Modulating the dehydration conditions of adefovir dipivoxil dihydrate to obtain different physical forms of anhydrate

Effect of Coformer Selection on In Vitro and In Vivo Performance of Adefovir Dipivoxil Cocrystals

PURPOSE

This study aimed to improve the in vitro dissolution, permeability and oral bioavailability of adefovir dipivoxil (ADD) by cocrystal technology and clarify the important role of coformer selection on the cocrystal's properties.

METHODS

ADD was cocrystallized with three small molecules (i.e., paracetamol (PA), saccharin (SAC) and nicotinamide (NIC)), respectively. The obtained ADD-PA cocrystal was characterized by DSC, TGA, PXRD and FTIR. Comparative study on dissolution rates among the three ADD cocrystals were conducted in water and pH 6.8 phosphate buffer. Besides, effects of coformers on intestinal permeability of ADD were evaluated via in vitro Caco-2 cell model and in situ single-pass intestinal perfusion model in rats. Furthermore, in vivo pharmacokinetic study of ADD cocrystals was also compared.

RESULTS

Dissolution rates of ADD cocrystals were improved with the order of ADD-SAC cocrystal > ADD-PA cocrystal > ADD-NIC cocrystal. The permeability studies on Caco-2 cell model and single-pass intestinal perfusion model indicated that PA could enhance intestinal absorption of ADD by P-gp inhibition, while SAC and NIC did not. Further in vivo pharmacokinetic study showed that ADD-SAC cocrystal exhibited higher C_max (1.4-fold) and AUC_0-t (1.3-fold) of ADD than administration of ADD alone, and C_max and AUC_0-t of ADD-PA cocrystal were significantly enhanced by 2.1-fold and 2.2-fold, respectively, which was attributed to its higher dissolution and improved intestinal permeability.

CONCLUSION

Coformer selection had an important role on cocrystal's properties, and cocrystallization of ADD with a suitable coformer was an effective approach to enhance both dissolution and bioavailability of ADD.

Pharmaceutical Hydrates Analysis-Overview of Methods and Recent Advances

This review discusses a set of instrumental and computational methods that are used to characterize hydrated forms of APIs (active pharmaceutical ingredients). The focus has been put on highlighting advantages as well as on presenting some limitations of the selected analytical approaches. This has been performed in order to facilitate the choice of an appropriate method depending on the type of the structural feature that is to be analyzed, that is, degree of hydration, crystal structure and dynamics, and (de)hydration kinetics. The presented techniques include X-ray diffraction (single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD)), spectroscopic (solid state nuclear magnetic resonance spectroscopy (ssNMR), Fourier-transformed infrared spectroscopy (FT-IR), Raman spectroscopy), thermal (differential scanning calorimetry (DSC), thermogravimetric analysis (TGA)), gravimetric (dynamic vapour sorption (DVS)), and computational (molecular mechanics (MM), Quantum Mechanics (QM), molecular dynamics (MD)) methods. Further, the successful applications of the presented methods in the studies of hydrated APIs as well as studies on the excipients' influence on these processes have been described in many examples.

Crystallographic and Energetic Insights into Reduced Dissolution and Physical Stability of a Drug-Surfactant Salt: The Case of Norfloxacin Lauryl Sulfate

A commonly used pharmaceutical surfactant, sodium lauryl sulfate (SLS), has been reported to reduce the dissolution rate of drugs due to the formation of a less soluble drug-lauryl sulfate salt. In this study, we provide direct crystallographic evidence of the formation of salt between SLS and norfloxacin (NOR), [NORH⁺][LS^-]·1.5 H₂O. The available crystal structure also enables the use of the energy framework to gain an understanding of the structure-property relationship. Results show that the hydrophobic methyl groups in SLS dominate the surfaces of the [NORH⁺][LS^-]·1.5 H₂O crystals, resulting in the increased hydrophobicity and reduced wettability by aqueous media. Moreover, an analysis of molecular environments and energy calculations of water molecules provides insight into the stability of [NORH⁺][LS^-]·1.5 H₂O with variations in the relative humidity and temperature. In summary, important pharmaceutical properties, such as solubility, dissolution, and thermal stability, of the drug-surfactant salt [NORH⁺][LS^-]·1.5 H₂O have been characterized and understood based on crystallographic and energetic analyses of the crystal structure.