Medical Injections do not break the fast based on the opinion of the majority of the schools of thought: The things that break the fast are those which are entered into the body via natural openings either from the mouth, nose or the anus.
The same ruling applies for eye drops. Eye drops do not break the fast even if you feel like you can taste them in your mouth- according to the majority of the scholars. This ruling has been generalized on all types of injections such as those administered under the skin, muscular injections and Intravenous injections.