USP <797> Cleanroom Requirements
The facility design requirements behind a USP <797> compliant cleanroom, and what it takes to build a sterile compounding room that keeps passing certification.
USP General Chapter <797> sets the standards for compounding sterile preparations in the United States. The revised chapter became official on November 1, 2023, and it changed the way pharmacy cleanrooms are designed, classified, and certified. If your sterile compounding room was built to the previous chapter, some of what you know is now out of date.
This page states the USP <797> cleanroom requirements as they stand in 2026: the ISO classification of each room, the airflow and pressure each one has to hold, and the testing that proves it. It is written for compounding directors, chiefs of pharmacy, facility managers, and the engineers who have to turn the chapter into a room.
What changed in the 2023 revision
Four changes matter most to anyone planning or renovating a space.
- Risk levels became categories. Low, medium, and high risk are gone. Compounded sterile preparations are now Category 1, Category 2, or Category 3, and the category determines both the beyond-use date and the facility you need.
- Beyond-use dates were rewritten. They are now tied to category, storage temperature, and whether sterility testing was performed, rather than to risk level alone.
- Category 3 was created. It permits substantially longer beyond-use dates in exchange for stricter facility controls, more frequent environmental monitoring, and additional personnel qualification.
- Facility requirements were tightened and made explicit. Air changes, pressure differentials, surfaces, and sink placement are stated in the chapter rather than left to interpretation.
The three categories and their beyond-use dates
The category being compound determines the room you need. This is the first decision in any USP <797> project, and it is worth settling before anything is drawn.
|
Category |
Where it is compounded |
Room temperature |
Refrigerated |
Frozen |
|---|---|---|---|---|
|
Category 1 |
ISO 5 primary engineering control in a segregated compounding area |
12 hours |
24 hours |
Not applicable |
|
Category 2 |
ISO 5 primary engineering control inside a classified cleanroom suite |
4 days |
10 days |
45 days |
|
Category 2 with sterility testing |
ISO 5 primary engineering control inside a classified cleanroom suite |
45 days |
60 days |
90 days |
|
Category 3 |
Cleanroom suite meeting the additional Category 3 controls |
90 days |
120 days |
180 days |
Beyond-use dates are maximums. Product stability, sterility testing results, and your own validation can shorten them. Category 2 dates vary with the starting components and the sterilization method used; the values shown are the common cases.
The practical read: if you need a beyond-use date longer than 12 hours, you need a classified cleanroom suite. That single fact drives most of the capital cost of a sterile compounding project.
The classification chain
USP <797> builds cleanliness in layers. Air gets cleaner as you move toward the preparation itself, and each layer has a job.
- ISO 5 primary engineering control. The laminar airflow workbench, biological safety cabinet, or isolator where the preparation is directly exposed. This is the only place the sterile product is open to the air.
- ISO 7 buffer room. The classified room that houses the primary engineering control. It protects the ISO 5 environment from the rest of the building.
- ISO 8 ante-room. The transition space where staff gown and materials are staged. It protects the buffer room. The ante-room must be ISO 7, not ISO 8, when it opens into a negative pressure buffer room.
Each layer is defined by a particle limit from ISO 14644-1, so an ISO 7 room means the same thing to a certifier in Ohio as it does to one in Osaka.
- The particle limits behind each ISO class are on our ISO 14644 page.
Secondary engineering control requirements
The following table summarizes the secondary engineering control requirements used to guide the design of sterile compounding spaces:
|
Requirement |
Segregated compounding area |
Ante-room |
Buffer room |
|---|---|---|---|
|
ISO classification |
Unclassified |
ISO 8 |
ISO 7 |
|
HEPA air supply |
Not required |
Required at ceiling |
Required at ceiling |
|
Air changes per hour |
Not specified |
20 minimum |
30 minimum |
|
Differential pressure |
Not applicable |
Greater than 0.02 in. w.c. (greater than 5 Pa) |
Greater than 0.02 in. w.c. (greater than 5 Pa) |
|
Temperature |
20 °C (68 °F) or cooler |
20 °C (68 °F) or cooler |
20 °C (68 °F) or cooler |
|
Relative humidity |
Below 60% |
Below 60% |
Below 60% |
|
External ventilation |
Not required |
Not required |
Not required |
|
Hand-washing sink |
Within 1 m of the primary engineering control, inside or close to the area |
Inside or outside the ante-room, in a clean space either way |
Not permitted |
|
Line of demarcation |
Not required |
Required, separating the clean side from the dirty side |
Not required |
Pressure is measured relative to adjacent unclassified space, positive in a non-hazardous suite. At least 15 of the buffer room’s 30 air changes must come from ceiling-mounted HEPA filters.
The segregated compounding area, and when you can use one
Not every pharmacy needs a cleanroom suite. A segregated compounding area is an unclassified space containing an ISO 5 primary engineering control, and it is the lower-cost path for facilities with modest compounding volume.
The tradeoff is the beyond-use date. Everything compounded in a segregated compounding area is Category 1, which means 12 hours at room temperature or 24 hours refrigerated. For a hospital preparing doses for same-day administration, that is often enough. For a pharmacy that batches ahead, it is not.
A segregated compounding area also has rules of its own. It must be separated from other activity, it cannot be placed in a high-traffic area or near anything that generates particles, and the hand-washing sink must sit within one meter of the primary engineering control.
Cleanroom certification, and why dynamic conditions matter
A USP <797> pharmacy cleanroom must be certified at least every six months, and recertified after any change that could affect its performance. Certification covers airflow, HEPA filter integrity, particle counts, pressure differentials, and smoke pattern studies.
The requirement that catches facilities out is that testing must be performed under dynamic operating conditions. That means staff working, equipment running, doors moving, and material flowing, as the room actually operates. A room certified empty and quiet tells you very little about the room in use.
We see two failures repeatedly. The first is a buffer room that holds its pressure with the door closed and loses it every time a cart goes through, because the air handling has no capacity in reserve. The second is a smoke study that shows clean laminar flow in an empty cabinet and turbulence around the operator’s arms in a real one. Both are design problems, and both are cheaper to solve on paper than after commissioning.
Surfaces, finishes, and flow
The chapter is specific about the physical room. Ceilings, walls, floors, doors, door frames, fixtures, shelving, work surfaces, counters, and cabinets in a classified area must be smooth, impervious, free from cracks and crevices, and non-shedding, so they can be cleaned and disinfected.
- Junctures between ceiling and wall, and between wall and floor, must be sealed. Floors need coving to the sidewall, or a caulked juncture.
- Ceiling panels must be caulked to the support frame. Light fixture lenses must be smooth, flush-mounted, and sealed. Any other penetration through a ceiling or wall must be sealed.
- Surfaces have to survive the cleaning agents, disinfectants, and sporicidal agents used on them. This is where cheap finishes fail first, usually within two years.
- The buffer room cannot contain a sink or a floor drain.
- Overhangs and ledges should be minimized. Where they exist, they must be easy to clean.
Questions we are asked most often
The answer determines the category, and the category determines the room. Same-day doses administered within 12 hours can be prepared in a segregated compounding area. Anything batched, stored, or shipped needs a classified cleanroom suite. Non-sterile starting ingredients push you to Category 3.
ISO 5 in the primary engineering control, ISO 7 in the buffer room at 30 air changes per hour, and ISO 8 in the ante-room at 20 air changes per hour. Maintain more than 0.02 in. w.c. positive between the ante-room and the buffer room, keep the space at 20 °C or cooler, and hold relative humidity below 60%.
Certification every six months under dynamic operating conditions, covering airflow, HEPA integrity, particle counts, pressure, and smoke pattern studies. Environmental monitoring for viable particles runs on its own schedule, more frequently for Category 3.
Through a maintenance program that treats the room as a system: filter changes on a known schedule, pressure monitoring with alarms and a visual display, cleaning with agents the surfaces can tolerate, and a record that a certifier can follow. Most rooms that fail did not fail suddenly.
Changes to equipment, processes, layout, or facility conditions require reassessment, and often recertification before compounding resumes. Adding a second cabinet to a buffer room changes its airflow. Replacing a door changes its pressure. Plan changes with the same care as the original build.
Not the same room, no. Hazardous drug compounding requires a negative pressure buffer room and external venting, which USP 797 alone does not. A facility doing both needs separate buffer rooms, and the ante-room serving the negative pressure room must be ISO 7.
- We explain how the two chapters fit together on our USP <800> page.
Related standards
Sterile compounding sits inside a wider set of standards. These pages cover the ones that most often apply alongside USP <797>.
Important information
The information on this page is intended for general educational purposes only. It does not constitute legal, regulatory, engineering, or professional advice, and it should not be relied upon as a determination of compliance for any particular facility, application, or jurisdiction.
QleanAir makes reasonable efforts to keep this information current. Standards and regulations change, and we do not guarantee that every figure here reflects the most recent version of every applicable requirement. Before making design, construction, testing, operational, or compliance decisions, consult the current USP requirements and seek advice from qualified professionals.
Last reviewed: September 2026.
For most up-to-date information, please visit: USP Compounding Compendium Online One-Year Subscription (includes USP <795>,<797>,<800>)