Polymorphic Crystallization and Transformation of Candesartan Cilexetil

Solid dispersion systems for enhanced dissolution of poorly water-soluble candesartan cilexetil: In vitro evaluation and simulated pharmacokinetics studies

BACKGROUND

Candesartan cilexetil (CC) is a selective angiotensin II receptor antagonist widely used to treat hypertension. CC is a substrate of P-glycoprotein (P-gp), causing its efflux to the intestinal lumen. It is also practically insoluble in water and has low oral bioavailability (14%). Thus, the current study aims to improve the in vitro dissolution of CC by developing solid dispersion systems (SDSs) and corroborating the in vitro results using a simulated pharmacokinetics study.

METHODS

The SDSs were prepared using polyvinyl pyrrolidone (PVP) as a water-soluble polymer, Eudragit E100 (EE100) as a pH-dependent soluble carrier, and a combination of these two polymers. The saturation solubility and the dissolution rate studies of the prepared systems in three dissolution media were performed. The optimized system SE-EE5 was selected for further investigations, including DSC, XRD, FTIR, FESEM, DLS, TSEM, IVIVC convolution study, and stability studies.

RESULTS

The solubility of CC significantly increased by a factor of 27,037.344 when formulated as a solid dispersion matrix using EE100 at a ratio of 1:5 (w/w) drug to polymer (SE-EE5 SD), compared to the solubility of the pure drug. The mechanism of solubility and dissolution rate enhancement of CC by the optimized SDS was found to be via the conversion of the crystalline CC into the amorphous form as well as nanoparticles formation upon dissolution at a pH below 5. The instrumental analysis tests showed good compatibility between CC and EE100 and there was no chemical interaction between the drug and the polymer. Moreover, the stability tests confirmed that the optimized system was stable after three months of storage at 25°C.

CONCLUSION

The utilization of the solid dispersion technique employing EE 100 polymer as a matrix demonstrates significant success in enhancing the solubility, dissolution, and subsequently, the bioavailability of water-insoluble drugs like CC.

Long-Chain Bio-Based Nylon 514 Salt: Crystal Structure, Phase Transformation, and Polymerization

Nylon 514 is one of the new long-chain bio-based nylon materials; its raw material, 1,5-pentanediamine (PDA), is prepared by biological techniques, using biomass as the raw material. The high-performance monomer of nylon 514, 1,5-pentanediamine-tetradecanedioate (PDA-TDA) salt, was obtained through efficient crystallization methods. Here, two crystal forms of PDA-TDA, anhydrous and dihydrate, were identified and studied in this paper. From the characterization data, their crystal structures and thermal behaviors were investigated. Lattice energy was calculated to gain further insight into the relationship between thermal stability and crystal structures. The contribution of hydrogen bonds and other intermolecular interactions to the crystal structure stability have been quantified according to detailed Hirshfeld and IRI analyses. Additionally, the transformation mechanism of the anhydrate and dihydrate was established through a series of well-designed stability experiments, in which the temperature and water activity play a significant role in the structural stability of crystalline forms. Eventually, we obtained nylon 514 products with good thermal stability and low absorption using stable dihydrate powders as monomers. The properties of nylon 514 products prepared by different polymerization methods were also compared.

The effect of polymorphism on polymer properties: crystal structure, stability and polymerization of the short-chain bio-based nylon 52 monomer 1,5-pentanediamine oxalate

The compound 1,5-pentanediamine (PDA) is prepared by biological methods using biomass as raw material. The salt of 1,5-pentanediamine oxalate (PDA-OXA) was used directly as the monomer for the preparation of a new bio-based nylon 52 material. High-performance polymer materials require initial high-quality monomers, and crystallization is an essential approach to preparing such a monomer. In this work, three crystal forms of PDA-OXA, the anhydrate, dihydrate and trihydrate, were found and the single crystals of two hydrates were obtained. Their crystal structures were determined using single-crystal and powder X-ray diffraction. The thermal behaviors were characterized by thermodynamic analysis, and the lattice energy was calculated to further explore the relationship between the thermal stability and crystal structure. Detailed computational calculations, Hirshfeld analyses and lattice energy calculations were performed to quantify both the contribution of intra- and intermolecular interactions to the supramolecular assembly, as well as the influence on the stability of the structure. The structure-property relationship between the PDA-OXA crystal forms was established. Moreover, the phase transformation mechanism between the crystalline forms of PDA-OXA has been established, and the control strategy of specific crystal forms was developed from the water activity-temperature phase diagram and relevant thermodynamic data. Finally, the influence of the polymorphism of the monomer and the polymerization methods on the properties of the polymer was investigated. The nylon 52 product obtained showed good appearance, high hardness and thermal stability, the polymer made using the anhydrate as the monomer has better thermodynamic properties than that prepared from the dihydrate, indicating practical industrial application prospects.

Ultrasound-assisted theophylline polymorphic transformation: Selective polymorph nucleation, molecular mechanism and kinetics analysis

In this paper, the ultrasound-assisted solvent-mediated polymorphic transformation of theophylline was explored in detail. The induction time and reconstruction time were significantly decreased by ultrasound, thereby decreasing the total transformation time and promoting the transformation process. The ultrasound-promoted efficiency of nucleation was different in three alcoholic solvents, which was difficult to explain by traditional kinetic effects. To resolve the above confusion, binding energies calculated by Density Functional Theory were applied to explore the relationship between the ultrasound-promoted efficiency of nucleation and solute-solvent interactions. Then, a possible molecular self-assembly nucleation pathway affected by ultrasound was proposed: the ultrasound could change and magnify the crucial effect of the specific sites of solute-solvent interactions in the nucleation process. Finally, the transformation kinetics with different effective ultrasonic energies was quantitatively analyzed by Avrami-Erofeev model, indicating that the dissolution element in the rate-limiting step was gradually eliminated by higher ultrasonic energy. Fortunately, the elusive crystal form V could be easily obtained by the ultrasound-assisted polymorph transformation. This proved to be a robust method to produce high purity form V of theophylline. The outcome of this study demonstrated that the proper ultrasonic irradiation had the potential to produce specific polymorphs selectively.

Monohydrate and anhydrate of nylon 5I monomer 1,5-pentanediamine-isophthalate

Nylon 5I is one of the new bio-based nylon materials. Its raw material 1,5-pentanediamine (PDA) is prepared by biological methods using biomass as the raw material. The high-performance polymer materials require the original high-quality monomers. 1,5-Pentanediamine–isophthalate (PDA–IPA) was taken as the direct monomer for the preparation of nylon 5I, and the crystallization was a valuable and essential approach to preparing the good-performance monomer salt. In this report, we found and obtained two crystal forms of PDA–IPA, monohydrate and an anhydrous form. Their crystal structures were determined and analyzed by single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), and Fourier transform infrared spectroscopy (FTIR). Hirshfeld surface maps were employed to capture the differences in the interactions present in the two forms. The thermal behaviors were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Moreover, the monohydrate and anhydrous phase can transform to each other through solid–solid transformation or solution-mediated phase transformation, and the critical values of the phase transformation were determined. Finally, the relative stability of the two forms under different thermodynamic conditions was discussed, especially the influence of temperature and water activity on the stability.

Monohydrate and anhydrous phases of PDA–IPA single crystals have been identified by single crystal X-ray diffraction. The monohydrate and anhydrate phases can achieve mutual transformation under certain conditions, and depend strongly on the temperature and water activity.

Crystal forms and phase transformation of 1,5-pentanediamine-terephthalate: a bio-based nylon 5T monomer

Nylon 5T is one of the bio-based nylons, its raw material 1,5-pentanediamine is derived from biomass resources and produced by biological methods. 1,5-pentanediamine-terephthalate (PDA-TPA) is the monomeric salt for nylon 5T polymerization, and its own product quality has a significant impact on the performance of nylon 5T. PDA-TPA was prepared by anti-solvent crystallization in this study. It exists in two solid forms, a monohydrate [form (I)] and an anhydrous phase [form (II)]. The transition temperature of the two phases was around 65°C in the given ethanol-water binary (7:1) mixture. The characterization of monohydrate and anhydrate phases regarding structures and stabilities was carefully carried out using powder X-ray diffraction, single crystal X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, hot-stage microscopy and Fourier transform infrared spectroscopy. The relationship between the molecular interactions of monohydrate and anhydrate phases under different packing architectures and their thermal behaviours was analysed and established. In addition, the relationships between the structures and thermal behaviours for the two solid forms were analysed and established. In addition, the effect of solvent on phase conversion, the relationships between the temperature and water activity, as well as the relative stability of monohydrate and anhydrate phases under different thermodynamic conditions, were investigated by solid-solid transformation and solvent-mediated transformation experiments. It was obvious that the transition temperature of monohydrate and anhydrate phases of PDA-TPA was significantly influenced by water activity, and the larger the value of water activity is, the higher is the transition temperature. These studies give insight into the transformation of nylon 5T monomer salt and contribute to the control of target crystal preparation.

Kinetic estimation of solid state transition during isothermal and grinding processes among efavirenz polymorphs

Investigation into the solid-state transition among drug polymorphs has been more intense lately. Many factors induce the transformation of polymorphs during manufacturing processes. Efavirenz (EFV), an AIDS therapy drug, has more than 23 polymorphs, but very little information has been reported on them. This study aimed to perform a characterisation of EFV polymorph properties and to predict the kinetics and mechanism of the polymorphic transformation of EFV during manufacturing processes. The bimorphism study was conducted by Differential Scanning Calorimetry (DSC) thermal analysis. The phase transition kinetics of the polymorphs was monitored by X-ray powder diffraction and the quantification of concomitant polymorphs was examined using Rietveld refinement with MAUD ver. 2.7 as a software aid. To predict the solid-state transition, correlation coefficients of solid-state kinetic models were fitted to the experimental data. The results show that Form I and Form II of EFV were thermodynamically shown to be monotropy related. By fitting the experimental data, it was found that isothermal treatment had the best model fit with the phase boundary reaction in the two-dimensional model (G2). Accordingly, by employing mechanical treatment (grinding), it was predicted that the transition mechanism is a second-ordered reaction (R2). The activation energy of the transition during isothermal treatment calculated by the Arrhenius plot was found to be 23.051 kJ mol-1; the half-lif of Form II at ambient temperature was 428.05 min (~7.1 h).

Solid State Stability and Kinetics of Degradation for Candesartan-Pure Compound and Pharmaceutical Formulation

The aim of this work was to assess the impact of an excipient in a pharmaceutical formulation containing candesartan cilexetil over the decomposition of the active pharmaceutical ingredient and to comparatively investigate the kinetics of degradation during thermolysis in an oxidative atmosphere under controlled thermal stress. To achieve this, the samples were chosen as follows: pure candesartan cilexetil and a commercial tablet of 32 mg strength. As a first investigational tool, Universal attenuated total reflection Fourier transform infrared (UATR-FTIR) spectroscopy was chosen in order to confirm the purity and identity of the samples, as well as to check if any interactions took place in the tablet between candesartan cilexetil and excipients under ambient conditions. Later on, samples were investigated by thermal analysis, and the elucidation of the decomposition mechanism was achieved solely after performing an in-depth kinetic study, namely the use of the modified non-parametric kinetics (NPK) method, since other kinetic methods (American Society for Testing and Materials—ASTM E698, Friedman and Flynn–Wall–Ozawa) led to inadvertencies. The NPK method suggested that candesartan cilexetil and the tablet were degraded by the contribution of two steps, the main being represented by chemical degradation and the secondary being a physical transformation. The excipients chosen in the formulation seemed to have a stabilizing effect on the decomposition of the candesartan cilexetil that was incorporated into the tablet, relative to pure active pharmaceutical ingredient (API), since the apparent activation energy for the decomposition of the tablet was 192.5 kJ/mol, in comparison to 154.5 kJ/mol for the pure API.

Preparation, crystal structure and solution-mediated phase transformation of a novel solid-state form of CL-20

The crystal structure, thermodynamic phase diagram, and polymorphic transformation behaviors of CL-20 acetonitrile solvate are systematically investigated.

In Situ Monitoring and Modeling of the Solution-Mediated Polymorphic Transformation of Rifampicin: From Form II to Form I

In this article, the solution-mediated polymorphic transformation of rifampicin was investigated and simulated in 3 solvents at 30°C. The solid-state form I and form II of rifampicin was characterized by powder X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). To explore the relative stability, solubility data of form I and form II of rifampicin in butan-1-ol were determined using a dynamical method. In addition, Raman spectroscopy and focused beam reflectance measurement were used to in situ monitor the transformation of rifampicin from form II to form I. The liquid state concentration of rifampicin was measured by UV spectroscopic method. To investigate the effect of solvent on transformation, the transformation experiments were carried out in 3 solvents. Furthermore, a mathematical model was built to describe the kinetics of dissolution, nucleation, and growth processes during transformation by using experimental data. By combination of experimental and simulation results, it was found that the transformation process of rifampicin is controlled by dissolution of form II in heptane, whereas the transformation in hexane and octane was firstly controlled by dissolution of solid-state form and then controlled by growth of form I.

Understanding pharmaceutical polymorphic transformations II: crystallization variables and influence on dosage forms

Excipients or formulation variables have often been exploited to improve stability, modify release, or improve physicochemical properties of dosage forms. In pharmaceutical field, it is generally expected that excipients work at macromolecular level where they might influence the crystal structure of a solid. These polymers/colloidal particles may modify the rate and direction of crystal growth. It has also been observed, that different polymorphic crystals exhibit different colors on exposure to same colorant, predominantly due to difference in surface pH of different crystal lattices. Apart from physicochemical affect, crystal habit also influences pharmacokinetic parameters of the dosage form. Crystals with smaller size or lower lattice energy have shown to exhibit higher bioavailability with faster rate of release.

Understanding pharmaceutical polymorphic transformations I: influence of process variables and storage conditions

The active pharmaceutical ingredient (API) of a dosage form is affected by number of mechanical and environmental factors which have a tendency to alter its crystalline state. Polymorphic transitions have been observed to occur during various unit operations like granulation, milling and compression. Forces of pressure, shear and temperature have an ability to induce alterations in crystal habit. A conversion in polymorphic form during a unit operation is very likely to affect the handling of API in the subsequent unit operation. Transitions have also been observed during storage of formulations where the relative humidity and temperature play a major role. An increase in temperature during storage can dehydrate or desolvate the crystal and hence produce crystal defects, whilst, high humidity conditions produce higher molecular mobility leading to either crystallization of API or alteration of its crystalline form.

The in situ monitoring of the transformation of moxidectin ethanol solvate to form I in an ethanol–water mixture

Moxidectin is a single-component and semisynthetic macrocyclic lactone antibiotic, which has been widely used in the prevention and treatment of parasites in farm animals.