Role of Lattice Disorder in Water-Mediated Dissociation of Pharmaceutical Cocrystal Systems

The impact of diluents on the compaction, dissolution, and physical stability of amorphous solid dispersion tablets

Amorphous solid dispersion (ASD) is an effective approach for enhancing the solubility, dissolution, and bioavailability of poorly water-soluble drugs. However, these metastable forms can transform into more thermodynamically stable but less soluble crystalline forms. Despite this challenge, research on processing ASDs into solid dosage forms, such as tablets, is lacking. This work aims to fill this gap by investigating the impact of common diluents on the tableting behavior, dissolution, and physical stability of ASDs composed of itraconazole and hypromellose acetate succinate. Four widely used diluents found in commercially available ASD tablets were selected for the study: microcrystalline cellulose (MCC), anhydrous lactose, starch, and mannitol. The performance of ASD tablets varied significantly depending on the diluent used. Tablets prepared with MCC exhibited higher mechanical strength than those formulated using other diluents. ASD tablets containing mannitol and lactose revealed a faster release rate than those composed of MCC or starch. Notably, the study highlighted that the physical stability of ASDs within a tablet is not solely dependent on the amount of sorbed water; crystalline diluents like lactose and mannitol were found to facilitate ASD recrystallization within a tablet. In summary, the study underscores the importance of excipient selection, considering factors such as mechanical strength, dissolution rate, and physical stability of ASD tablets. These findings offer valuable insights into the selection of excipients for downstream ASD tablet development, leading to improved manufacturability, physical stability, and the overall quality of ASD drug products.

Professor Raj Suryanarayanan: Scientist, Educator, Mentor, Family Man and Giant in Pharmaceutical Research

This special edition of the Journal of Pharmaceutical Sciences is dedicated to Professor Raj Suryanarayanan (Professor and William & Mildred Peters Endowed Chair, University of Minnesota, School of Pharmacy) and honors his extensive and distinguished career as a scientist, educator and mentor. The goal of this commentary is to provide an overview of Professor Suryanarayanan's noteworthy career path and summarize his key research contributions. The commentary concludes with the personal summaries by guest editors.

Azilsartan-nicotinamide cocrystal: Preparation, characterization and in vitro / vivo evaluation

Azilsartan (AZL) is an angiotensin II receptor antagonist, which is mainly used for the treatment of hypertension. AZL has the advantages of high selectivity, hypotensive effect, protection of cardiovascular and cerebrovascular diseases. In order to improve the water solubility of AZL and its bioavailability, AZL -nicotinamide (NA) cocrystal was prepared by mechanical ball milling, and the effect of ball milling conditions on cocrystal preparation were studied. AZL-NA cocrystal was identified and characterized by powder X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy and Fourier transform infrared spectrometry. The results showed that AZL-NA cocrystal with the molar ratio of 1:2 was successfully prepared. And the optimum ball milling condition was milling speed of 300 rpm, milling time of 50 min, the solvent was ethanol/acetonitrile (1:1, v/v), and the solvent dosage (η) was 0.8 μL/mg. The results of solubility tests showed that the solubility of AZL in the cocrystal was 3.39 times higher than the pure drug at 24 h. And the results of vitro dissolution tests showed that the cumulative dissolution of AZL in 2 h was about 10%. While distilled water, pH 1.2 and pH 4.5 acid or buffered solutions and pH 6.8 buffer phosphate salt solution was used as the dissolution medium, the cumulative dissolution of AZL in cocrystal reached 50%, 35%, 55% and 90%, respectively, showing obvious improvement of dissolution. In addition, the accelerated stability tests showed that the AZL-NA cocrystal had good chemical stability. And the pharmacokinetic results showed that AZL-NA cocrystal could significantly improve the bioavailability of AZL.

Investigating the Role of the Reduced Solubility of the Pirfenidone-Fumaric Acid Cocrystal in Sustaining the Release Rate from Its Tablet Dosage Form by Conducting Comparative Bioavailability Study in Healthy Human Volunteers

Pirfenidone (PFD) is the first pharmacological agent approved by the US Food and Drug Administration (FDA) in 2014 for the treatment of idiopathic pulmonary fibrosis (IPF). The recommended daily dosage of PFD in patients with IPF is very high (2403 mg/day) and must be mitigated through additives. In the present work, sustained-release (SR) formulations of the PFD-FA cocrystal of two different strengths such as 200 and 600 mg were prepared and its comparative bioavailability in healthy human volunteers was studied against the reference formulation PIRFENEX (200 mg). A single-dose pharmacokinetic study (200 mg IR vs 200 mg SR) demonstrated that the test formulation exhibited lower C_max and T_max in comparison to the reference formulation, which showed that the cocrystal behaved like an SR formulation. Further in the multiple-dose comparative bioavailability study (200 mg IR thrice daily vs 600 mg SR once daily), the test formulation was found bioequivalent to the reference formulation. In conclusion, the present study suggests that cocrystallization offers a promising strategy to reduce the solubility of PFD and opens the door for potential new dosage forms of this important pharmaceutical.

Crystal surface defects as possible origins of cocrystal dissociation

Atomic force microscopy is used as a characterisation tool to investigate cocrystal dissociation under high relative humidity. Caffeine–glutaric acid as a model system showed possible role of crystal surface defects in the process of cocrystal dissociation.

Use of Atomic Force Microscopy (AFM) to monitor surface crystallization in caffeine-oxalic acid (CAFOXA) cocrystal compacts

Our objective was to monitor the surface crystallization in disordered caffeine-oxalic acid (CAFOXA) cocrystals following exposure to elevated water vapor pressure. This was accomplished using atomic force microscopy (AFM). Disorder was induced in the cocrystal particles by the common pharmaceutical unit operations of milling and compaction. The 'activated' solid, upon exposure to elevated water vapor pressure, had a high propensity to sorb water. This led to a rise in molecular mobility and the surface underwent rapid crystallization to form needle shaped crystals of CAFOXA. Using AFM height and phase imaging, we were able to directly visualize phase transformations on the compact surface. The milled compacts exhibited higher processing induced disorder than the unmilled compacts, thereby accelerating the surface recrystallization.

Recent Advances in Pharmaceutical Cocrystals: From Bench to Market

The pharmacokinetics profile of active pharmaceutical ingredients (APIs) in the solid pharmaceutical dosage forms is largely dependent on the solid-state characteristics of the chemicals to understand the physicochemical properties by particle size, size distribution, surface area, solubility, stability, porosity, thermal properties, etc. The formation of salts, solvates, and polymorphs are the conventional strategies for altering the solid characteristics of pharmaceutical compounds, but they have their own limitations. Cocrystallization approach was established as an alternative method for tuning the solubility, permeability, and processability of APIs by introducing another compatible molecule/s into the crystal structure without affecting its therapeutic efficacy to successfully develop the formulation with the desired pharmacokinetic profile. In the present review, we have grossly focused on cocrystallization, particularly at different stages of development, from design to production. Furthermore, we have also discussed regulatory guidelines for pharmaceutical industries and challenges associated with the design, development and production of pharmaceutical cocrystals with commercially available cocrystal-based products.

Monitoring of Cocrystal Dissociation during the Wet Granulation Process in the Presence of Disintegrants by Using Low-Frequency Raman Spectroscopy

The aim of this study was to evaluate the effect of three coformers and five disintegrants in the granulation formulation on the dissociation of cocrystal during the granulation process by monitoring wet granulation with probe-type low-frequency Raman (LF-Raman) spectroscopy. As model cocrystals, paracetamol (APAP)-oxalic acid (OXA), APAP-maleic acid (MLA), and APAP-trimethylglycine (TMG) were used. The monitoring of the granulation recipe containing cocrystals during wet granulation was performed over time with high-performance LF-Raman spectrometry and the dissociation rate was calculated from the results of multivariate analysis of LF-Raman spectra. The dissociation rate decreased in the order of APAP-TMG, APAP-OXA, and APAP-MLA, showing the same order as observed in Powder X-ray diffraction measurements. Furthermore, to compare the effect of disintegrants on the dissociation rate of APAP-OXA, LF-Raman monitoring was performed for the granulation recipes containing five typical disintegrants (two low-substitution hydroxypropyl cellulose (HPC), cornstarch (CSW), carmellose sodium (CMC), and crospovidone (CRP)). The dissociation rate of APAP-OXA decreased in the order of CSW, HPCs, CMC, and CRP. This difference in the dissociation rate of APAP-OXA was thought to be due to the disintegration mechanism of the disintegrants and the water absorption ratio, which was expected to affect the water behavior on the disintegrant surface during wet granulation. These results suggested that probe-type LF-Raman spectroscopy is useful to monitor the dissociation behavior of cocrystals during wet granulation and can compare the relative stability of cocrystal during wet granulation between different formulations.

Investigating the Influence of Excipients on the Stability of Levothyroxine Sodium Pentahydrate

A range of tablet excipients were evaluated for their influence on the physical form and chemical stability of levothyroxine sodium pentahydrate (LSP; C₁₅H₁₀I₄NNaO₄·5H₂O). LSP-excipient binary powder blends were stored under two conditions: (a) in hermetically sealed containers at 40 °C and (b) at 40 °C/75% RH. By use of synchrotron X-ray diffractometry, the disappearance of LSP could be quantified and the appearance of crystalline levothyroxine (free acid) could be identified. Under hermetically sealed conditions (40 °C) hygroscopic excipients such as povidone induced partial dehydration of LSP to form levothyroxine sodium monohydrate. When stored at 40 °C/75% RH, acidic excipients induced measurable disproportionation of LSP resulting in the formation of levothyroxine (free acid). HPLC analyses of drug-excipient mixtures revealed that lactose monohydrate, microcrystalline cellulose, and croscarmellose sodium caused pronounced chemical decomposition of LSP. On the other hand, magnesium stearate, sodium stearyl fumarate, and alkaline pH modifiers did not affect the physical and chemical stability of the API following storage at 40 °C/75% RH. HPLC, being a solution based technique, revealed chemical decomposition of the API, but the technique was insensitive to physical transformations. Excipient properties such as hygroscopicity and microenvironmental acidity were identified to be critical determinants of both physical and chemical stability of LSP in a drug product. For drugs exhibiting both physical and chemical transformations, simultaneous solid-state and solution based analyses will enable comprehensive stability evaluation.

Cocrystal engineering of pharmaceutical solids: therapeutic potential and challenges

This highlight presents an overview of pharmaceutical cocrystal production and its potential in reviving problematic properties of drugs in different dosage forms. The challenges and future outlook of its translational development are discussed.

Cocrystals "Divorce and Marriage": When a Binary System Meets an Active Multifunctional Synthon in a Ball Mill

A well-defined and stable "AB" binary system in the presence of "C" a crystalline synthon ground in a ball mill undergoes selective transformation in the solid state according to the equation AB+C→AC+B. When the amount of C is increased two times then the equation AB+2C→AC+BC is valid. The other variants are more complex. The pathway BC+A is allowed and leads to the AC and B products. The pathway AC+B is not preferred, and no transformation is observed. These non-obvious correlations were observed for cocrystal of barbituric acid (BA):thiobarbituric acid (TBA) recently reported by Shemchuk et al. (Chem. Commun. 2016, 52, 11815-11818) in the presence of 1-hydroxy-4,5-dimethyl-imidazole 3-oxide (HIMO). This synthon shows high affinity for the BA_0.5 TBA_0.5 cocrystal as well for its individual components, BA and TBA. Single-quantum, double-quantum (SQ-DQ) 2D ¹ H very fast MAS NMR with a spinning rate of 60 kHz was employed as a basic and most diagnostic tool for the study of cocrystals transformations. Analysis of the experimental data was supported by theoretical calculations, including computation of the stabilization energy, E^stab , defined as the energy difference between the energy of a co-crystal and the sum of the energies of particular components in the respective stoichiometric ratios. Two mechanisms of synthon replacement have been proposed. Pathway 1 assumes a concerted mechanism of substitution. In this approach, synthon attack is synchronized in time with the departure of one of the components of the binary system. Pathway 2 implies a non-concerted process, with an intermediate stage in which three separate components are present. Evidence suggesting a preference for Pathway 2 is shown.

Formation of Indomethacin-Saccharin Cocrystals during Wet Granulation: Role of Polymeric Excipients

Formulation of a cocrystal into a solid pharmaceutical dosage form entails numerous processing steps during which there is risk of dissociation. In an effort to reduce the number of unit operations, we have attempted the in situ formation of an indomethacin-saccharin (INDSAC) cocrystal during high-shear wet granulation (HSWG). HSWG of IND (poorly water-soluble drug) and SAC (coformer), with polymers (granulating agents), was carried out using ethanol as the granulation liquid and yielded INDSAC cocrystal granules. Therefore, cocrystal formation and granulation were simultaneously accomplished. Our objectives were to (i) evaluate the influence of polymers on cocrystal formation kinetics during wet granulation and (ii) mechanistically understand the role of polymers in facilitating the cocrystal formation. Polyvinylpyrrolidone (PVP), hydroxypropyl cellulose (HPC), and polyethylene oxide (PEO) were chosen to investigate the influence of soluble polymers. The cocrystal formation kinetics was influenced by the polymer (PVP < HPC < PEO) and its concentration. The interaction of the polymer with cocrystal components inhibited the cocrystal formation. Complete cocrystal formation was observed in the presence of PEO, a polymer which does not interact with IND and SAC.