USP General Chapter 797 sets the standards for compounding sterile preparations – the facilities, the air, the people, the procedures and the dating. It applies to hospital pharmacies, compounding pharmacies, infusion centers, physician offices and any other setting where a sterile preparation is compounded rather than bought finished.
A large share of the USP 797 material online is out of date, and in a way that matters. The chapter was substantially revised, with the current version official since 1 November 2023. The revision did not merely tighten numbers – it replaced the organizing framework. Any guide still describing “low, medium and high risk” compounding is describing a structure that no longer exists.
What the 2023 revision changed
The single largest change is the replacement of risk levels with CSP Categories. Under the previous structure, a preparation was classified by how much manipulation it involved and how likely contamination was. Under the current structure, a preparation is classified by the conditions under which it was made and what testing supports it – which then determines how long it may be used.
| Withdrawn framework | Current framework | |
|---|---|---|
| Organizing principle | Low / medium / high risk, based on manipulation complexity | Category 1, 2 and 3 CSPs, based on compounding environment and supporting testing |
| What sets the dating | Risk level plus storage temperature | Category, sterility testing, and whether a sterilization method was applied |
| Segregated compounding | Limited recognition | Explicit – Category 1 may be prepared in an unclassified segregated compounding area |
| Terminology | Risk level | Category, PEC, SEC, SCA, C-SCA |
The practical consequence for anyone specifying or building a facility is that the category you intend to compound determines the room you have to build, and that decision has to be made before design rather than discovered during inspection.
The three CSP categories and what each demands
| Category 1 | Category 2 | Category 3 | |
|---|---|---|---|
| Where it may be prepared | An ISO 5 primary engineering control sited in an unclassified segregated compounding area (SCA) | ISO 5 PEC inside a classified cleanroom suite – ISO 7 buffer room with an ante-room | As Category 2, with additional controls throughout |
| Beyond-use dating | Shortest – limited to hours at controlled room temperature, somewhat longer refrigerated | Longer, and varies with sterility testing, sterilization method and storage temperature | Longest permitted, and only with the full additional control set |
| Sterility testing | Not required | Required for the longer dating options | Required |
| Endotoxin testing | Not required | Situational | Required for the extended dating |
| Garbing and competency | Standard requirements | Standard requirements | More stringent, with more frequent competency reassessment |
| Typical use case | Urgent-use and short-dated preparations | The mainstream hospital and compounding pharmacy model | Batch production with extended dating |
The point most often missed in planning: Category 3 is not simply Category 2 with a longer date stamped on it. It carries a different testing regime, tighter personnel qualification and a documentation burden that continues for the life of the operation. Facilities routinely build to Category 2 and then discover their intended dating requires Category 3 controls they did not budget for.
The engineering controls, in the language a builder needs
USP 797 uses its own vocabulary, and translating it into construction terms is where most of the confusion sits.
| Term | What it is | Classification | Notes for design |
|---|---|---|---|
| PEC – primary engineering control | The device the compounding actually happens in: laminar airflow workbench, biological safety cabinet, compounding aseptic isolator | ISO 5 | This is the critical zone. Everything else exists to protect it |
| SEC – secondary engineering control | The room the PEC sits in – the buffer room | ISO 7 | Requires the ante-room to be classified as well |
| Ante-room | The transition space where garbing and hand hygiene occur | ISO 7 or ISO 8 depending on what it opens into | ISO 7 is required where it opens into a negative-pressure buffer room |
| SCA – segregated compounding area | An unclassified space containing an ISO 5 PEC, used for Category 1 only | Unclassified room, ISO 5 PEC | Restricted to Category 1 dating. Cheapest route, shortest dates |
| C-SCA / C-SEC | The containment equivalents, for hazardous drug compounding | Per USP 800 | Negative pressure, externally vented |
The airflow and pressure requirements are where a cleanroom contractor earns or loses the project:
| Parameter | Requirement | Why it is set that way |
|---|---|---|
| Air changes, classified rooms | At least 30 ACH of HEPA-filtered air in ISO 7 buffer and ante-rooms | Recovery after a disturbance, not steady-state cleanliness alone |
| Pressure, non-hazardous buffer room | Positive, at least 0.020 in w.c. relative to the ante-room | Keeps the dirtier adjacent space out of the cleaner one |
| Pressure, hazardous (USP 800) | Negative, 0.01 to 0.03 in w.c., externally vented | Protects personnel from the drug – the opposite objective, and a hard conflict to design around |
| Air pattern into the PEC | Unidirectional, undisturbed | Any air movement that disrupts first-air across the critical site defeats the entire arrangement |
| Surfaces | Smooth, impervious, free from cracks and crevices, non-shedding, cleanable and resistant to the disinfectants used | Sporicidal agents are aggressive – material selection is a durability problem as well as a cleanability one |
The positive-versus-negative conflict is the single most common design failure in this space. A pharmacy that compounds both non-hazardous and hazardous preparations needs a positive-pressure buffer room and a negative-pressure containment room, both fed and controlled correctly, with an ante-room arrangement that serves each without letting either compromise the other. Retrofitting the second one into a suite designed only for the first is usually more expensive than building both at the outset, because it disturbs the pressure cascade of the whole suite.
USP 797 against USP 800: related, not interchangeable
| USP 797 | USP 800 | |
|---|---|---|
| What it protects | The preparation – sterility of the CSP | The people and the environment – exposure to hazardous drugs |
| Pressure regime | Positive relative to less clean spaces | Negative, externally vented |
| Applies when | A preparation is compounded sterile | A hazardous drug is handled, sterile or not |
| Overlap | Both apply simultaneously to a sterile hazardous preparation, and their objectives pull in opposite directions | Resolved by containment ventilation and room arrangement, not by choosing one |
Where both apply, they are not alternatives and neither overrides the other. The engineering answer is a containment primary engineering control inside a negative-pressure containment room, with the sterility objective met by the PEC and the containment objective met by the room – which is exactly why these suites are more demanding to build than either standard alone suggests.
Monitoring, cleaning and personnel: the ongoing obligations
A compliant room is a starting condition, not an achievement. The chapter imposes continuing obligations that a facility carries for as long as it compounds, and these are where inspections tend to land.
- Certification of the engineering controls at defined intervals – airflow, HEPA integrity, room classification and pressure differentials, verified by measurement rather than by assumption.
- Viable air and surface sampling on a defined schedule, with action levels and a written response when they are exceeded. The response plan is as important as the sampling.
- Sporicidal disinfection of classified surfaces at least monthly, in addition to routine daily cleaning. Sporicidal agents are hard on materials, which is why surface selection is a design decision.
- Personnel competency – garbing observation, gloved fingertip and thumb sampling, and media-fill testing, reassessed on a defined cycle that is more frequent for Category 3.
- Continuous pressure differential monitoring with a record. A gauge nobody reads is not monitoring.
Two of these have direct construction consequences that are cheap to build in and expensive to retrofit: certification requires accessible test ports and known filter locations, and pressure monitoring requires sensors, tubing runs and a recording device. Both are trivial during fit-out and disruptive afterwards.
What this means if you are building or renovating
The sequence that avoids the common failures is short and rarely followed:
- Decide the category first. Category 1 in a segregated area, Category 2 in a cleanroom suite, or Category 3 with the full control set. This decision sets the entire scope, and reversing it later means rebuilding.
- Decide whether hazardous drugs are in scope, now or within the life of the facility. Adding USP 800 containment later disturbs the pressure cascade of the whole suite.
- Size the air handling for 30 ACH minimum in every classified room, with filter loading margin – not at the clean-filter point. Our cleanroom air change calculator converts room dimensions into airflow, filter count and the ceiling-coverage check.
- Resolve the pressure cascade on paper across every door in the suite, including the failure cases, before anything is built.
- Design in the verification – test ports, sensor locations, monitoring and recording – so certification is a measurement exercise rather than an excavation.
USP 797 is a compendial chapter, not a federal regulation in itself, but it is enforceable through state boards of pharmacy and is commonly adopted directly into state rules – which is what gives it practical force. Confirm the position in your own state, because adoption and timing vary.
Related guides and tools
- Cleanroom classifications and ISO 14644 – what ISO 5, 7 and 8 actually mean and how they are verified.
- Cleanroom air change and HEPA calculator – airflow, filter count and whether they fit the ceiling.
- What is a cleanroom – the fundamentals.
- Cleanroom design and construction – if you need the suite built and certified.
- Glossary of cGMP process equipment terms.
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Frequently asked questions
What is USP 797?
USP General Chapter 797 sets the minimum standards for compounding sterile preparations – the facilities and engineering controls, air quality, personnel training and competency, cleaning and disinfection, environmental monitoring, and how long a preparation may be used. It applies wherever a sterile preparation is compounded rather than purchased finished, including hospital and compounding pharmacies, infusion centers and physician offices.
Did USP 797 change, and what changed?
Yes. The revised chapter became official on 1 November 2023 and replaced the previous risk-level structure entirely. Compounded sterile preparations are now classified as Category 1, 2 or 3 based on the environment they were prepared in and the testing that supports them, rather than as low, medium or high risk based on manipulation complexity. Guidance still describing risk levels is describing a framework that no longer exists.
What are Category 1, 2 and 3 CSPs?
Category 1 preparations are made in an ISO 5 primary engineering control located in an unclassified segregated compounding area, and carry the shortest beyond-use dating. Category 2 preparations are made in an ISO 5 control inside a classified cleanroom suite and can carry longer dating depending on sterility testing and storage. Category 3 permits the longest dating but requires an additional control set including sterility and endotoxin testing and more stringent personnel qualification.
What ISO class does a USP 797 cleanroom need?
The primary engineering control – the hood, cabinet or isolator where compounding happens – must be ISO 5. For Category 2 and 3, that control sits inside an ISO 7 buffer room, with an ante-room classified ISO 7 or ISO 8 depending on what it opens into; an ante-room opening into a negative-pressure buffer room must be ISO 7. Category 1 allows the ISO 5 control to sit in an unclassified segregated compounding area.
How many air changes per hour does USP 797 require?
At least 30 air changes per hour of HEPA-filtered air in classified rooms. Note that this is a genuine requirement of the chapter, which distinguishes it from air change figures in general cleanroom design, where ACH is a design convention rather than a specification and ISO 14644-1 classifies on particle counts instead.
What pressure differential does USP 797 require?
A non-hazardous buffer room must be positive relative to the ante-room by at least 0.020 inches water column. Hazardous drug compounding under USP 800 requires the opposite – negative pressure between 0.01 and 0.03 inches water column, with external venting. Where both apply, the conflict is resolved by containment ventilation and room arrangement rather than by choosing between them.
What is the difference between USP 797 and USP 800?
They protect different things. USP 797 protects the preparation, keeping it sterile, which drives positive pressure relative to less clean spaces. USP 800 protects personnel and the environment from hazardous drug exposure, which drives negative pressure and external venting. Both apply simultaneously to a sterile hazardous preparation, and neither overrides the other.
What is the difference between a PEC and an SEC?
The primary engineering control is the device compounding occurs in – a laminar airflow workbench, biological safety cabinet or compounding aseptic isolator – and it must maintain ISO 5 conditions at the critical site. The secondary engineering control is the room containing it, normally an ISO 7 buffer room. The PEC protects the preparation; the SEC protects the PEC.
Can I compound without a cleanroom?
Only Category 1 preparations, and only in a segregated compounding area containing an ISO 5 primary engineering control. The trade is dating: Category 1 beyond-use dates are the shortest permitted, measured in hours at controlled room temperature. It is a legitimate model for urgent-use compounding and unworkable for anything needing extended dating.
Is USP 797 legally enforceable?
Not as a federal regulation in its own right, but it has practical force because state boards of pharmacy commonly adopt it directly into state rules and inspect against it. Accreditation bodies also assess against it. Because adoption and effective dates vary between states, confirm the position in the state where you operate rather than assuming the compendial date applies.
How often must the cleanroom be certified?
Engineering controls must be certified at defined intervals, covering airflow, HEPA filter integrity, room classification and pressure differentials, verified by measurement. Environmental monitoring, including viable air and surface sampling, runs on its own schedule with defined action levels and a written response when they are exceeded. Building in accessible test ports and known filter locations makes certification a measurement exercise rather than an excavation.
What surfaces are acceptable in a USP 797 cleanroom?
Surfaces must be smooth, impervious, free from cracks and crevices, non-shedding and cleanable, and they must withstand the disinfectants used on them. That last requirement is the one that drives material selection, because sporicidal agents are required at least monthly and are aggressive – a surface that cleans well but degrades under repeated sporicidal application will fail within the life of the facility.