The paper examines the effects on the density of ophthalmic lamellae obtained by lyophilisation of the hydrogel of hydroxypropylmethylcellulose (HPMC 4000) in a concentration of 40 g/l due to an addition of pilocarpinium chloride or scopolaminium bromide. The density of the basic xerogel 66.4 g/l is markedly increased in the presence of 54.3 g/l pilocarpinium chloride. On the other hand, a lower concentration of 11.4 g/l scopolaminium bromide slightly decreases the density. Changes in density influence the actual concentration of the active ingredient in hydrated lamellae. Changes are marked primarily in pilocarpinium chloride where changes in the density of lyophilised ophthalmic lamellae must be paid special attention to.

        Key words: density – lyophilisation – hydroxypropylmethylcellulose – pilocarpinium chloride – scopolaminium bromide