Isotope-Edited Infrared Spectroscopy for Efficient Discrimination between Pharmaceutical Salts and Cocrystals

Tranilast-matrine co-amorphous system: Strong intermolecular interactions, improved solubility, and physiochemical stability

There is a great interest to develop co-amorphous drug delivery systems to enhance the solubility of biopharmaceutics classification system (BCS) class II and IV drugs. However, most reported systems only resulted in severalfold solubility improvement. Tranilast (TRA) is an anti-allergic drug used to treat bronchial asthma and allergic rhinitis. It is a BCS class II drug and its poor aqueous solubility affects its absorption in vivo. To address this issue, a natural alkaloid matrine (MAR) with interesting biological activities was chosen to form a co-amorphous system with TRA, based on the solubility parameter and phase solubility experiment. The TRA-MAR drug-drug co-amorphous system was prepared by the solvent evaporation method, and further characterized by powder X-ray diffraction and modulated temperature differential scanning calorimetry. Fourier transform infrared spectroscopy, FT-Raman, and X-ray photoelectron spectroscopy revealed the formation of salt and the presence of strong intermolecular interactions in the TRA-MAR co-amorphous system, which are also supported by molecular dynamics simulations, showing ionic and hydrogen bonding interactions. This co-amorphous system exhibited excellent physical stability at both 25 °C and 40 °C under anhydrous silica gel condition. Finally, co-amorphous TRA-MAR showed greatly enhanced solubility (greater than 100-fold) and rapid release behavior in the vitro release experiments. NMR spectroscopy revealed the strong intermolecular interactions between TRA and MAR in both DMSO‑d₆ and D₂O. Our study resulted in a TRA-MAR co-amorphous drug system with significant solubility improvement and showcased the great potential to improve the dissolution behaviors of BCS class II and IV drugs through the co-amorphization approach.

Co-amorphous Systems of Sinomenine with Platensimycin or Sulfasalazine: Physical Stability and Excipient-Adjusted Release Behavior

There is strong interest to develop affordable treatments for the infection-associated rheumatoid arthritis (RA). Here, we present a drug-drug co-amorphous strategy against RA and the associated bacterial infection by the preparation and characterization of two co-amorphous systems of sinomenine (SIN) with platensimycin (PTM) or sulfasalazine (SULF), two potent antibiotics. Both of them were comprehensively characterized using powder X-ray diffraction, temperature-modulated differential scanning calorimetry, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The co-amorphous forms of SIN-PTM and SIN-SULF exhibited high T_gs at 139.10 ± 1.0 and 153.3 ± 0.2 °C, respectively. After 6 months of accelerated tests and 1 month of drug-excipient compatibility experiments, two co-amorphous systems displayed satisfactory physical stability. The formation of salt and strong intermolecular interactions between SIN and PTM or SULF, as well as the decreased molecular mobility in co-amorphous systems, may be the intrinsic mechanisms underlying the excellent physical stability of both co-amorphous systems. In dissolution tests, two co-amorphous systems displayed distinct reduced SIN-accumulative releases (below 20% after 6 h of release experiments), which may lead to its poor therapeutic effect. Hence, we demonstrated a controlled release strategy for SIN by the addition of a small percentage of polymers and a small-molecule surfactant to these two co-amorphous samples as convenient drug excipients, which may also be used to improve the unsatisfactory dissolution behaviors of the previously reported SIN co-amorphous systems. Several hydrogen bonding interactions between SIN and PTM or SULF could be identified in NMR experiments in DMSO-d₆, which may be underlying reasons of decreased dissolution behaviors of both co-amorphous forms. These drug-drug co-amorphous systems could be a potential strategy for the treatment of infection-associated RA.

Co-amorphous systems of sinomenine with nonsteroidal anti-inflammatory drugs: A strategy for solubility improvement, sustained release, and drug combination therapy against rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune joint disorder that affects about 1% of the world population and may lead to severe disability and comorbidity. Despite breakthroughs in past decades to understand its pathogenesis and the development of transforming disease-modifying antirheumatic drugs, the symptoms of many patients are not substantially improved. Sinomenine (SIN), a natural alkaloid with poor solubility, has been used to treat RA in China for years because of its unique immunoregulative activity. However, its commercial hydrochloride form has a short half-time, which may cause huge fluctuations of blood drug concentration leading to severe adverse reactions. In this study, co-amorphous systems of SIN with three nonsteroidal anti-inflammatory drugs (NSAIDs), including indomethacin, naproxen, and sulindac, were prepared for the combination therapy, as well as the improvement of its aqueous solubility and controlled release. Each co-amorphous sample was characterized by powder X-ray diffraction (PXRD), temperature-modulated differential scanning calorimetry (mDSC), and Fourier transform infrared spectroscopy (FTIR). The CO₂^- and N⁺H stretching vibration in the three co-amorphous samples appears in FTIR spectra, suggesting the formation of salts between SIN and NSAIDs. SIN also exhibits sustained release rates in all three co-amorphous samples. These co-amorphous systems show excellent physicochemical stability because no recrystallization was observed at 25 °C and 75% relative humidity (RH) after four months. Our study suggests that SIN-NSAIDs co-amorphous systems represent an affordable and promising treatment against RA.

Sinomenine-phenolic acid coamorphous drug systems: Solubilization, sustained release, and improved physical stability

Sinomenine (SIN), isolated from Caulis sinomenii, is a benzyltetrahydroisoquinoline-type alkaloid with potent anti-inflammatory and analgesic effects. SIN-HCl has been used in the forms of tablets or enteric-coated tablets in the treatment of rheumatoid arthritis in China for years, while its short half-life leads to attenuated therapeutic effects and serious side effects. In the current study, three phenolic acids, including salicylic acid (SAA), 2,3-dihydroxybenzoic acid (23DHB), and 2,4-dihydroxybenzoic acid (24DHB), were firstly employed as coamorphous coformers to prepare three binary SIN-phenolic acid coamorphous systems. These new coamorphous systems were characterized by powder X-ray diffraction (PXRD), modulated temperature differential scanning calorimetry (mDSC), and Fourier transform infrared spectroscopy (FTIR). The formation of SIN-phenolic acid coamorphous systems are supported by the absence of diffraction peaks in their PXRD spectra, as well as the single T_gs of three samples (i.e., SIN-SAA, SIN-23DHB, and SIN-24DHB) at 109.5 °C, 124.9 °C, and 135.3 °C. Importantly, the salt formation between SIN and phenolic acids was observed in FTIR. In three coamorphous systems, coamorphous SIN-24DHB shows superior physicochemical stability under both low humidity and accelerated storage conditions. They were also more soluble than crystalline SIN, while were released slower than the commercial SIN-HCl in dissolution experiments. Therefore, our study suggests that phenolic acids may be used as a new type of coformers in the preparation of coamorphous systems for active pharmaceutical ingredients.

Comparison of the crystal structures and physicochemical properties of novel resveratrol cocrystals

Resveratrol (RSV) is one of the most extensively investigated natural polyphenol with potential cardioprotective effects and various biological activities. However, the polymorphism and solvates of RSV cocrystals have not been studied comprehensively. In addition, the relationship between the crystal packing modes and their physicochemical properties of RSV cocrystals remains poorly understood. In this paper, seven novel RSV cocrystals were prepared and characterized by powder X-ray diffraction, single-crystal X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, dynamic vapor sorption, Raman and Fourier transform infrared spectroscopy. Five RSV–4,4′-vinylenedipyridine (DPE) cocrystals were synthesized with polymorphs and solvates, such as RSV–DPE (1:2) in form (I) [RSV–2DPE form (I)], RSV–DPE (1:2) in form (II) [RSV–2DPE form (II)], RSV–DPE (1:1) (RSV–DPE), RSV–DPE (2:3)·acetone (RSV–1.5DPE·0.5ACE), RSV–DPE (1:1.5)·MeOH (RSV–1.5DPE·MeOH). However, RSV–4,4′-ethylenedipyridine (BPE) and RSV–4,4′-azobispyridine (AZPY) cocrystals were prepared as their single crystal forms, that is, RSV–BPE (1:1.5) (RSV–1.5BPE) and RSV–AZPY (1:2) (RSV–2AZPY). RSV–2DPE form (II) can be transformed from RSV–2DPE form (I) during the heating process from single crystal to single crystal. The physicochemical properties of RSV cocrystals are closely related to their crystal packing modes. Also, the conformation and molecular packing of RSV among different cocrystals is flexible. The solubility of RSV–1.5BPE and RSV–2DPE form (II) exhibit higher than RSV in the buffer solution of pH 4.6 and 2.0, respectively. This study may provide a valuable insight into the crystal packing modes of cocrystals which may affect their physicochemical properties.

Confocal Raman micro-spectral evidence and physicochemical evaluation of triamterene salts

Discrimination of active pharmaceutical ingredients (APIs) existing as neutral molecules or salts is essential and complicated. However, the discrimination of pharmaceutical salts by confocal Raman micro-spectroscopy remains relatively poorly understood. In this paper, four new salts of triamterene (Tri) cocrystallized with nicotinic acid (NA), benzoic acid (BA), p-toluenesulfonic acid (TA), or isonicotinic acid (INA) were prepared and characterized comprehensively by powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarized light microscopy (PLM), and dynamic vapor sorption (DVS). Ionized pteridine is identified by marker peaks in the confocal Raman micro-spectra that are characteristic of C[double bond, length as m-dash]N. The single crystal structures of Tri-NA·H2O and Tri-TA further demonstrate that a proton transfers from the carboxylic group of NA or TA to the pyrimidine N1 atom of Tri and their salts formation take place. The intrinsic dissolution rate (IDR) and apparent equilibrium solubility of these four salts are improved compared to the pure Tri component, especially for Tri-BA. This study provides a valuable insight into pharmaceutical salt discrimination by vibrational spectroscopy and presents that the combination of Tri with an acid can be a possible and promising alternative formulation of Tri.

Discrimination and quantification of sulfathiazole polytypes using low-frequency Raman spectroscopy

Low-frequency Raman spectroscopy has advantage to discriminate and quantify polymorphs where common 2D superstructures are piled up with different mode.