Preparation and Dehydration Kinetics of Complex Sulfadiazine Calcium Hydrate with Both Channel-Type and Coordinated Water

A potential cocrystal strategy to tailor in-vitro dissolution and improve Caco-2 permeability and oral bioavailability of berberine

Berberine hydrochloride (BER), a promising candidate in treating tumors, diabetes and pain management, has relatively low oral absorption and bioavailability due to its low intestinal permeability. To address these challenges, we developed a BER and lornoxicam cocrystal (BLCC) by a solvent evaporation method and characterized it using X-ray diffraction, differential scanning calorimetry and thermogravimetric analysis. Compared with BER, BLCC exhibited an instant release in pH 1.0 HCl and a sustained release up to 24 h in pH 6.8 buffer solutions and water. The Caco-2 permeability of BLCC has shown a remarkable increase compared to that of BER (i.e., Papp(a→b): 50.30 × 10-7vs 8.82 × 10-7 cm/s), which is attributed to the improved lipophilicity of BER (i.e., log P: 1.29 vs -1.83) and the reduced efflux amount of BER (i.e., ER: 1.71 vs 12.11). Furthermore, BLCC demonstrated a relative bioavailability of 410 % in comparison to the original BER, due to notably enhanced intestinal permeability of BLCC and its continuous dissolution in simulated intestinal fluid. BLCC has the potential to tailor the dissolution behavior, improve intestinal permeability, and boost the bioavailability of BER. This indicates that the cocrystal strategy holds promise as an effective approach to improving the oral absorption and bioavailability of active pharmaceutical molecules with low permeability during drug development.

Dehydration and Rehydration Mechanisms of Pharmaceutical Crystals: Classification Of Hydrates by Activation Energy

Dehydration strongly influences the stability of hydrate drug substances. Consequently, the ability to predict dehydration of crystalline hydrate using the intermolecular interactions of water molecules contained in the crystals is essential for drug development. The conventional method employed to predict the propensity for dehydration uses the dehydration temperature, which is related to how tightly water molecules are bound in the crystal lattice. However, it is difficult to predict the dehydration propensity of a particular hydrate using only the dehydration temperature because other kinetic factors affect dehydration behavior, such as intermolecular interactions, and drug-substance-to-water molar ratio in a hydrate. In this study, we explored the use of the dehydration activation energy E_a and rehydration behavior to classify 11 pharmaceutical hydrates into three classes according to their kinetic behavior related to the thermodynamic factors of hydrates. There is good agreement between these classes and hydrate crystal structures determined from single-crystal X-ray diffraction, and thus, the classification reflects their crystal structural features. We compared E_a to the dehydration temperatures for each class and found that E_a plays a crucial role and is better than the temperature for quantitative differentiation of the dehydration propensities in these hydrates.

Puerarin-Na Chelate Hydrate Simultaneously Improves Dissolution and Mechanical Behavior

Puerarin monohydrate (PUEM), as the commercial solid form of the natural anti-hypertension drug puerarin (PUE), has low solubility, poor flowability, and mechanical properties. In this study, a novel solid form as PUE-Na chelate hydrate was prepared by a reactive crystallization method. Crystal structure analysis demonstrated that PUE-Na contains PUE^-, Na⁺, and water in a molar ratio of 1:1:7. It crystallizes in the monoclinic space group P2₁, and Na⁺ is linked with PUE^- and four water molecules through Na⁺ ← O coordination bonds. Another three crystal water molecules occupy channels along the crystallographic b-axis. Observing along the b-axis, the crystal structure features a distinct tubular helix and a DNA-like twisted helix. The complexation between Na⁺ and PUE^- in aqueous solution was confirmed by the Na⁺ selective electrode, indicating that PUE-Na chelate hydrate belongs to a type of chelate rather than organic metal salt. Compared with PUEM, PUE-Na exhibited a superior dissolution rate (i.e., ∼38-fold increase in water) owing to its lower solvation free energy and clear-enriched exposed polar groups. Moreover, PUE-Na enhanced the tabletability and flowability of PUEM, attributing to its better elastoplastic deformation and lower-friction crystal habit. The unique PUE-Na chelate hydrate with significantly enhanced pharmaceutical properties is a very promising candidate for future product development of PUE.

Crystallization of Cyclophosphamide Monohydrate During Lyophilization

The purpose of this study was to investigate the phase behavior of cyclophosphamide (CPA) during various stages of lyophilization, with special emphasis on obtaining crystalline CPA monohydrate (CPA-MH) in the lyophilized product. Subambient differential scanning calorimetry and low-temperature X-ray diffractometry (LTXRD) were used to study the phase behavior of CPA solution (3.7% w/v). In situ lyophilization in LTXRD chamber was used to monitor the phase transitions occurring during the drying stages. Finally, the implications of these findings were confirmed by freeze-drying the aqueous solution in a laboratory-scale freeze-dryer. The results suggested that CPA remains amorphous during freeze concentration, with a T_g' of -50°C. However, its crystallization as CPA-MH can be induced by annealing the frozen solution between -5°C and -10°C. In situ lyophilization in LTXRD showed that the CPA-MH crystallized during annealing, rapidly dehydrated during primary drying, thereby causing structural collapse. The dehydration of CPA-MH can be prevented by lowering the escaping tendency of water molecules from the crystal lattice of CPA-MH by maintaining the chamber pressure to 300, 400, or 500 mTorr. This study highlights the relationship of process parameters used during lyophilization with the solid form of lyophilized CPA.