Development of Spray-Dried Sildenafil Citrate -α-cyclodextrin Complexes for Use in Dry Powder Inhalers

Background: Sildenafil citrate is a drug used in the treatment of pulmonary hypertension. The development of sildenafil citrate complexed with α-cyclodextrin as dry powder inhaler (DPI) should enhance its solubility in the lung. Methods: Sildenafil citrate was dissolved with α-cyclodextrin solution at pH 4.5 to obtain inclusion complexes. The complex solution was spray-dried to make spheroidal powder. The sildenafil DPI formulations were mixed with coarse lactose and fine lactose as carriers and then filled in capsule no. 2. Three different ratios of course to fine lactose were used (1:1 (#1), 2:1 (#2) and 3:1 (#3)) to optimize the performance and aerosol properties. The fine particle fraction (FPF), mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD) were used to evaluate the in vitro drug delivery performance in the lung by in vitro. Results: The proportion of sildenafil in formulations #1, #2, #3 was 100.2% ± 0.1%, 100.1% ± 0.2% and 98.9% ± 0.1%, respectively. The aerosol properties of the best formulation (#2) were as follows: an ED of 85.5 ± 0.5%, an FPF of 56.6 ± 2.3%, an MMAD of 3.2 ± 0.6 μm and a GSD of 1.02±0.01. Conclusion: Sildenafil citrate complexed with α-cyclodextrin was successfully developed for a DPI by using coarse and fine lactose monohydrate in a 2:1 ratio.