A. A.Yas, and Ali Al - Jipouri. “Preparation and Evaluation of Inhalable Sustained Release Sildenafil Citrate Solid Lipid Microparticles Dispersions”. Global Journal of Medical Research, vol. 14, no. B5, Mar. 2014, pp. 1-5, https://medicalresearchjournal.org/index.php/GJMR/article/view/729.