Final answer:
The appropriate instruction regarding vaginal antifungal drugs is to abstain from sexual intercourse until the treatment has been completed and the infection has resolved.
Step-by-step explanation:
The appropriate instruction regarding vaginal antifungal drugs is option a. "Abstain from sexual intercourse until the treatment has been completed and the infection has resolved." This is important because engaging in sexual intercourse during treatment can spread the infection or make it worse. It is important to complete the entire course of treatment to ensure that the infection is fully resolved.