection of Timolol with a low detection limit of 1.2 × 10(-6) M. The proposed method was successfully applied for the determination of Timolol concentration in ophthalmic eye-drop solution with a response time lower than 40 s.