What is an example of a common preservative used in compounding?

Boric acid is indeed a common preservative used in compounding due to its antimicrobial and antifungal properties. It effectively inhibits the growth of bacteria and fungi, making it suitable for inclusion in formulations that require preservation against microbial contamination. Its low toxicity and compatibility with various pharmaceutical compounds further enhance its usefulness in compounding practices.

In contrast, baking soda, vinegar, and salt, while having their own uses in certain formulations, do not primarily serve as preservatives. Baking soda is mainly used as a buffering agent or to adjust pH, vinegar acts as a flavoring agent and mild preservative but is less common in compounding for long-term storage, and salt is primarily a flavor enhancer or preservative in food rather than a commonly acknowledged preservative in pharmaceutical preparations. Therefore, boric acid stands out as the most relevant choice when discussing preservatives in compounding.