In this work, the supercritical antisolvent (SAS) coprecipitation of zein with amoxicillin trihydrate (AMOXI) and ampicillin sodium salt (AMPO, two commonly used broad-spectrum antibiotics is proposed. In order to precipitate composite microspheres with controlled dimensions, the proper conditions, in terms of operating temperature and zein/antibiotic ratio, were identified. In the case of amoxicillin trihydrate, at 90 bar, 40 degrees C, 50 mg/mL and zein/AMOXI ratio equal to 20/1, spherical microparticles with mean diameter equal to 0.65 +/- 0.51 mu m were successfully produced. In the case of ampicillin sodium salt, at 90 bar, 50 degrees C, 50 mg/mL and zein/AMPI ratio equal to 5/1, spherical microparticles with mean diameter equal to 9.0 +/- 5.7 mu m were precipitated. Drug release analyses revealed that the release of the antibiotics was significantly delayed, confirming that zein/antibiotic coprecipitates obtained by SAS can be used for controlled-release formulations.