We present vancomycin-loaded dual-function injectable hydrogel that delivers antibiotic locally suitable for treatment of infections in avascular or necrotic tissues. The syringe-deliverable gels were developed using polydextran aldehyde and an inherently antibacterial polymer N-(2-hydroxypropyl)-3-trimethylammonium chitosan chloride along with vancomycin. The antibiotic was primarily encapsulated via reversible imine bonds formed between vancomycin and polydextran aldehyde in the hydrogel which allowed sustained release of vancomycin over an extended period of time in a pH-dependent mariner. Being inherently antibacterial, the gels displayed excellent efficacy against bacteria due to dual mode of action (killing bacteria upon contact as well as by releasing antibiotics into surroundings). Upon subcutaneous implantation, the gel was shown to kill methicillin-resistant Staphylococcus aureus (>99.999%) when bacteria were introduced directly into the gel as well as at distal site from the gel in a mice model. These materials thus represent as novel noninvasive drug-delivery device suitable for local antibiotic therapy.