Preparation of CYA Eye Drops

In comparison to the referenced Cystadrops^®, a compounded eye drop formulation containing the same amount of CYA was prepared from the available compounds that are officially on the positive list of the National Institute of Pharmacy and Nutrition, Hungary (Table 1). Along with being on the positive list, hydroxyethyl cellulose (viscosity: 250–400 mPa·s, Ph.Hg. VIII) acts as a demulcent by relieving eye inflammation, irritation, and dryness [23 (link)]. The applied polymer concentration enabled sterile filtration. The preparation of the solution was conducted in a laminar air flow cabinet under aseptic conditions consisting of four main steps: (1) preparation of the buffer solution, (2) mixing of hydroxyethylcellulose into a portion of the buffer solution to produce a viscous solution, (3) dissolution of the active substance and other excipients in the remaining buffer solution, and (4) mixing of the two solutions followed by sterile filtration through a sterile polyethersulfone (PES) filter membrane of 0.22 µm pore diameter and 25 mm diameter (Stericup^®, Merck-Millipore, Darmstadt, Germany).