We demonstrated the difference in the distribution state of pharmaceutical ingredients between tacrolimus (TCR) original ointment and six kinds of generic medicines. Two-dimensional imaging and depth analysis using attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy and confocal Raman microscopy were used, in addition to the evaluation of pharmaceutical properties, including spreading properties, rheological properties, and amount of solvent. The solvents, such as propylene carbonate and triacetin, in TCR ointments formed liquid droplets and dispersed in hydrocarbon oils. Waxes, white beeswax and beeswax, formed other domains. Confocal Raman microscopy could detect liquid droplet size without coalescence of that on germanium or glass surfaces. The combination of ATR FT-IR and confocal Raman imaging would be a powerful tool to reveal the size and shape of liquid droplets of pharmaceutical ingredients in semisolid formulations.
Keywords: Tacrolimus ointments; confocal Raman spectroscopy; imaging analysis; rheological property.