The present invention relates to novel microparticles formed of amphiphilic polyamino acids which transport active principle(s), AP(s), in particular protein and peptide active principle(s), and to novel modified-release pharmaceutical formulations comprising said AP microparticles. Microparticles of amphiphilic polyamino acid (PO) may include at least one AP (associated noncovalently) which spontaneously form a colloidal suspension of nanoparticles in water, at pH 7.0, under isotonic conditions. The microparticles may be obtained by atomization of a solution or colloidal suspension of PO comprising at least one AP, may have a size of between 0.5 and 100 microns, and may be dispersible in colloidal suspension.
