a method for the preparation of a bioadhesive compact matrix , which comprises the preparation of a uniform mixture of powders comprising one alkylcellulose or one hydroxy alkylcellulose and a non - water - soluble , water - swellable cross - linked polycarboxylic polymer ; the preparation of compressed units starting from such powder mixture by direct compression and finally the heating of the compressed units thus obtained to a temperature in the range of 80 - 250 ° c . for a time of 1 - 60 minutes ; the powder mixture can also comprise at least one active substance and the compressed units thus obtained are characterized by a prolonged release , and have a release kinetics of the active substance substantially of zero order in an aqueous solution at ph 4 - 8 .