Compounding pharmacies are an essential part of the healthcare system, as they provide customized medications to meet the specific needs of patients. However, the preparation of sterile compounds requires a high level of cleanliness, and the design of the cleanroom is a critical factor in achieving this. One crucial aspect of cleanroom design is the use of cascading differential pressure, which ensures that the air flows in a controlled manner to minimize the risk of contamination.
Differential pressure is the difference in pressure between two adjacent spaces, and in cleanroom design, it is used to control the direction of airflow. A positive pressure differential means that air flows from the cleanest area to the less clean area, while a negative pressure differential means that air flows from the less clean area to the cleanest area.
Cascading differential pressure refers to the use of multiple pressure differentials in a series of spaces. For example, in a compounding pharmacy cleanroom, the cleanest area is the ISO-Class 5 (formerly known as Class 100) sterile compounding area, where the medication is prepared in a secondary engineering control (SEC). The SEC is placed in a cleanroom called the buffer area For non-hazardous rooms United States Pharmacopeia (USP) General Chapter <797> Pharmaceutical Compounding - Sterile Preparations states the buffer area should have a positive pressure differential of at least 0.02 inches WC compared to the anteroom.
The anteroom is the space between the outside and the buffer area, and it serves as a transition space where personnel can don and doff personal protective equipment (PPE) before entering the buffer area. The anteroom should have a should have a positive pressure differential of at least 0.02 inches WC compared to the non-classified area.
USP Chapter <800> Hazardous Drugs -Handling in Healthcare Setting is a set of guidelines developed to ensure safe handling of hazardous drugs (HDs) in healthcare settings. For a hazardous drug buffer area, the room should maintain negative pressure with respect to surrounding areas to prevent the escape of HDs into other parts of the facility. Specifically, the pressure differential should be at least -0.01 inces of WC and no more than -0.03 inces of WC. This helps to ensure the safety of compounding technicians, patients and environment by minimizing risk of exposure to HDs.