Final answer:
PECs must maintain an ISO classification, have unidirectional airflow, and comply with USP 797 regulations to ensure a sterile environment for medication preparation in pharmacies.
Step-by-step explanation:
The student's question is about Primary Engineering Controls (PECs), which are critical in pharmacies for ensuring a sterile environment for the preparation of medications. The PECs must meet specific criteria including maintaining an ISO classification, which refers to the International Organization for Standardization's standards for air quality in cleanrooms.
The blank would be filled with the specific ISO class number that dictates the maximum allowable particles in the air. Furthermore, PECs must have unidirectional airflow, meaning the air flows in a single direction to avoid mixing of clean and dirty air, which is a requirement for maintaining sterility of the preparations. These requirements comply with the standards outlined in USP 797, which is a regulation that provides guidelines on the compounding of sterile preparations, thereby ensuring patient safety.