Controlled release system of an active ingredient and method of preparation

Controlled release system of an active ingredient comprising at least (a) a polymer matrix hydrolytically degradable generating acidic compounds and (b) at least one complex between an active principle provided with at least an electrostatic charge and a polyelectrolyte associated to complex the active ingredient, oppositely charged, said complexing sensitive to acids stable at pH 7.4 and at lower pH degradable 7, formed by stoichiometric matching loads being solid complex.