Esterified cellulose ethers which comprise (i) aliphatic monovalent acyl groups or (ii) groups of the formula &mdash；C(O)&mdash；R&mdash；COOA, wherein R is a divalent aliphatic or aromatic hydrocarbon group and A is hydrogen or a cation, or (iii) a combination of aliphatic monovalent acyl groups and groups of the formula &mdash；C(O)&mdash；R&mdash；COOA, which have a viscosity of up 19 mPa·s, measured as a 10 wt % solution of the esterified cellulose ether in acetone at 20° C., and which have a weight average molecular weight Mw of at least 90,000 Dalton, are useful for preparing solid dispersions comprising drugs.
