Abstract: The full quaternisation of DEAE‐dextran was successfully attempted and an application of the quaternised product was suggested. Commercial DEAE‐dextran was reacted with iodomethane at 60°C in the presence of NaOH. The raw product was purified by dialysis, during which the iodide ion was replaced by chloride. N‐methylation and O‐methylation resulted from the reaction. A second methylation step produced no further changes in the molecule. Alkalimetry indicated the absence of amino groups in the methylated polymer molecule, thus testifying to a complete quaternisation. N‐acetylcysteine (AcCy) was neutralised with the polymer in the hydroxide form, thus obtaining the methyl DEAE‐dextran salt of AcCy (Me‐DEAE‐dextran/AcCy), whereby an ophthalmic formulation for the treatment of the dry eye syndrome was prepared. For comparison, the neutral AcCy salt of commercial DEAE‐dextran (DEAE‐dextran/AcCy) was prepared. The AcCy content in Me‐DEAE‐dextran/AcCy was higher than in DEAE‐dextran/AcCy (23 vs 13%), while the viscosity of a solution containing the salt concentration corresponding to the therapeutic AcCy concentration (4%w/v) was lower with the former compared to the latter salt (20.5 vs 23.9 mPa s). Both solutions were ipotonic (245 mOsm/kg), whereas the commercial Tirocular® is strongly hypertonic (900 mOsm/kg) and irritant.
