ABSTRACT
Solid dispersion, a dispersion system in which drug molecules are highly dispersed in carrier materials, has been commonly used to improve the solubility and dissolution rate of poorly soluble drugs. The miscibility between drug and carrier is crucial to improve the dissolution performance and stability of solid dispersion. Therefore, the selection of carrier types and the optimization of drug loading are very important. In the current study, the solubility parameter method and Flory-Huggins theory were used to predict the miscibility between olaparib (OLP) and different carriers (VA64, Soluplus, Plasdone S630 and Kollidon K29/32). Besides, the carrier material with good miscibility was experimentally screened by differential scanning calorimetry (DSC). The optimum of drug-carrier ratio was further performed based on the miscibility phase diagram of drug and carrier. Theoretical calculation and experimental evaluation showed that the miscibility of OLP and VA64 was the best, and the drug loading of 30% could meet the requirements of large drug loading and physical stability. Polarizing light microscope, X-ray powder diffraction, DSC and laser confocal Raman spectroscopy exhibited that OLP was amorphous form in the solid dispersion system. Powder dissolution test demonstrated that the solid dispersion showed significantly enhanced dissolution rate in comparison to crystalline OLP. In this study, theoretical calculation and experimental evaluation were used to screen the types of carriers and optimize the drug loading, which provides an efficient strategy for the selection of carrier and the amount used in solid dispersion.
ABSTRACT
Compared with crystalline drugs, their amorphous forms present long-range disordered molecular arrangements, and often exhibit higher apparent solubility and dissolution. However, several small molecule amorphous drugs may exhibit gelation phenomenon during the dissolution process, and show abnormal dissolution behavior with significantly lower dissolution than crystalline drugs. The current study aims to discover the relationship between the gelation of amorphous drugs and their abnormal dissolution, and further explore the internal gelation mechanism. Amorphous simvastatin (SIM), carvedilol (CAR), and irbesartan (IRB) were prepared by melt cooling method and characterized via X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FT-IR). Gel formation causes the dissolution of these three amorphous drugs to be significantly lower than their crystalline state. The formed gels were characterized as three-dimensional dense network structures by scanning electron microscope (SEM). Furthermore, amorphous SIM, CAR and IRB showed the critical gel temperature at 8-15 ℃, 25-30 ℃ and 45-50 ℃, and amorphous CAR and IRB showed the critical gel pH at 1 and 0.25. The mechanism of gel formation was proposed to be closely related to the transformation of amorphous drugs into the supercooled liquid state (as the important driving force) and the protonation induced self-assembling under acidic conditions. In addition, the wettability and properties of amorphous drugs also affect the formation of gelation.
ABSTRACT
Tadalafil (TD), a phosphodiesterase-5 inhibitor for the treatment of erectile dysfunction, has a low oral bioavailability due to its extremely poorly aqueous solubility. The aim of this study was to enhance its solubility and dissolution by coamorphization with dapoxetine (DP), a selective serotonin reuptake inhibitor to manage premature ejaculation. Coamorphous TD-DP (molar ratio, 1:1) was prepared by solvent-evaporation method and characterized by differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD) and Fourier transform infrared spectroscopy (FTIR). The supersaturated dissolution of TD from coamorphous TD-DP was investigated in various aqueous media and compared to that of crystalline TD. In addition, physical stability of coamorphous system was also evaluated under the conditions of 40℃/75% relative humidity (RH) and 25℃/60% RH for 90 days. DSC thermogram and PXRD pattern indicated the formation of the coamorphous TD-DP. In comparison to original TD crystal, the dissolution of TD from coamorphous system were significantly enhanced in various media (water, 0.01 mol·L-1 HCl and pH 4.5 phosphate buffer). In addition, no crystallization phenomenon of the prepared coamorphous system was observed until 90 days' storage under 25℃/60% RH. However, when temperature and humidity were increased to 40℃/75% RH, the coamorphous TD-DP was recrystallized easily.