Role of dispersion enhancer selection in the development of novel tratinterol hydrochloride dry powder inhalation formulations

Tratinterol hydrochloride (TH) is a new long-acting bronchodilator with strong β2 adrenoceptor stimulation activity. The aim of this study was to design a new carrier-based dry powder inhalation (DPI) formulation for TH and to investigate the effect of dispersion enhancers on the aerosol performance of TH in vitro. To this end, coarse lactose was used as a carrier. TH was micronized by using a jet mill and blended with the carrier to obtain a reference DPI formulation. Commercial magnesium stearate (MgSt) as received, micronized MgSt (MgSt-M), and fine lactose (FL) were used as the dispersion enhancers and formulated with the micronized TH (TH-M) and the carrier as DPI formulations. The obtained DPI formulations were characterized using dynamic light scattering (DLS), X-ray powder diffraction (XRPD), thermal analysis, powder rheometer, and Raman microscopy. A next generation pharmaceutical impactor (NGI) was used to evaluate the aerodynamic performance of the dry powders. The results showed that TH-M was in an inhalable particle size range, and based on the XRPD and thermal analysis, the solid form of TH-M did not change compared to the starting materials. The NGI results showed that the fine particle fraction (FPF) of TH could be increased with the addition of MgSt and FL as dispersion enhancers in the reference formulation. In addition, the FPF of TH could be increased with a decrease in the particle size of MgSt or an increase in the amount of FL. A combination of MgSt-M and FL could further improve the aerosol performance of TH. Raman spectroscopic imaging confirmed the spatial location of MgSt and TH at the surface of the carrier. This study demonstrates that TH could be formulated into carrier-based dry powder formulation for inhalation using coarse lactose as the carrier. The dual strategy based on using both MgSt and FL as dispersion enhancers improved the aerosol performance of a novel TH dry powder formulation.