Thermal behavior and phase identification of Valsartan by standard and temperature-modulated differential scanning calorimetry

Valsartan/2-Aminopyridine Co-Amorphous System: Preparation, Characterization, and Supramolecular Structure Simulation by Density Functional Theory Calculation

The objective of this work was to improve the solubility and discover a stable co-amorphous form of valsartan (VAL), a BCS class-II drug, by utilizing small molecule 2-Aminopyridine (2-AP) in varying molar ratios (2:1, 1:1, and 1:2), employing a solvent evaporation technique. Additionally, by way of a density functional theory (DFT)-based computational method with commercially available software, a new approach for determining the intermolecular connectivity of multi-molecular hydrogen bonding systems was proposed. The binary systems' features were characterized by PXRD, DSC, FTIR, and Raman spectroscopy, while the equilibrium solubility and dissolution was determined in 0.1 N HCL and water conditions to investigate the dissolution advantage of the prepared co-amorphous systems. The results demonstrated that the co-amorphous system was successfully prepared in VAL/2-AP with a 1:2 molar ratio following solvent evaporation, whereby the hydrogen bonding sites of VAL were fully occupied. Physical stability studies were carried out under dry conditions at room temperature for 6 months. Furthermore, four possible ternary systems were constructed, and their vibrational modes were simulated by DFT calculations. The calculated infrared spectra of the four configurations varied widely, with trimer 1 showing the most resemblance to the experimental spectrum of the co-amorphous 1:2 system. Additionally, co-amorphous VAL/2-AP displayed significant improvement in the solubility and dissolution study. Notably, in the 1:2 ratio, there was almost a 4.5-fold and 15.6-fold increase in VAL's solubility in 0.1 N HCL and water environments, respectively. In conclusion, our findings highlight the potential of co-amorphous systems as a feasible approach to improving the properties and bioavailabilities of insoluble drugs. The proposed simulation method provides valuable insights into determining the supramolecular structure of multi-molecular hydrogen bonding systems, offering a novel perspective for investigating such systems.

Different or the same? exploring the physicochemical properties and molecular mobility of celecoxib amorphous forms

The influence of different preparation methods on the physicochemical properties of amorphous solid forms have gained considerable attention, especially with recent publications on pharmaceutical polyamorphism. In the present study, we have investigated the possible occurrence of polyamorphism in the drug celecoxib (CEL) by investigating the thermal behavior, morphology, structure, molecular mobility and physical stability of amorphous CEL obtained by quench-cooling (QC), ball milling (BM) and spray drying (SD). Similar glass transition temperatures but different recrystallization behaviors were observed for CEL-QC, CEL-BM and CEL-SD using modulated differential scanning calorimetry analysis. A correlation between the different recrystallization behaviors of the three CEL amorphous forms and the respective distinct powder morphologies, was also found. Molecular dynamics simulations however, reveal that CEL presents similar molecular conformational distributions when subjected to QC and SD. Moreover, the obtained molecular conformational distributions of CEL are different from the ones found in its crystal structure and also from the ones found in the lowest-energy structure obtained by quantum mechanical calculations. The type and strength of CEL hydrogen bond interactions found in CEL-QC and CEL-SD systems are almost identical, though different from the ones presented in the crystal structure. Pair distribution function analyses and isothermal microcalorimetry show similar local structures and structural relaxation times, respectively, for CEL-QC, CEL-BM and CEL-SD. The present work shows that not only similar physicochemical properties (glass transition temperature, and structural relaxation time), but also similar molecular conformational distributions were observed for all prepared CEL amorphous systems. Hence, despite their different recrystallization behaviors, the three amorphous forms of CEL did not show any signs of polyamorphism.

Coamorphous Systems of Valsartan: Thermal Analysis Contribution to Evaluate Intermolecular Interactions Effects on the Structural Relaxation

Coamorphous formation in binary systems of valsartan (Val) with 4,4'-bipyridine (Bipy) and trimethoprim (Tri) was investigated for mixtures with a mole fraction of 0.16~0.86 of valsartan and evaluated in terms of the glass transition temperature. The glass transition of the systems had a behavior outside the values predicted by the Gordon-Taylor equation, showing that Val-Bipy (hydrogen bonding between the components) had a lower deviation and Val-Tri (ionic bonding between the components) had a higher deviation. Mixtures of compositions 2:1 Val-Bipy and 1:1 Val-Tri were selected for further investigation and verified to be stable, as no crystallization was observed during subsequent heating and cooling programs. For these systems, the effective activation energy during glass transition was evaluated. Compared to pure valsartan, the system with the lower glass transition temperature (Val-Bipy) presented the highest effective activation energy, and the system with the higher glass transition temperature (Val-Tri) presented a lower effective activation energy. The results presented a good correlation between the data obtained from two different techniques to determine the fragility and effective activation energy: non-isothermal kinetic analysis by DSC and TSDC.

Improvement of dissolution profile of eplerenone with solidified self-emulsifying drug delivery systems (S-SEDDS)

BACKGROUND

Eplerenone is a member of antihypertensives used individually or in combination with other medicines. Eplerenone exhibits poor solubility and is considered a class II drug.

OBJECTIVE

Increasing the solubility of eplerenone by using both liquid and solid self-emulsifying drug delivery system as an alternative to its marketed tablet product.

METHODS

Solubility studies of eplerenone were done with different oils, surfactants, and co-surfactants to determine which one has the highest solubility for eplerenone and determine the preference in the formulations of liquid self-emulsifying drug delivery system. The solidification process was carried out with the adsorption to solid carrier method. Optimal ratios of components were specified with pseudo-ternary phase diagram technique. Self-emulsifying drug delivery system formulations were characterized in terms of chemical interaction, droplet size/distribution, crystallization behaviors, and rheological evaluation. In vitro drug release studies were conducted and compared to pure drug and marketed product.

RESULTS

The solubility screening results showed high solubility of EPL in triacetin (11.99 mg/mL) as oil, Kolliphor®EL (≈ 2.65 mg/mL), and Tween^®80 (≈ 1.91 mg/mL) as surfactant and polyethylene glycol 200 (PEG200) (≈ 8.50 mg/mL), dimethyl sulfoxide (≈ 7.57 mg/mL), Transcutol^®P (≈ 6.03 mg/mL) as co-surfactant, respectively. Rheology studies revealed that liquid self-emulsifying drug delivery formulations exhibited non-Newtonian pseudoplastic flow.

CONCLUSION

Solid self-emulsifying drug delivery systems prepared with Aerosil and Neusilin have shown tremendous improvement in terms of eplerenone dissolution by releasing the entire dose with boosted effect within 5 and 30 minutes respectively compared to the marketed product and pure eplerenone (p < 0.05).

Low-Frequency Raman Spectroscopy as an Avenue to Determine the Transition Temperature of β- and γ-Relaxation in Pharmaceutical Glasses

In an earlier investigation, low-frequency Raman (LFR) spectroscopy was shown to detect the transition temperature of the β-relaxation (T_β) in both amorphous celecoxib and various celecoxib amorphous solid dispersions [Be̅rziņš, K. Mol. Pharmaceutics 2021, 18(10), 3882-3893]. In this study, we further investigated the application of this technique to determine T_β, an important parameter for estimating crystallization potency of amorphous drugs. Alongside commercially available amorphous drugs (zafirlukast and valsartan disodium salt), differently melt-quenched samples of cimetidine were also analyzed. Overall, the variable-temperature LFR measurements allowed for an easy access to the desired information, including the even lesser transition of the tertiary relaxation motions (T_γ). Thus, the obtained results not only highlighted the sensitivity, but also the practical usefulness of this technique to elucidate (subtle) changes in molecular dynamics within amorphous pharmaceutical systems.

Design and physico-mechanical evaluation of fast-dissolving valsartan polymeric drug delivery system by electrospinning method

Objective(s):

Chronic hypertension is a pervasive morbidity and the leading risk factor for cardiovascular diseases. Valsartan, as an antihypertensive drug, has low solubility and bioavailability. The application of orodispersible films of valsartan is suggested to improve its bioavailability. With this dosage form, the drug dissolves rapidly in saliva and is absorbed readily without the need for water.

Materials and Methods:

For this purpose, valsartan with polyvinylpyrrolidone (PVPK90) polymer were exposed to the electrospinning technique to construct orodispersible nanofilms. The optimum obtained nanofiber, selected by Design-Expert software, was evaluated in terms of mechanical strength for evaluation of the flexibility and fragility of the nanofibers. The drug content, wettability, and disintegration tests, as well as the release assessment of the nanofibers, were performed followed by DSC, FTIR, and XRD assays.

Results:

The uniform nanofibers’ diameter increased with the increase of the polymer concentration. The tensile test verified a stress reduction at the yield point as the polymer concentration increased. Then, the 492 nm nanofiber with above 90% drug encapsulation, containing 8% polymer and 18% valsartan made below 9 kV, was selected. The wetting time was less than 30 sec and over 90% of the drug was released in less than 2 min. The XRD and DSC studies also confirmed higher valsartan solubility due to the construction alternations in nanofibers. The FTIR examination indicated the chemical bonding between the drug and the polymer.

Conclusion:

The selected nanofibers of valsartan present the essential drug feature and acceptable drug release for further investigations.

Nanostructured Valsartan Microparticles with Enhanced Bioavailability Produced by High-Throughput Electrohydrodynamic Room-Temperature Atomization

The high-throughput drying and encapsulation technique called electrospraying assisted by pressurized gas (EAPG) was used for the first time to produce nanostructured valsartan within microparticles of excipients. Valsartan, a poorly absorbed and lipid-soluble drug, was selected since it is considered a good model for BCS class II drugs. Two different polymeric matrices were selected as excipients, i.e., hydroxypropyl methylcellulose (HPMC) and lactose monohydrate, while Span 20 was used as a surfactant. The produced 80% valsartan loading formulations were characterized in terms of morphology, crystallinity, in vitro release, in vitro Caco-2 cells’ permeability, and in vivo pharmacokinetic study. Spherical microparticles of ca. 4 μm were obtained within which valsartan nanoparticles were seen to range from 150 to 650 nm. Wide-angle X-ray scattering and differential scanning calorimetry confirmed that valsartan had a lower and/or more ill-defined crystallinity than the commercial source, and photon correlation spectroscopy and transmission electron microscopy proved that it was dispersed and distributed in the form of nanoparticles of controlled size. In vitro dissolution tests showed that the HPMC formulation with the lowest API particle size, i.e., 150 nm, dissolved 2.5-fold faster than the commercial valsartan in the first 10 min. This formulation also showed a 4-fold faster in vitro permeability than the commercial valsartan and a 3-fold higher systemic exposure than the commercial sample. The results proved the potential of the EAPG processing technique for the production of safe-to-handle microparticles containing high quantities of a highly dispersed and distributed nanonized BCS class II model drug with enhanced bioavailability.

Dual-drug amorphous formulation of gliclazide

Amorphization is a well-established strategy to enhance the dissolution properties of poorly water-soluble drugs. However, the amorphous state is inherently unstable toward recrystallization. Coamorphous systems of a drug and a small-molecule excipient or of two complementary drugs often show an enhanced stability. Diabetes and hypertension are frequently coexistent. In this paper a study on the coamorphization of the poorly water-soluble antidiabetic drug gliclazide (glz) and the antihypertensive drug valsartan (val) is reported. Amorphous glz recrystallized after 1 d under ambient conditions, whereas coamorphous glz-val containing glz and val in a 1:1 or 1:2 molar ratio was stable for at least four months at 20 °C and 56% relative humidity. The dissolution rate of glz increased in the order crystalline glz < glz-val_1:1 < glz-val_1:2. Furthermore, ternary coamorphous systems of glz, val and an excipient were prepared; glz-val_1:1_PVP, glz-val_1:1_HPC, glz-val_1:1_ALM, glz-val_1:1_MCC (PVP = polyvinylpyrrolidone, HPC = hydroxypropyl cellulose, ALM = α-lactose monohydrate, MCC = microcrystalline cellulose). MCC and HPC did not affect the stability of the coamorphous system, while ALM promoted the recrystallization of glz in glz-val_1:1_ALM during storage and freshly prepared glz-val_1:1_PVP contained small amounts of crystalline glz. Glz-val_1:1_MCC showed enhanced dissolution properties compared to crystalline glz and glz-val_1:1 and is a viable fixed-dose formulation.

Sacubitril-valsartan cocrystal revisited: role of polymer excipients in the formulation

Objectives: This study investigated the impact of polymer excipients on a typical cocrystal for sacubitril (SAC) and valsartan (VAL), aiming to guide optional formulation design and maximize oral bioavailability.Methods: Poly vinyl pyrrolidone (PVP) and hydroxypropyl cellulose (HPC) and hydroxypropyl methylcellulose (HPMC) were selected. The dissolution/permeation system was used to predict both the kinetics of drug supersaturation and the simple permeation. The intermolecular interaction was analyzed by ¹H NMR spectroscopy and molecular dynamics simulation. Pharmacokinetic study was performed to assess the impact of polymer excipients in vivo.Results: Our study found that unappreciated excipients in the formulation, especially some polymers, might compete with the intermolecular hydrogen bonding among the cocrystals components and provide unexpected affinity, and thus leverage the therapeutic benefits. HPMC as a coating excipient used in the Entresto® tablet hampered the supersaturation of API, which led to the poor oral absorption of cocrystals. Conversely, PVP appeared to promote and maintain drug supersaturation, resulting in improved bioavailability of API.Conclusion: In conclusion, understanding the interplay between the cocrystal components and polymers is the key to optimizing the excipients to maximize the performance of cocrystal based oral drug formulation.

Combining Co-Amorphous-Based Spray Drying with Inert Carriers to Achieve Improved Bioavailability and Excellent Downstream Manufacturability

It is crucial to improve poorly water-soluble orally administered drugs through both preclinical and therapeutic drug discovery. A co-amorphous formulation consisting of two low molecular weight (MW) molecules offers a solubility/dissolubility advantage over its crystalline form by maintaining their amorphous status. Here, we report on a co-amorphous solid dispersion (SD) system that includes inert carriers (lactose monohydrate or microcrystalline cellulose) and co-amorphous sacubitril (SAC)-valsartan (VAL) using the spray drying process. The strong molecular interactions between drugs were the driving force for forming robust co-amorphous SDs. Our system provided the highest solubility with more than ~11.5- and 3.12-times solubility increases when compared with the physical mixtures. Co-amorphous lactose monohydrate (LM) SDs showed better bioavailability of APIs (~356.27.8% and 154.01% for the relative bioavailability of LBQ 657 and valsartan, respectively). Co-amorphous inert carrier SDs possessed an excellent compressibility for the production of a direct compression pharmaceutical product. In conclusion, these brand-new co-amorphous SDs could reduce the number of unit processes to produce a final pharmaceutical product for downstream manufacturability.

Thermal behavior and molecular mobility in the glassy state of three anti-hypertensive pharmaceutical ingredients

Good agreement was found between the thermodynamic and kinetic fragilities of these APIs. DSC analysis of irbesartan showed the possibility of transformation A → B between the two monotropic polymorphic forms.

Characterization of Two Distinct Amorphous Forms of Valsartan by Solid-State NMR

Valsartan (VAL) is an antihypertensive drug marketed in an amorphous form. Amorphous materials can have different physicochemical properties depending on preparation method, thermal history, etc., but the nature of such materials is difficult to study by diffraction techniques. This study characterizes two different amorphous forms of valsartan (AR and AM) using solid-state NMR (SSNMR) as a primary investigation tool, supported by solution-state NMR, FT-IR, TMDSC, and dissolution tests. The two forms are found to be clearly distinct, with a significantly higher level of structural arrangement in the AR form, as observed in (13)C, (15)N, and (1)H SSNMR. (13)C and (15)N NMR indicates that the fully amorphous material (AM) contains an approximately equal ratio of cis-trans conformers about the amide bond, whereas the AR form exists mainly as one conformer, with minor conformational "defects". (1)H ultrafast MAS NMR shows significant differences in the hydrogen bonding involving the tetrazole and acid hydrogens between the two materials, while (15)N NMR shows that both forms exist as a 1,2,3,4-tetrazole tautomer. NMR relaxation times show subtle differences in local and bulk molecular mobility, which can be connected with the glass transition, the stability of the glassy material, and its response to aging. Counterintuitively the fully amorphous material is found to have a significantly lower dissolution rate than the apparently more ordered AR material.

Valsartan

Valsartan is an antihypertensive drug which selectively inhibits angiotensin receptor type II. Generally, valsartan is available as film-coated tablets. This review summarizes thermal analysis, spectroscopy characteristics (UV, IR, MS, and NMR), polymorphism forms, impurities, and related compounds of valsartan. The methods of analysis of valsartan in pharmaceutical dosage forms and in biological fluids using spectrophotometer, CE, TLC, and HPLC methods are discussed in details. Both official and nonofficial methods are described. It is recommended to use LC-MS method for analyzing valsartan in complex matrices such as biological fluids and herbal preparations; in this case, MRM is preferred than SIM method.

Bisoprolol and bisoprolol-valsartan compatibility studied by differential scanning calorimetry, nuclear magnetic resonance and X-ray powder diffractometry

Purpose

The objective of this study was to evaluate the thermal behavior of crystalline and amorphous bisoprolol fumarate and its compatibility with amorphous valsartan. This pharmacologically relevant drug combination is a potential candidate for fixed-dose combination formulation.

Methods

DSC and TMDSC were used to examine thermal behavior of bisoprolol fumarate. SSNMR and XRPD were applied to probe the solid state forms. The thermal behavior of physical mixtures with different concentrations of bisoprolol and valsartan were examined by DSC and TMDSC, and the observed interactions were investigated by XRPD, solution- and solid-state NMR.

Results

The phase transitions from thermal methods and solid-state NMR spectra of crystalline and amorphous bisoprolol fumarate are reported. Strong interactions between bisoprolol fumarate and valsartan were observed above 60 C, resulting in the formation of a new amorphous material. Solution- and solid-state NMR provided insight into the molecular nature of the incompatibility.

Conclusions

A combined analysis of thermal methods, solution- and solid-state NMR and XRPD experiments allowed the investigation of the conformational and dynamic properties of bisoprolol fumarate. Since bisoprolol fumarate and valsartan react to form a new amorphous product, formulation of a fixed-dose combination would require separate reservoirs for bisoprolol and valsartan to prevent interactions. Similar problems might be expected with other excipients or APIs containing carboxylic groups.

Electronic supplementary material

The online version of this article (doi:10.1007/s11095-014-1471-7) contains supplementary material, which is available to authorized users.

Uniform nano-sized valsartan for dissolution and bioavailability enhancement: influence of particle size and crystalline state

The central purpose of this study was to evaluate the impact of drug particle size and crystalline state on valsartan (VAL) formulations in order to improve its dissolution and bioavailability. VAL microsuspension (mean size 22 μm) and nanosuspension (30-80nm) were prepared by high speed dispersing and anti-solvent precipitation method and converted into powders through spray drying. Differential scanning calorimetry studies indicated amorphization of VAL in the spray-dried valsartan nanosuspension (SD-VAL-Nano) but recrystallization occurred after 6 months storage at room temperature. The spray-dried valsartan microsuspension (SD-VAL-Micro) conserved the crystalline form. The VAL dissolution rate and extent were markedly enhanced with both SD-VAL-Micro and SD-VAL-Nano as compared to crude VAL crystals over the pH range of 1.2-6.8. Pharmacokinetic studies in rats demonstrated a 2.5-fold increase in oral bioavailability in the case of SD-VAL-Nano compared with the commercial product while the SD-VAL-Micro provided a much less desirable pharmacokinetic profile. In conclusion, reducing particle size to the nano-scale appears to be a worthwhile and promising approach to obtain VAL products with optimum bioavailability. In addition, the impact of crystalline state on the bioavailability of nano-sized VAL might be not as big as that of particle size.