Abstract: The invention relates to a composition comprising an effective amount of a peptides antibiotic at least one hydrophilic degradable microsphere comprising a crosslinked matrix, and a pharmaceutically acceptable carrier for administration by injection, the crosslinked matrix being based on at least a) between 10 mol % and 90 mol % of hydrophilic monomer of general formula (I); b) between 0.1 and 30 mol % of a cyclic monomer of formula (II); and c) between 5 mol % and 90 mol % of one degradable block copolymer cross-linker, wherein the degradable block copolymer crosslinker is linear or star-shaped and presents (CH2?(CR11))-groups at all its extremities and wherein the degradable block copolymer crosslinker has a partition coefficient P of between ?3 and 11.20. The invention also relates to such a composition for use for preventing and/or treating infectious diseases, in particular mammal infectious diseases, by local delivery.