Question

the use of a drug to prevent imminent infection of a person at risk is called

Explanation:

In the field of Medicine and Health (a subfield of Natural Science), the use of a drug to prevent imminent infection in a person at risk is known as prophylaxis (or preventive treatment). This concept is related to preventing disease before it occurs, especially in those exposed or at risk.

Answer:

Prophylaxis (or Preventive Treatment)