EVALUATION OF HIGH-MOLECULAR-WEIGHT AND LOW-MOLECULAR-WEIGHT FRACTIONS OF SODIUM HYALURONATE AND AN IONIC COMPLEX AS ADJUVANTS FOR TOPICAL OPHTHALMIC VEHICLES CONTAINING PILOCARPINE

Two low-molecular-weight fractions of sodium hyaluronate (Na-HA), denominated Hyalastin(R) and Hyalectin(R), were investigated as potential adjuvants for ophthalmic vehicles containing pilocarpine nitrate (PiN). Tests were also performed on an ionic complex (HA/PiB) prepared from hyaluronic acid (derived from Hyalastin(R)) and pilocarpine base. The performance of the vehicles under study was verified by miosis and ocular retention tests carried out on albino rabbits, against a series of reference vehicles, three of which contained a high-molecular-weight fraction of Na-Ha (Healon(R)). The group of 14 reference and test preparations exhibited Newtonian or pseudoplastic flow characteristics and encompassed a wide range of apparent viscosities (1 to 1054 mPa s). The results indicate that the HA/PiB salt and the high-MW Na-HA can significantly increase the bioavailability of pilocarpine with respect to reference vehicles of comparable viscosity: an effect that can be reasonably attributed to muco-adhesive effects. Conversely, in the present rabbit tests, the low-MW fractions of Na-HA performed poorly as adjuvants for the PiN solutions.