Hospital pharmacy compounding rooms (USP 797 and 800)

Sterile compounding pharmacies prepare intravenous medications, chemotherapy, total parenteral nutrition and other preparations that must be free of microbial contamination. Many also handle hazardous drugs that pose risks to pharmacy staff. The HVAC system is central to both goals: it creates the classified environment that protects the preparation and the negative pressure environment that contains hazardous drugs.

In the United States, requirements come from USP General Chapter 797 (sterile compounding) and USP 800 (hazardous drugs). In Canada, the National Association of Pharmacy Regulatory Authorities (NAPRA) publishes model standards for sterile compounding of non-hazardous and hazardous preparations, which draw heavily on USP and are adopted or adapted by provincial pharmacy regulators. Hospital facilities are also designed to CSA Z317.2. This guide explains the HVAC requirements in general terms. Always confirm current requirements with the provincial regulator and the applicable edition of each standard.

Key spaces

The ISO 14644 classification guide explains ISO classes.

Non-hazardous sterile compounding (USP 797)

The revised USP 797, official since November 2023, sets these main HVAC requirements for non-hazardous compounding suites:

• Air changes. The ISO 7 buffer room needs at least 30 air changes per hour (ACH) of HEPA-filtered supply air, of which at least 15 ACH must come from the HVAC system through ceiling HEPA filters. The PEC may contribute the remainder if it runs continuously. An ISO 7 ante-room needs at least 30 ACH, and an ISO 8 ante-room at least 20 ACH.
• Pressure. The buffer room must be positive to the ante-room, and the ante-room positive to the unclassified area, by at least 0.020 in. w.c. (about 5 Pa).
• HEPA supply in the ceiling with low-wall returns, distributed to sweep air away from the PEC.
• Temperature and humidity. USP 797 recommends 20 C (68 F) or cooler and relative humidity below 60 percent in classified areas, and the beyond-use dating assumptions relate to these conditions.
• Continuous monitoring of pressure differentials, with documented review each day compounding occurs.

Hazardous drug compounding (USP 800)

Hazardous drugs, such as many chemotherapy agents, must be compounded in a containment primary engineering control (C-PEC), such as a Class II biological safety cabinet or compounding aseptic containment isolator, located in a containment secondary engineering control (C-SEC).

For a sterile hazardous drug suite, the main HVAC requirements are:

• Negative pressure buffer room. The C-SEC buffer room is ISO 7, at least 30 ACH, and negative to adjacent spaces by 0.010 to 0.030 in. w.c. (about 2.5 to 7.5 Pa).
• Positive ISO 7 ante-room. The ante-room is ISO 7 and positive to the unclassified area, acting as a barrier between the negative buffer room and the corridor.
• External exhaust. The C-PEC and the room must be exhausted to the outdoors, not recirculated.
• C-SCA alternative. For limited compounding, a C-SCA is unclassified, negative 0.010 to 0.030 in. w.c., externally exhausted and provides at least 12 ACH.
• Storage rooms for hazardous drugs are negative pressure with at least 12 ACH and external exhaust.

NAPRA model standards for hazardous sterile preparations set comparable requirements, with some differences in detail. Hospitals should check the version their provincial regulator has adopted.

Pressure arrangement

A typical suite combining non-hazardous and hazardous compounding has a single positive ISO 7 ante-room serving both a positive non-hazardous buffer room and a negative hazardous drug buffer room. The pressure arrangement then looks like this:

1. Corridor (reference).
2. Ante-room: positive to corridor.
3. Non-hazardous buffer room: positive to ante-room.
4. Hazardous drug buffer room: negative to ante-room.

The positive ante-room protects the hazardous room from corridor contamination while preventing hazardous drug residue from escaping. Achieving all relationships at once requires careful airflow offset design and tight room construction. See cleanroom pressurization cascades.

HVAC design considerations

Dedicated systems

Compounding suites usually need a dedicated air handling system, or at least dedicated terminal units with HEPA filtration, so that pressures and air changes stay stable regardless of the rest of the hospital. Systems serving them should run continuously, with emergency power where the facility's risk assessment requires it.

Biological safety cabinet exhaust

Class II type A2 cabinets are often connected with a canopy (thimble) connection, while type B2 cabinets are hard ducted with total exhaust. Hard-ducted cabinets are sensitive to exhaust fan performance, and loss of exhaust must stop compounding with an alarm. Exhaust fans should be on the roof, discharge vertically at high velocity and be located away from air intakes. In Canada, cabinets are certified to NSF/ANSI 49 and CSA Z316.3 guidance.

Airflow control

Pressure-independent supply and exhaust devices, such as venturi air valves or airflow-measuring terminal units, help hold the offset when exhaust from cabinets varies. Control options are compared in room pressurization control: offset vs direct pressure.

Construction

Ceilings, walls and floors must be smooth, cleanable and sealed. Penetrations for sprinklers, lights, sensors and ducts must be sealed. Pass-throughs between rooms should be interlocked. Room tightness has a direct effect on the airflow needed to hold pressure.

Temperature control

Holding 20 C or cooler in a small room with a biological safety cabinet, people and lighting often requires dedicated cooling. Gowned staff are uncomfortable in warm rooms, and higher temperatures can affect beyond-use dating.

Certification

USP 797 requires certification of classified areas and PECs before initial use and at least every six months, and after major changes. Testing commonly follows the Controlled Environment Testing Association (CETA) application guides and typically includes:

1. Airflow volume and air change rate calculations.
2. HEPA filter integrity (leak) testing.
3. Room pressure differentials.
4. Total particle counts under dynamic operating conditions.
5. Airflow visualization (smoke studies) in PECs and at doors.
6. PEC certification, including inflow and downflow velocities.

Environmental monitoring for viable airborne and surface microorganisms is also required at defined intervals. See cleanroom certification and testing.

Key takeaways

• USP 797 and 800 set HVAC requirements for sterile and hazardous drug compounding, and NAPRA model standards apply similar requirements through Canadian provincial regulators.
• ISO 7 buffer rooms need at least 30 ACH, with at least 15 ACH from ceiling HEPA filters on the HVAC system.
• Non-hazardous buffer rooms are positive by at least 0.020 in. w.c.; hazardous drug buffer rooms are negative by 0.010 to 0.030 in. w.c. and externally exhausted.
• Dedicated, continuously operating HVAC with pressure-independent airflow control keeps pressures stable.
• Certification every six months and environmental monitoring confirm ongoing compliance.