A synergistic pharmaceutical composition is administered parenterally, comprising an effective amount antibacterial of at least two antibacterial agents which are chemically incompatible, wherein a) a first antibacterial agent is vancomycin or a pharmaceutically acceptable salt of this, b ) a second antibacterial agent is ceftriaxone or a pharmaceutically acceptable salt thereof, c) said first and said second antibacterial agents are present in a predetermined weight ratio of 1: 4 to 4: 1, preferably 1: 3 to 3: 1, and more preferably 1: 2 to 2: 1 together with d) a chemical vector to mediate the compatibility of said first antibacterial agent and said second antibacterial agent to provide stability to the composition, which is the L-arginine in the range of 35% to 75% of the combined weight of said first and second antibacterial agents, e) said pharmaceutical composition is supplied as a dry powder premix list pa ra injection after reconstitution in a suitable carrier f) for use as an antimicrobial therapy fixed dose combination to a mammal, including humans, provided that such combination therapy does not encompass the administration of two or more therapeutic agents as part of separate monotherapy regimens of that result in sequential or simultaneous treatment.Una composición farmacéutica sinérgica, que se administra por vía parenteral, que comprende una cantidad eficaz como antibactericida de a menos dos agentes antibacterianos que son químicamente incompatibles, en donde a) un primer agente antibacteriano es la vancomicina o una sal farmacéuticamente aceptable de esta, b) un segundo agente antibacteriano es ceftriaxona o una sal farmacéuticamente aceptable de esta, c) dicho primer y dicho segundo agentes antibacterianos están presentes en una relación en peso predeterminada de 1:4 a 4:1, preferentemente 1:3 a 3:1, y con mayor preferencia 1:2 a 2:1 junto con d) un vector químico, para mediar la compatibilidad de dicho primer agente antibacteriano y dicho segundo
