Continuous potentiometric monitoring of viagra (sildenafil) in pharmaceutical preparations using novel membrane sensors

A Comprehensive Review on Analytical Techniques for Determination of Sex Stimulants, PDE5 Inhibitors in Different Matrices with Special Focus on the Electroanalytical Methods

Erectile dysfunction (ED) is one of the most common chronic diseases affecting men and its incidence increases with aging. Due to its substantial influence on the quality of life, phosphodiesterase type-5 (PDE5) inhibitors have been implemented to treat ED by increasing the penile blood flow that results in improving erection. PDE5 inhibitors is a class of drugs that affects many pharmacological sectors, and it is essential to review the different analytical methods described for their determination. Few reviews were published concerning this group of drugs. For this reason, this review article gathers the different analytical methods used to determine PDE5 inhibitors in pharmaceutical and biological samples over the past 20 years. Different analytical techniques were used to analyze these compounds in different matrices such as separation methods (capillary electrophoresis, LC-MS, UPLC-MS/MS, and GC-MS), spectroscopic methods (UV-visible methods, FT-IR spectroscopy and spectrofluorometry) and electrochemical methods (polarography, voltammetry and potentiometry). This review focuses on the different electrochemical methods and their use in analytical determination of PDE5 inhibitors in pharmaceutical dosage forms and biological samples. Moreover, it discusses the different modified electrodes used for their electroanalytical determination and the behavior of the studied drugs at different modified electrodes. Additionally, this review discusses the pharmacokinetics of the studied compounds and their interactions with other co-administered drugs especially the metabolic interactions between the studied compounds and other co-administered drugs in different matrices. This literature survey would provide a beneficial guide for future analytical investigation of PDE5 inhibitors.

Two Versatile Pencil Graphite-Polymer Sensor Electrodes Coupled with Potentiometry and Potentiometric Titration Methods: Profiling Determinations of Vitamin V in Tablets and Urine Samples

Herein, we developed a new pencil graphite ion-selective electrode strategy for the broadly used erectile dysfunction medication, sildenafil citrate (SC, vitamin V), for its automated potentiometry and potentiometric titration profiling in marketed tablets and human urine samples. The method was based on ion-pair complexation between SC and sodium tetraphenylborate (Na-TPB) or phosphotungstic acid (PTA), embedded into a pencil-fabricated graphite sensor electrode coated with poly(vinyl chloride, PVC) matrix, which is pre-plasticized with two different pre-studied plasticizers. The modern fabricated electrodes have a proven fast near-Nernstian response for SC over the concentration range of 1.0 × 10^-6 to 1.0 × 10^-2 and 1.0 × 10^-5 to 1.0 × 10^-2 M, with LODs of 6.5 × 10^-7 and 5.5 × 10^-6 over a pH 3-6 for (SC-TPB)- and (SC-PTA)-based membrane sensors, of O-nitrophenyl octyl ether (O-NPOE) and dioctyl phthalate (DOP), respectively. The selectivity coefficients for different interferents, including many inorganic cations, sugars, and/or nitrogenous compounds, were tested and confirmed. Applications of the proposed method were conducted on the determination of SC in its tablets and urine samples under the proper conditions. The percent recovery values were compared with those obtained by an official method and showed an RSD ≤ 0.3% (n = 5).

Sildenafil 4.0-Integrated Synthetic Chemistry, Formulation and Analytical Strategies Effecting Immense Therapeutic and Societal Impact in the Fourth Industrial Era

Sildenafil is a potent selective, reversible inhibitor of phosphodiesterase type 5 (PDE5) approved for the treatment of erectile dysfunction and pulmonary arterial hypertension. Whilst twenty years have passed since its original approval by the US Food and Drug Administration (USFDA), sildenafil enters the fourth industrial era catalyzing the treatment advances against erectile dysfunction and pulmonary hypertension. The plethora of detailed clinical data accumulated and the two sildenafil analogues marketed, namely tadalafil and vardenafil, signify the relevant therapeutic and commercial achievements. The pharmacokinetic and pharmacodynamic behavior of the drug appears complex, interdependent and of critical importance whereas the treatment of special population cohorts is considered. The diversity of the available formulation strategies and their compatible administration routes, extend from tablets to bolus suspensions and from per os to intravenous, respectively, inheriting the associated strengths and weaknesses. In this comprehensive review, we attempt to elucidate the multi-disciplinary elements spanning the knowledge fields of chemical synthesis, physicochemical properties, pharmacology, clinical applications, biopharmaceutical profile, formulation approaches for different routes of administration and analytical strategies, currently employed to guide the development of sildenafil-based compositions.

Novel Aminoacridine Sensors Based on Molecularly Imprinted Hybrid Polymeric Membranes for Static and Hydrodynamic Drug Quality Control Monitoring

Novel biomimetic potentiometric ion-selective electrodes (ISEs) were fabricated and designed for the assessment of aminoacridine (ACR) based on newly synthesized imprinted polymer (MIP) membranes. Thermal polymerization of methacrylic acid (MAA) or acrylamide (AM) as function monomer, aminoacridine as a template and ethylene glycol dimethacrylate (EGDMA) as across-linker, were utilizedto give the molecular recognition part. The membranes of sensors I andII consist of MIP based MAA and AM, respectively, dispersed in a poly(vinyl chloride) membrane plasticized with dioctyl phthalate (DOP) in the ratio of 3.0 wt%, 32.2 wt% and 64.8 wt%, respectively. Sensors III and IV were similarly prepared with added 1.0 wt% tetraphenyl borate (TPB⁻) as an anionic discriminator. Sensors I and II exhibited near-Nernstian potential response to ACR⁺ with slopes of 51.2 ± 1.3 and 50.5 ± 1.4 mV/decade in a 0.01 M phosphate buffer of pH 6.0. The linear response coversthe concentration range of 5.2 × 10⁻⁶ to 1.0 × 10⁻³ M with a detection limit of 0.05 and 0.17 μg/mL for sensors I and II, respectively. The performance characteristics of these sensors were evaluated under static and hydrodynamic mode of operations. They were used for quality control assessment of aminoacridine in some pharmaceutical preparations and biological samples.

Non-Equilibrium Potential Responses towards Neutral Orcinol Using All-Solid-State Potentiometric Sensors Integrated with Molecularly Imprinted Polymers

Molecularly imprinted polymer (MIP) receptors have been synthesized, characterized, and applied as new selective receptors in solid-contact ion selective electrodes (ISEs) towards non-dissociated 3,5-dihydroxytoluene (orcinol). Two monomers, namely methacrylic acid (MAA) and acrylamide (AA), were used in the preparation of MIP receptors. Graphene (Gr) was used as the solid contact material between the sensing membrane and the electrical contact substrate. Based on non-equilibrium sensing mechanism, the proposed sensors reveal observably enhanced detection sensitivity towards orcinol with detection limits 1.7 × 10⁻⁵ and 3.3 × 10⁻⁶ M for sensors based on MIP/MAA and MIP/AA, respectively. The selectivity coefficients measured by the modified separate solution method (MSSM) for the proposed sensors showed good selectivity towards orcinol over most common other phenols and inorganic anions. All measurements were made in the presence of 30 mM phosphate buffer solution (PBS) with a pH of 7.0. Potential stability for the proposed sensors was tested by constant-current chronopotentiometry. No water films were formed between the sensing membrane and the electron conductor substrate. The applicability of MIP/MAA incorporated ISE has been checked by recovery test of orcinol in the presence of soil matrix and by standard addition method.

Conventional and planar chip sensors for potentiometric assay of uric acid in biological fluids using flow injection analysis

The potentiometric response properties of several PVC-based membrane sensors using phthalocyanine complexes of cobalt(II) (CoPC) and Fe(II) (FePC) as anion carriers, towards uric acid were constructed and characterized. The sensors demonstrated fast near-Nernstian response for uric acid over the concentration ranges 9.1 x 10(-6) to 9.1 x 10(-2) and 3.1 x 10(-5) to 3.1 x 10(-2)M with detection limits 0.67 and 2.85 microg mL(-1) over pH 6.5-8 for CoPC and FePC based membrane sensors plasticized with o-NPOE and 1% TDMAC, respectively. A novel solid-state planar chip urate sensor was developed, characterized according to IUPAC recommendations, easily used in a single channel wall-jet flow injection system and compared with a tubular detector. The intrinsic characteristics of the detectors in a low dispersion manifold were determined and compared with data obtained under hydrodynamic mode of operation. Validation of the assay methods with the proposed sensors by measuring the lower limit, range, accuracy, precision, repeatability and between-day-variability revealed good performance characteristics confirming applicability for continuous determination of uric acid. The sensors were used for determining urate in biological fluids at an input rate of 50 samples per hour. The results compare favorably with data obtained by the standard spectrophotometry.