Pneumonia, a lower respiratory tract infection by bacteria or viruses, results in high morbidity rate. Pneumonia resists to multiple drug therapy, lowering the treatment success^1-3. Gram negative pathogen Pseudomonas aeruginosa is a significant cause of pneumonia. Doripenem presents a good potential both for the gram positive and gram negativepathogens⁴. Also, pulmonary delivery offers an effective approach to orally or parenterally delivered antibiotics. The pulmonary administration, which is less invasive, may reduce side effects, increasing patient compliance. This study develops biodegradable microparticles, designed to deliver doripenem into the pulmonary tract. To produce large porous microparticles, three different methods were used: double emulsion-solvent evaporation, ionotropic gelation-lyophilization and ionotropic gelation-spray drying. Double emulsion-solvent evaporation method did not generate spherical particles. Subsequently, ionotropic gelation method was applied to different types of chitosan, whereby spherical particles were generated. In order to overcome the aggregation problem, spray drying was utilized, this way the optimum size distribution is obtained. Thus achieved encapsulation efficiency range reaches up to 80% level. The average particle size of doripenem-loaded microparticles ranged between 3.820-6.984µm (F9-F17). Doripenem-loaded microparticles suitable for pulmonary administration have been characterized and they are undergoing optimization studies in in vitro release.