A Stability-Indicating LC Method for Candesartan Cilexetil

An isocratic reversed-phase liquid chromatographic method has been developed for quantitative determination of candesartan cilexetil, used to treat hypertension, in the bulk drug and in pharmaceutical dosage forms. The method is also applicable to analysis of related substances. Chromatographic separation was achieved on a 250 mm × 4.6 mm, 5 μm particle, CN column with a 50:50 (v/v) mixture of phosphate buffer, pH 3.0, and acetonitrile as mobile phase. The flow rate was 1.0 mL min⁻¹ and the detection wavelength was 210 nm. Resolution of candesartan cilexetil and six potential impurities was greater than 2.0 for all pairs of compounds. The drug was subjected to hydrolytic, oxidative, photolytic, and thermal stress and substantial degradation occurred in alkaline and acidic media and under oxidative and hydrolytic stress conditions. The major product obtained as a result of basic hydrolysis was different from that produced by acid hydrolysis and aqueous hydrolysis. The stress samples were assayed against a reference standard and the mass balance was found to be close to 99.6%. The method was validated for linearity, accuracy, precision, and robustness.     

Two selective HPTLC methods for determination of some angiotensin II receptor antagonists in tablets and biological fluids

Two simple, selective, precise and highly sensitive high‐performance thin‐layer chromatography (HPTLC) methods have been developed and validated for analysis of five angiotensin II receptor antagonists, namely losartan, irbesartan valsartan, candesartan and olmesartan, which are widely used in clinical practice. HPTLC of the drugs was performed on pre‐coated silica gel HPTLC plates 60 F₂₅₄ by development using a mobile phase composed of chloroform–acetone–glacial acetic acid (7.8:1.5:0.7m v/v/v), which was suitable for all of the studied drugs. The first method depended on utilizing reflectance/fluorescence mode for detection while the second method depended on using 2,3,5,6‐tetrachloro‐1,4‐benzoquinone as spraying reagent for the first time to form orange spots scanned at 460 nm. A good linear relationship was obtained over the concentration ranges of 1.2–60 and 360–3000 ng/band while detection and quantification limits were in the ranges of 0.07–0.43, 45.2–140.49 and 0.21–1.29, 137.05–425.74 ng/band for reflectance/fluorescence and reflectance/absorbance methods respectively. The developed methods were applied successfully for their determination in tablets and spiked human plasma for reflectance/fluorescence method with good accuracy and precision, and so can be applied in the pharmacokinetic and bioavailability studies.     

Simultaneous quantification of candesartan and irbesartan in rabbit eye tissues by liquid chromatography–tandem mass spectrometry

Diabetic retinopathy is a major cause of vision loss in adults. Novel eye-drop formulations of candesartan and irbesartan are being developed for its cure or treatment. To support a preclinical trial in rabbits, it was critical to develop and validate a new LC–MS/MS method for simultaneous quantification of candesartan and irbesartan in rabbit eye tissues (cornea, aqueous humor, vitreous body and retina/choroid). Eye tissue samples were first homogenized in H₂O-diluted rabbit plasma. The candesartan and irbesartan in the supernatants together with their respective internal standards (candesartan-d₄ and irbesartan-d₄) were extracted by solid-phase extraction. The extracted samples were injected onto a C₁₈ column for gradient separation. The MS detection was in the positive electrospray ionization mode using the multiple reaction monitoring transitions of m/z 441 → 263, 445 → 267, 429 → 207, and 433 → 211 for candesartan, candesartan-d₄, irbesartan and irbesartan-d₄, respectively. For the validated concentration ranges (2–2000 and 5–5000 ng/g for candesartan and irbesartan, respectively), the within-run and between-run accuracies (% bias) were within the range of −8.0–10.0. The percentage CV ranged from 0.6 to 7.3. There was no significant matrix interference nor matrix effect from different eye tissues and different rabbits. The validated method was successfully used in the Good Laboratory Practice (GLP) study of rabbits.     

Determination of Candesartan Cilexetil in Tablet Dosage Forms and Dissolution Testing Samples by First Derivative UV Spectrophotometric Method

Abstract

This article describes the development and validation of a first derivative UV quantitative analytical method for determination of candesartan cilexetil in tablet dosage forms. A signal at 270.1 nm of the first derivative spectrum (ID_270.1) was found adequate for quantification. The limit of quantification was 3.06 µg/ml. The linearity between ID_270.1 nm and concentration of candesartan cilexetil in the range of 6.00–32.00 µg/ml presented a correlation coefficient of (r²) = 0.9990. The mean recovery percentage was 100.97 and 99.23% for candesartan cilexetil standard solution and candesartan standard cilexetil solution with excipients, respectively. The intraday and interday accuracy of the assay was 98.60% and 99.10% respectively. The intraday and interday variability was below 2.0%.

The proposed method is accurate, precise, sensitive, and selective and can be used in quality control laboratories for its intended purpose.     

Secondary Effects of Hypochlorite Treatment on the Emerging Pollutant Candesartan: The Formation of Degradation Byproducts and Their Toxicological Profiles

In recent years, many studies have reported the frequent detection of antihypertensive agents such as sartans (olmesartan, valsartan, irbesartan and candesartan) in the influents and effluents of wastewater treatment plants (WWTPs) and in the superficial waters of rivers and lakes in both Europe and North America. In this paper, the degradation pathway for candesartan (CAN) was investigated by simulating the chlorination process that is normally used to reduce microbial contamination in a WWTP. Twelve isolated degradation byproducts (DPs), four of which were isolated for the first time, were separated on a C-18 column by employing a gradient HPLC method, and their structures were identified by combining nuclear magnetic resonance and mass spectrometry and comparing the results with commercial standards. On the basis of these results, a mechanism of formation starting from the parent drug is proposed. The ecotoxicity of CAN and its DPs was studied by conducting a battery of ecotoxicity tests; bioassays were performed using Aliivibrio fischeri (bacterium), Daphnia magna (planktonic crustacean) and Raphidocelis subcapitata (alga). The ecotoxicity results shed new light on the increased toxicity of DPs compared with the parent compound.     

Physicochemical Profiling of Sartans: A Detailed Study of Ionization Constants and Distribution Coefficients

A detailed investigation of the ionization and lipophilicity profiles of selected sartans (valsartan, losartan, irbesartan, candesartan, candesartan cilexetil), a class of antihypertensives commonly used in therapy, is presented. The pK_a macroconstants were determined by integrated potentiometry, capillary electrophoresis, and UV spectrophotometry. The measured pK_a macroconstants were connected with the ionizable centers present in each molecule with the aid of model compounds. Potentiometric titrations with the GLpKa apparatus were performed to determine the distribution profile (log D vs. pH) of valsartan, while the shake‐flask procedure was used to characterize the distribution profile of the other compounds. Valsartan showed a lipophilicity profile consistent with the presence of two acidic centers. Losartan and irbesartan, which contain one acidic and one basic center, displayed the classical bell‐shaped profile of ordinary ampholytes. By contrast, a more complex situation emerged in the case of candesartan, due to the large number of ionization equilibria involved. The low solubility of candesartan cilexetil, together with the ease of hydrolysis of the ester moiety, prevented a successful investigation of its ionization and lipophilicity profiles.     

A simple,rapid and fully validated HPLC method for simultaneous quantitative bio‐analysis of rosuvastatin and candesartan in rat plasma: Application to pharmacokinetic interaction study

A simple, precise and accurate HPLC method was developed, optimized and validated for simultaneous determination of rosuvastatin and candesartan in rat plasma using atorvastatin as an internal standard. Solid‐phase extraction was used for sample cleanup and its subsequent optimization was carried out to achieve higher extraction efficiency and to eliminate matrix effect. A quality by design approach was used, wherein three‐level factorial design was applied for optimization of mobile phase composition and for assessing the effect of pH of the mobile phase using Design Expert Software. Adequate separation for both analytes was achieved with a Waters C₁₈ column (250 × 4.6 mm, 5 μm) using acetonitrile–5 mm sodium acetate buffer (70:30, v/v; pH adjusted to 3.5 with acetic acid) as a mobile phase at a flow rate of 1.0 mL/min and wavelength of 254 nm. The calibration curves were linear over the concentration ranges 5–150 and 10–300 ng/mL for rosuvastatin (ROS) and candesartan (CAN), respectively. The validated method was successfully applied to a pharmacokinetic study in Wistar rats and the data did not reveal any evidence for a potential drug–drug interaction between ROS and CAN. This information provides evidence for clinical rational use of ROS and CAN.     

The simultaneous UPLC–MS/MS determination of emerging drug combination; candesartan and chlorthalidone in human plasma and its application

A novel, precise, sensitive and accurate ultra‐performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) method has been developed for the simultaneous determination of a novel drug combination, candesartan (CAN) and chlorthalidone (CHL), in human plasma. Chromatographic separation was achieved on Waters Acquity UPLC BEH C₁₈ (50 × 2.1 mm, 1.7 μm). Mobile phase consisting of 1 mm ammonium acetate in water–acetonitrile (20:80 v /v) was used. The total chromatographic runtime was 1.9 min with retention times for CAN and CHL at 0.7 and 1.1 min respectively. Ionization and detection of analytes and internal standards was performed on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring and negative ionization mode. Quantitation was done to monitor protonated precursor → product ion transition of m /z 439.2 → 309.0 for CAN, 337.0 → 189.8 for CHL and 443.2 → 312.1 for candesartan D4 and 341.0 → 189.8 for chlorthalidone D4. The method was validated over a wide dynamic concentration range of 2.0–540.0 ng/mL for candesartan and 1.0–180.0 ng/mL for chlorthalidone. The validated method was successfully applied for the assay of CAN and CHL in healthy volunteers.     

A novel and practical synthesis of substituted 2-ethoxy benzimidazole: candesartan cilexetil

A novel and practical synthetic route for the preparation of candesartan cilexetil from methyl 2-amino-3-nitrobenzoate is described. The key steps are the reaction of methyl 2-bromo-3-(diethoxymethyleneamino)benzoate with (2′-(1-trityl-1H-tetrazol-5-yl) biphenyl-4-yl) methanamine and the final formation of 2-ethoxy benzimidazole ring via intramolecular N-arylation. The final ring closure process could be utilized to prepare other 2-substituted benzimidazoles. The method is simple for operation and suitable for industrial production.     

S-2-甲氧基环己酮的合成研究

优化了S-2-甲氧基环己酮的合成方法, 该合成路线产率高、成本低、适合于生产; 并利用S-2-甲氧基环己酮合成了用于制备新一类β-内酰胺类抗生素sanfetrinem cilexetil 的关键中间体2.