The invention relates to a pH-sensitive polymer which is a (meth)acrylate
copolymer composed of 20 to 65% by weight acrylic and/or methacrylic acid
units and 80 to 35% by weight units of C.sub.1- to C.sub.18-alkyl esters
of (meth)acrylic acid, characterized in that it has a molecular weight in
the range from 1 000 to 50 000 g/mol, and brings about at least 60%
haemolysis at pH 5.5, and less than 5% haemolysis at pH 7.4, in a
concentration of 150 .mu.g/ml in a cytotoxicity test with human red blood
cells. The invention further relates to the use of the pH-sensitive
polymer as carrier for pharmaceutically effective biomolecules or active
pharmaceutical ingredients and as ingredient of corresponding dosage
forms.
