The phrase "using up" means to use all of something or to deplete its resources. However, there are many other ways to express this idea. Some synonyms for "using up" include consuming, exhausting, depleting, draining, utilizing, and expending. These words all convey the notion of using something completely or to the point of emptiness. Other synonyms for "using up" might depend on the specific context, such as "burning through" for energy resources, "running out of" for a limited supply, or "squeezing dry" for a metaphorical resource. By using synonyms for "using up," writers and speakers can create more vivid and varied language.