Disclosed is a prolonged release pharmaceutical dosage form comprising a plurality of coated beads , each comprising a granule, a first layer coated on the granule comprising hydromorphone , naloxone , an antioxidant compound and a chelatmg compound and a second layer coated on the first layer comprising a prolonged release agent. The dosage form has improved stability and dissolution properties. Also disclosed is the use of a combination of an antioxidant , such as sodium metabisulfite , and a chelatmg agent , such as EDTA , to improve the stability and/or dissolution properties of a prolonged release dosage form comprising hydromorphone and naloxone.
