Liquid pharmaceutical formulation for the prolonged release of AP comprising an aqueous colloidal suspension of dynamic viscosity at 20°C less than or equal to 1000 mPa.s, based on micrometric particles, having a size of between 1 and 70 μm as measured in a test T, comprised of polymer and multivalent ions of opposite polarity to that of the polymer PO, wherein the polymer PO - is a water-soluble, biodegradable, amphiphilic copolymer, wherein said copolymer is a polyamino acid whose main chain is made up of aspartic residues or glutamic residues, at least some of these residues carrying hydrophobic groups and ionizable hydrophilic groups at least partially ionized, - and spontaneously forms a colloidal suspension of nanoparticles in water, at pH = 7.0, under isotonic conditions, said nanoparticles being capable of associating spontaneously and non-covalently with at least one active principle, at pH = 7.0, under isotonic conditions; - the multivalent ions of said formulation are: - of valency less than or equal to 4, preferably divalent ions, trivalent ions or mixtures thereof, - of opposite polarity to that of the ionizable groups GI of the polymer PO, - in an amount such that the ratio r, measured in a test M, is comprised between 0.3 and 10, preferably between 0.6 and 5.0 and even more preferably between 0.8 and 3.0, said ratio r being defined by the formula r = n × IM GI, where - n is the valency of said multivalent ions, - is the molar concentration of multivalent ions, - is the molar concentration of ionizable groups GI. - is a water-soluble, biodegradable, amphiphilic copolymer, wherein said copolymer is a polyamino acid whose main chain is made up of aspartic residues or glutamic residues, at least some of these residues carrying hydrophobic groups and ionizable hydrophilic groups at least partially ionized, - and spontaneously forms a colloidal suspension of nanoparticles in water, at pH = 7.0, under isotonic conditions, - the multivalent ions of said formulation are: - of valency less than or equal to 4, preferably divalent ions, trivalent ions or mixtures thereof, - of opposite polarity to that of the ionizable groups GI of the polymer PO, - in an amount such that the ratio r, measured in a test M, is comprised between 0.3 and 10, preferably between 0.6 and 5.0 and even more preferably between 0.8 and 3.0, said ratio r being defined by the formula r = n × IM GI, where - n is the valency of said multivalent ions, - is the molar concentration of multivalent ions, - is the molar concentration of ionizable groups GI. - of valency less than or equal to 4, preferably divalent ions, trivalent ions or mixtures thereof, - of opposite polarity to that of the ionizable groups GI of the polymer PO, - in an amount such that the ratio r, measured in a test M, is comprised between 0.3 and 10, preferably between 0.6 and 5.0 and even more preferably between 0.8 and 3.0, said ratio r being defined by the formula r = n × IM GI, where - n is the valency of said multivalent ions, - is the molar concentration of multivalent ions, - is the molar concentration of ionizable groups GI. - n is the valency of said multivalent ions, - is the molar concentration of multivalent ions, - is the molar concentration of ionizable groups GI.