Imaging Analysis Enables Differentiation of the Distribution of Pharmaceutical Ingredients in Tacrolimus Ointments

Assessing and Predicting Physical Stability of Emulsion-Based Topical Semisolid Products: A Review

The emulsion-based topical semisolid dosage forms present a high degree of complexity due to their microstructures which is apparent from their compositions comprising at least two immiscible liquid phases, often times of high viscosity. These complex microstructures are thermodynamically unstable, and the physical stability of such preparations is governed by formulation parameters such as phase volume ratio, type of emulsifiers and their concentration, HLB value of the emulsifier, as well as by process parameters such as homogenizer speed, time, temperature etc. Therefore, a detailed understanding of the microstructure in the DP and critical factors that influence the stability of emulsions is essential to ensure the quality and shelf-life of emulsion-based topical semisolid products. This review aims to provide an overview of the main strategies used to stabilize pharmaceutical emulsions contained in semisolid products and various characterization techniques and tools that have been utilized so far to evaluate their long-term stability. Accelerated physical stability assessment using dispersion analyzer tools such as an analytical centrifuge to predict the product shelf-life has been discussed. In addition, mathematical modeling for phase separation rate for non-Newtonian systems like semisolid emulsion products has also been discussed to guide formulation scientists to predict a priori stability of these products.

Semisolid Pharmaceutical Product Characterization Using Non-invasive X-ray Microscopy and AI-Based Image Analytics

This work reports the use of X-ray microscopy (XRM) imaging to characterize the microstructure of semisolid formulations containing multiple immiscible phases. For emulsion-based semisolid formulations, the disperse phase globule size and its distribution can be critical quality attributes of the product. Optical microscopy and light diffraction techniques are traditionally used to characterize globule size distribution. These techniques are subjected to sample preparation bias and present challenges from matrix interference and data processing. XRM imaging is an emergent technique that when combined with intelligent data processing has been used to characterize microstructures of pharmaceutical dosage forms including oral solid formulations, controlled release microspheres, and lyophilized products. This work described our first attempt to use XRM imaging to characterize two complex emulsion-based semisolid formulations, a petrolatum-based ointment with a dispersed phase comprising a hydrophilic liquid, and an oil-in-water cream. This initial assessment of technology showed that microstructure details such as globule size distribution, volume fraction, spatial distribution uniformity, inter-globule spacing, and globule sphericity could be obtained and parameterized. It was concluded that XRM imaging, combined with artificial intelligence-based image processing is feasible to generate advanced characterization of semisolid formulation microstructure through 3D visualization and parameterization of globule attributes. This technique holds promise to provide significantly richer microstructure details of semisolid formulations. When fully developed and validated, it is potentially useful for quantitative comparison of microstructure equivalence of semisolid formulations.

Effects of Manufacturing Conditions on Pharmaceutical Properties of Petrolatum Ointment-Distribution of Hydrocarbon

Petrolatum ointment, which is an oleaginous ointment, is generally produced through manufacturing processes such as melting, mixing, and cooling. In this type of semisolid formulation, the manufacturing conditions of each process are empirically known to affect the quality of the resultant preparation; however, in many cases, the details of the factors are unclear. To clearly investigate the influence of the pharmaceutical properties of petrolatum ointments, we manufactured several ointments while changing the conditions of the mixing and cooling process after melting white petrolatum. As a result, the temperature at the termination was determined to influence the pharmaceutical properties of the final product. To investigate these phenomena, each petrolatum ointment sample was examined via digital microscopy and laser Raman analysis, and the distribution of the liquid-solid parts of samples was investigated. The internal structure of the ointment sample manufactured at a mixing-stop temperature of 40 °C, the needle crystals and the spherical aggregates surrounding them appropriately coexisted, while the structure exhibited a state wherein the two were linked in a semisolid phase. Meanwhile, for the ointment sample manufactured under the lowest mixing-stop temperature of 25 °C, the liquid part and the spherical aggregates were clearly separated, indicating that the liquid part was easily separated from ointments. In addition, the distribution of the hydrocarbons among the samples was measured via GC-MS; no significant difference in chemical structure was observed. In conclusion, the internal structure of the petrolatum ointment was changed by the manufacturing conditions, and this affected the pharmaceutical properties.

Advanced Formulation Design for Topical Creams Assisted with Vibrational Spectroscopic Imaging

Vibrational spectroscopic imaging has become useful analytical tools for quality control of drug products. In this study, we applied microscopic attenuated total reflection (ATR)-IR and confocal Raman microscopy to elucidate microscopic structure of creams and for the formulation design in the development of semi-solid drug products. The model creams were prepared with prednisolone (PRD) and fluconazole (FLC) as active pharmaceutical ingredients and oily solvents such as mineral oil (MO), isopropyl myristate (IPM), benzyl alcohol (BA) and diethyl sebacate (DES). As a result of microscopic ATR-IR imaging, several domains indicating oily internal phase were observed, which had absorption around 1732 and 1734 cm^-1 derived from MO, IPM and DES. In addition, domains of BA around 1009 cm^-1 were observed at the complemental or similar position in the formulation with MO or DES, respectively. These results suggested that the creams were oil-in-water type and the distribution of domains would reflect the compatibility of the solvents. The contents of PRD and BA were determined quantitatively in each layer after the intentional separation of the creams and the results agreed well with the imaging analysis. Whereas, confocal Raman imaging allowed to visualize the distribution of the components in depth direction as well as two-dimensional plane. In particular, the Raman imaging would ensure the coexistence of FLC and BA as oily phase in the cream. From these results, the feasibility of spectroscopic imaging techniques was successfully demonstrated for the formulation design of semi-solid dosage forms.