The present invention relates to novel polyelectrolyte polymer particles for transporting an active principle (AP), in particular a protein and peptide active principle, and also to novel modified-release pharmaceutical formulations containing said AP microparticles. These novel AP-loaded particles release the AP over a prolonged duration of several days, or even several weeks. The invention relates, in a first aspect, to particles comprising: a) a first polyelectrolyte polymer (PE1) in the charged state, bearing side hydrophobic groups (HG), said first polyelectrolyte polymer (PE1) spontaneously forming, in water, a colloidal solution of particles at at least a value pHm of the pH between 3 and 8； b) a second polyelectrolyte polymer (PE2) of opposite polarity to that of the first polyelectrolyte polymer (PE1), said second polyelectrolyte polymer (PE2) forming, in water, a solution or a colloidal solution at at least said pHm value of the pH； c) at least one active principle (AP) combined non-covalently with the particles of the colloidal solution of the first polyelectrolyte polymer (PE1)； said particles being obtained by mixing, at a pH equal to pHm, of the first polyelectrolyte polymer (PE1) in the form of a colloidal solution of particles combined with the active principle (AP) with the second polyelectrolyte polymer (PE2) in the form of a solution or a colloidal solution. The invention also relates to the process for preparing these particles, a pharmaceutical formulation comprising such particles and a process for preparing medications.
