Which preservative is noted for its use in injections?

Thimerosal is recognized for its use as a preservative in injections, particularly in vaccines. It is an organomercury compound that has been employed to prevent bacterial and fungal contamination in vaccine formulations. Its effectiveness in preserving the sterility of multi-dose vials is a key reason for its use, especially in formulations that may be exposed to air or manipulation during multiple uses.

The other options do not serve this purpose in the context of injections. Vitamin C, while an antioxidant, is not used as a preservative in vaccines or injectable formulations. Boric acid is primarily used in ocular solutions and has limited application in injections due to its potential toxicity. Isopropyl alcohol is commonly used as a disinfectant for skin preparation but does not act as a preservative within injectable products. Thus, thimerosal is the correct choice for its established role in preserving the integrity of injectable medications and vaccines.