Which is NOT a form of topical medication?

Topical medications are designed to be applied directly to the skin or mucous membranes for localized effects, which distinguishes them from other forms of medication. In the context of the options provided, creams, aerosol sprays, and patches are all forms of topical medications because they are applied externally and work on the surface of the skin or just beneath it.

Liquid injections, however, are typically administered through a syringe or needle into the body, usually into muscle, fat tissue, or blood vessels, rather than being applied externally. This mode of administration involves systemic effects rather than localized treatment, which is the primary characteristic of topical medications. Therefore, identifying liquid injections as not a form of topical medication is accurate, as they do not align with the intended use and application method of topical therapies.