Injectable antibiotic formulations and their methods of use

An injectable, ready-to-use, oil-based, non-aqueous veterinary pharmaceutical composition comprising as the only antibiotic in the composition, penethamate (PNT) hydroiodide, and at least one oily vehicle selected from one or more of the group consisting of ethyl oleate, medium chain triglycerides, and triacetin, wherein the ratio of the PNT hydroiodide to the at least one oily vehicle is 1:1 to 1:4 w/v, wherein the concentration of PNT hydroiodide is between 15-55% w/v, and wherein the viscosity of the composition is below 3000 mPas at a temperature of 20° C. and a shear rate of 1/s when measured with a cup cylinder method, and wherein the penethamate hydroiodide shows substantially no degradation after storage of the composition over 180 days at 30 degrees Celsius.