Final answer:
The most commonly used needle gauge to draw up medications from a single-use vial is 21 gauge.
Step-by-step explanation:
The needle gauge that is most commonly used to draw up medications from a single-use vial is 21 gauge.
The gauge of a needle refers to its diameter, and a lower gauge number indicates a larger needle.
A larger gauge needle allows for a quicker withdrawal of medication from the vial, which is useful in clinical settings where time is of the essence.