When should a first air source be established in an ISO Class 5 environment?

The first air source in an ISO Class 5 environment should be established immediately before commencing any compounding process because the integrity of the sterile environment is crucial for preventing contamination. The first air refers to the unidirectional airflow that provides a sterile environment directly over the area where sterile products are compounded.

By establishing the first air just before beginning the compounding process, you ensure that the work area is free from contaminants and that any potential sources of microbial contamination are minimized. This action maintains the required sterility levels and aligns with best practices outlined in the USP 797 guidelines, which emphasize the importance of working in a sterile environment at all times when handling sterile medications.

Setting the first air up at other times, such as after all materials are prepared or at the end of the compounding process, does not provide the same level of contamination control and could compromise the sterility of the compound being prepared. Additionally, doing so once per shift is insufficient since environmental conditions can change throughout the day, potentially affecting sterility.