The recommended method for the biopharmaceutical evaluation of drug solubility is the shake flask; however, there are discrepancies reported about the solubility of certain compounds measured with this method, one of them is candesartan cilexetil. The present work aimed to elucidate the solubility of candesartan cilexetil by associating others assays such as stability determination, polymorphic characterization and in silico calculations of intrinsic solubility, ionized species, and electronic structures using quantum chemistry descriptors (frontier molecular orbitals and Fukui functions). For the complete biopharmaceutical classification, we also reviewed the permeability data available. The polymorphic form used was previously identified as the form I of candesartan cilexetil. The solubility was evaluated in biorelevant media in the pH range of 1.2-6.8 at 37.0°C according to the stability previously assessed. The solubility of candesartan cilexetil is pH dependent and the dose/solubility ratios obtained demonstrated the low solubility of the prodrug. The in silico calculations supported the found results and evidenced the main groups involved in the solvation, benzimidazole, and tetrazol-biphenyl. The human absolute bioavailability reported demonstrates that candesartan cilexetil has low permeability and when associated with the low solubility allows to classify it as class 4 of the Biopharmaceutics Classification System.

In the current study, a novel three-dimensional macroporous hydroxyapatite/ chitosan foam (HA/CS)-supported polymer micelle (PM/HA/CS) was developed, and its potential as an oral drug delivery system to enhance the solubility and oral bioavailability of poorly soluble compounds was systemically studied. Candesartan cilexetil (CC) was selected as a poorly soluble model drug. Firstly, HA/CS foam was synthesized using a wet chemical co-precipitation approach and poly-(methyl methacrylate) colloidal crystals as a macropore template. Subsequently, the CC-loaded polymer micelles were efficiently encapsulated into the macropores of the HA/CS foam and freeze-dried to produce powdery CC-loaded PM/HA/CS composites (CC-PM/HA/CS). The resulting CC-PM/HA/CS particles were then characterized in terms of porous structure, morphology, angle of repose, crystallinity, drug loading, dissolution profiles, and physical stability. Differential scanning calorimetry (DSC) analysis confirmed that CC-PM/HA/CS was present in an amorphous form and has an excellent physical stability. Under both simulated gastric and intestinal conditions, the aqueous solubility and dissolution rate of the PM/HA/CS-based CC formulation were significantly increased compared with the pure drug powder. In addition, PM/HA/CS is almost completely non-cytotoxic. The PM/HA/CS-based CC formulation produced approximately 1.9-fold increased bioavailability when compared to the marketed tablets (Blopress®) administered to fasted Sprague-Dawley rats. On the whole, PM/HA/CS benefits from the advantages of three dimensional macroporous HA/CS foam and polymer micelles, and exhibits great potential as a drug delivery system for increasing the solubility and oral bioavailability of a poorly soluble compound, like CC.

The ATP-binding cassette transporter ABCG2 (BCRP and MXR) is involved in the absorption, distribution, and elimination of numerous drugs. Thus, drugs that are able to reduce the activity of ABCG2, e.g., antihypertensive AT1 receptor antagonists (ARBs), may cause drug-drug interactions and compromise drug safety and efficacy. In addition, genetic variability within the ABCG2 gene may influence the ability of the transporter to interact with ARBs. Thus, the aim of this study was to characterize the ARB-ABCG2 interaction in the light of naturally occurring variations (F489L, R482G) or amino acid substitutions with in silico-predicted relevance for the ARB-ABCG2 interaction (Y469A; M483F; Y570A). For this purpose, ABCG2 variants were expressed in HEK293 cells and the impact of ARBs on ABCG2 activity was studied in vitro using the pheophorbide A (PhA) efflux assay. First, we demonstrated that both the F489L and the Y469A substitution, respectively, reduced ABCG2 protein levels in these cells. Moreover, both substitutions enhanced the inhibitory effect of candesartan cilexetil, irbesartan, losartan, and telmisartan on ABCG2-mediated PhA efflux, whereas the R482G substitution blunted the inhibitory effect of candesartan cilexetil and telmisartan in this regard. In contrast, the ARB-ABCG2 interaction was not altered in cells expressing either the M483F or the Y570A variant, respectively. In conclusion, our data indicate that the third transmembrane helix and adjacent regions of ABCG2 may be of major importance for the interaction of ARBs with the ABC transporter. Moreover, we conclude from our data that individuals carrying the F489L polymorphism may be at increased risk of developing ABCG2-related drug-drug interactions in multi-drug regimens involving ARBs.

In this study, the in vitro and in vivo interchangeability between generic candesartan 16 mg and the branded formulation was assessed. The in vitro release of these products was conducted in 3 pH media (1.2, 5.0, and 6.8), and similarity factors (f2) were calculated. This bioequivalence study was a randomized, 2-period crossover study that included 42 healthy adult male subjects under fasting conditions with a 9-day washout. The pharmacokinetic (PK) parameters AUC0-last , AUC0-∞ , and Cmax , tmax , and the elimination half-life time were assessed based on the plasma concentrations of candesartan, using a newly developed and validated liquid chromatography-tandem mass spectrometry bioanalytical method with acceptable degrees of linearity, sensitivity, precision, and accuracy. The geometric mean (ng·h/mL) of the AUC0-∞ for the test and brand was 1595.49 and 1620.54, respectively, and the Cmax (ng/mL) was 160.91 and 160.88, respectively. The 90%CIs of geometric mean ratios (test-to-reference ratios) were 98.26%, 98.45%, and 99.86% for AUC0-last , AUC0-∞ , and Cmax respectively. These PK parameters lie within the US Food and Drug Administration- and European Medicines Agency-specified bioequivalence limit (80%-125%). Both products were well tolerated by all the subjects. The tested drug product was bioequivalent to the reference drug and had the same safety profile.

New analytical methods have been developed and validated on high performance liquid chromatography (HPLC) to assess the assay, content uniformity and dissolution of immediate release candesartan cilexetil 32 mg tablets. Method development studies were performed on cyano column. Mobile phase of assay and content uniformity test consisted of mixture of 0.05 M phosphate buffer, pH 4.5 and methanol (40 : 60, v/v) adjusted to pH 4.0 with trifluoroacetic acid, whereas mobile phase of dissolution test consisted of mixture of I mM phosphate buffer and acetonitrile (50 : 50, v/v) adjusted to pH 2.0 with trifluoroacetic acid. Mobile phases were pumped at flow rate of 1.0 mL/min, ultraviolet-visible (UV) detector was operated at 254 nm, injection volume was set at 20 μL, column temperature was held at 25⁰C. Dissolution medium was 0.05 M phosphate buffer, pH 6.5 including 0.70% (w/v) polysorbate 20. Validation studies met acceptance criteria of system suitability, specificity, linearity and range, accuracy, precision, detection limit (LOD), quantitation limit (LOQ) and robustness parameters.

The World Health Organization has warned that substandard and falsified medical products (SFs) can harm patients and fail to treat the diseases for which they were intended, and they affect every region of the world, leading to loss of confidence in medicines, health-care providers, and health systems. Therefore, development of analytical procedures to detect SFs is extremely important. In this study, we investigated the quality of pharmaceutical tablets containing the antihypertensive candesartan cilexetil, collected in China, Indonesia, Japan, and Myanmar, using the Japanese pharmacopeial analytical procedures for quality control, together with principal component analysis (PCA) of Raman spectrum obtained with handheld Raman spectrometer. Some samples showed delayed dissolution and failed to meet the pharmacopeial specification, whereas others failed the assay test. These products appeared to be substandard. Principal component analysis showed that all Raman spectra could be explained in terms of two components: the amount of the active pharmaceutical ingredient and the kinds of excipients. Principal component analysis score plot indicated one substandard, and the falsified tablets have similar principal components in Raman spectra, in contrast to authentic products. The locations of samples within the PCA score plot varied according to the source country, suggesting that manufacturers in different countries use different excipients. Our results indicate that the handheld Raman device will be useful for detection of SFs in the field. Principal component analysis of that Raman data clarify the difference in chemical properties between good quality products and SFs that circulate in the Asian market.

Among the strategies to improve the biopharmaceutic properties of poorly soluble drugs, Supersaturating Drug Delivery Systems like polymer-based amorphous solid dispersions (SD) have been successfully applied. The screening of appropriate polymeric carriers to compose SD is a crucial point on their development. In this study, hydroxypropylmethylcellulose (HPMC), hydroxypropylmethylcellulose acetate succinate (HPMCAS) types L, M and H and polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft copolymer (SOL) were evaluated by in vitro supersaturation studies regarding their anti-precipitant ability on the poorly soluble drug candesartan cilexetil (CC) under two different media, including biorelevant conditions. According to the results, HPMCAS M was considered the best carrier to develop SD containing CC among all the polymers tested, due to its good anti-precipitant performance in both media. In addition, the medium used in the in vitro supersaturation studies played an important role on the results, and its selection should be carefully done.

Development, validation and comparison of two stability-indicating LC methods, one with photodiode array detector (DAD) and the other with evaporative light scattering detector (ELSD), were performed for simultaneous determination of candesartan cilexetil (CANC) and hydrochlorothiazide (HCTZ), in pharmaceutical samples. A RP-18 column (125 mm × 4 mm, 5 μm) was used for separation of CANC, HCTZ and its major degradation products, using acetonitrile and phosphate buffer (pH 6.0) for DAD method and acetonitrile and water with acetic acid and triethylamine (pH 4.1) for ELSD method, as mobile phase in a gradient mode. The response with ELSD was fitted to a power function and the DAD response by a linear model over a range of 32-160 μg/mL for CANC and 25-125 μg/mL for HCTZ. The precision and accuracy of the methods were similar, with RSD below 3.0% and recovery between 98.1% and 103.9%. The drugs were subjected to stress conditions of hydrolysis, oxidation, photolysis, humidity and temperature. The degradation products were satisfactory separated from the main peaks and from each other. Both drugs mainly degrade by hydrolysis, showing the formation of one degradation product for HCTZ and two for CANC; its identification was conducted by LC/MS/MS. The methods were successfully applied to the analysis of CANC and HCTZ in combined commercial tablets. The performance of DAD and ELSD methods are comparable, therefore both methods are suitable for stability study and determination of CANC and HCTZ in pharmaceutical samples.