Sustained release therapeutic compositions

A shaped and compressed sustained release therapeutic composition comprising a therapeutically active medicament and a carrier base material, characterized by a long-lasting slow and regular incremental release of the medicament upon administration, wherein the carrier base material is hydroxypropylmethylcellulose or a mixture of hydroxypropylmethylcellulose and either up to 30% ethylcellulose or 30% sodium carboxymethylcellulose or both, and wherein the hydroxypropylmethylcellulose or the mixtures thereof have been subjected to hydrolysis and oxidation and have a carbonyl content which ranges from 0.2 to 3.0 grams/100 grams and a carboxyl content which ranges from 0.37 to 2.6 grams/100 grams, the oxidation having been carried out at about 30.degree. to 50.degree. C. in the presence of oxygen or a stream of air for a period of time sufficient to obtain the desired carbonyl and carboxyl values and the composition having incorporated therein 0.1-1.0%, based on the weight of the carrier material, of a reducing stabilizing agent which prevents undesired further oxidation and the hydrolysis having been carried out either (a) by humidification in a chamber at ambient or elevated temperature until the humidity of the chamber reaches at least 85% and the humidity is maintained for at least 12 hours or (b) by mixing the carrier base material with water and heating to a temperature of 30.degree.-100.degree. C. for at least 12 hours.