USP 797 is a set of national standards that governs how pharmacies and healthcare facilities prepare sterile medications. Published by the United States Pharmacopeia (USP), it covers everything from the physical environment where compounding happens to how staff must dress, wash their hands, and prove their technique is safe. Millions of sterile medications are compounded each year in the U.S., and these standards exist to prevent contamination, infection, and incorrect dosing.
The chapter’s full title is “Pharmaceutical Compounding — Sterile Preparations,” and it applies to any medication that must be sterile: injections, IV infusions, eye injections, and spinal injections. Hospitals, compounding pharmacies, and other healthcare settings that prepare these medications are all expected to follow it.
Why USP 797 Exists
Sterile compounding carries real risk. If bacteria, fungi, or particulate matter gets into a medication that goes directly into a patient’s bloodstream, eye, or spinal canal, the consequences can be severe, including life-threatening infections. USP 797 sets minimum quality standards to reduce those risks at every step of the process: the room where compounding takes place, the equipment used, the training staff receive, and how long a compounded medication can be stored before it’s considered unsafe.
The chapter was last significantly updated in 2008, with a revised version published on June 1, 2019. After a long period of legal challenges and delays, the revised compounding chapters (including 797) reached official status on November 1, 2023.
The Three Categories of Sterile Preparations
The revised version of USP 797 organizes compounded sterile preparations (CSPs) into three categories based on the environment they’re made in, the level of quality testing they undergo, and how long they can be stored. The higher the category, the stricter the requirements and the longer the medication’s shelf life.
Category 1
Category 1 preparations are typically made in a segregated compounding area, which is a designated space with a defined perimeter that contains specialized equipment but does not need to meet full cleanroom standards. Because the environment is less controlled, these preparations have the shortest allowable storage times: up to 12 hours at room temperature or 24 hours in a refrigerator. This category suits facilities that compound in smaller volumes and use the medications quickly.
Category 2
Category 2 preparations require a cleanroom suite, a much more controlled environment. The compounding equipment must sit inside a buffer room that meets ISO Class 7 air cleanliness standards (meaning extremely low levels of airborne particles), with an anteroom meeting ISO Class 8 standards. These rooms maintain positive air pressure so that cleaner air always flows outward, pushing contaminants away from the compounding area.
Storage times for Category 2 are significantly longer. When all starting ingredients are already sterile, the preparation can be stored for up to 4 days at room temperature, 10 days refrigerated, or 45 days frozen. If any nonsterile ingredient is used, those limits drop to 1 day at room temperature, 4 days refrigerated, or 45 days frozen.
Category 3
Category 3 is the most rigorous tier. These preparations undergo sterility testing (and endotoxin testing when applicable) and must meet additional requirements for staff qualifications, sterile garbing, use of sporicidal disinfectants, and environmental monitoring. The cleanroom environment requirements are at least as strict as Category 2, and the added testing allows for the longest possible storage times. This category is designed for facilities that compound in larger batches or need extended shelf life.
Cleanroom and Equipment Standards
Regardless of category, all sterile compounding must take place inside a primary engineering control (PEC), which is a device like a laminar airflow workbench or compounding isolator that provides an ISO Class 5 environment. ISO Class 5 is the cleanest air classification required by the standard, allowing no more than 3,520 particles (0.5 microns or larger) per cubic meter of air.
For Category 2 and Category 3 preparations, the PEC must be housed inside a cleanroom suite. The buffer room (where compounding happens) is ISO Class 7, and the anteroom (where staff wash, gown up, and stage supplies) is ISO Class 8. Both rooms are kept at positive pressure relative to the areas outside them. Any presterilization work for these categories must also be done in at least an ISO Class 8 environment, using containment devices to minimize airborne contamination.
For Category 1, the PEC can be placed in a segregated compounding area that doesn’t need to meet ISO classifications, though the space must have a defined perimeter and be restricted to compounding activities.
Personnel Training and Garbing
USP 797 requires that anyone who compounds sterile medications follow a specific sequence of hand hygiene and garbing. Staff must wash their hands and put on personal protective equipment in a prescribed order, and the process of putting garb on and taking it off cannot happen in the same area at the same time. Sterile gloves must be donned in a classified room or segregated compounding area, not in an uncontrolled hallway or general pharmacy space.
Each facility must write its own standard operating procedures (SOPs) that spell out the exact garbing order. Beyond dressing properly, compounders must demonstrate aseptic technique through competency testing. This involves performing a simulated compounding procedure using growth media instead of actual drugs. If bacteria grow in the finished product, the compounder fails and must retrain before compounding again. These evaluations are repeated on a regular schedule to ensure skills don’t lapse over time.
Beyond Use Dates
One of the most practically important elements of USP 797 is the beyond use date (BUD), the deadline after which a compounded sterile preparation should not be used. BUDs are not the same as manufacturer expiration dates. They reflect the risk of contamination and degradation based on how and where the medication was made.
The limits vary by category and storage temperature:
- Category 1: 12 hours at room temperature, 24 hours refrigerated
- Category 2 (all sterile ingredients): 4 days at room temperature, 10 days refrigerated, 45 days frozen
- Category 2 (any nonsterile ingredient): 1 day at room temperature, 4 days refrigerated, 45 days frozen
- Category 3: Longer BUDs are possible because sterility testing provides additional assurance
These limits mean that a hospital pharmacy compounding in a segregated area (Category 1) must use or discard its preparations within hours, while a facility with a full cleanroom suite and sterility testing program can prepare medications days or weeks in advance.
How USP 797 Relates to USP 800
USP 797 focuses on protecting the sterility of the medication. A companion standard, USP 800, focuses on protecting the people who handle hazardous drugs, such as certain chemotherapy agents. When a sterile preparation also involves a hazardous drug, both chapters apply simultaneously. The facility must meet 797’s cleanroom requirements to keep the product sterile and 800’s containment requirements to keep staff safe. In practice, this often means a separate negative-pressure buffer room for hazardous compounding, so that air flows inward (containing fumes) rather than outward.
Who Must Follow USP 797
State boards of pharmacy are the primary enforcers of USP 797. Most states incorporate USP standards into their pharmacy regulations, making compliance a legal requirement for licensure. Accreditation organizations and federal agencies also reference USP 797 when evaluating hospitals and compounding facilities. Any setting that prepares sterile medications, whether a large hospital pharmacy, an outpatient surgery center, or a compounding pharmacy shipping preparations across state lines, is expected to meet these standards.