Solid lipid discs from water-in-oil emulsion as controlled release delivery systems of highly soluble drugs

Solid lipid systems (SLSs) are widely employed to control the release of highly hydrophilic drugs, and they are, in general, obtained by solubilizing or suspending the drug within melted lipid excipients. This work proposes an advantageous strategy to modulate the drug release of a hydrophilic drug loaded into a lipid matrix using as a starting formulation a water-in-oil emulsion. Therefore, the active ingredient (metoclopramide HCl as a drug model) is solubilized in the emulsion internal phase, and some formulation and process parameters were used as variables for drug release kinetics modulation. Four lipid excipients with different chain lengths of the fatty acids (Dynasan® 114, 116, 118 and Softisan® 154) were selected as external phases by melting them and emulsifying two predefined volumes of 50 % (w/w) metoclopramide HCl aqueous solution to obtain two different drug loadings. Sixteen batches of solid lipid discs were produced by dripping each emulsion into plastic molds and solidifying in an ice bath or at room temperature. The solid lipid discs were compact after the extraction from molds and homogeneous in shape and size. The maximum percentage of residual water in the discs did not exceed 6 %, and their experimental drug content was close to the expected theoretical values. Results indicate that the drug release from the discs can be modulated by changing the percentage of the loaded drug, the length of the fatty acid chain, and the solidification conditions (room temperature or ice). This approach provides a straightforward and exploitable tool for developing other types of SLSs.