5.2 Category 2 Beyond-Use Dating: Sterile vs. Nonsterile Starting Components

Architectural Mandates for Category 2 Compounding

To qualify for Category 2 Beyond-Use Dating, preparations must be compounded within a fully classified cleanroom suite:

• Primary Engineering Control: An ISO Class 5 PEC (LAFW, Class II BSC, CAI, or CACI).
• Secondary Engineering Control: An ISO Class 7 buffer room.
• Ante-Room: An ISO Class 8 ante-room (for positive-pressure suites) or an ISO Class 7 ante-room (for negative-pressure hazardous drug suites).
• Compounding personnel must satisfy initial 3-trial gloved fingertip testing with zero CFUs and semiannual competency re-qualifications.

The USP <797> 2023 Category 2 Default BUD Matrix

Under the 2023 revision of USP <797>, Category 2 BUDs are assigned based on three critical variables: starting component sterility, sterilization method, and sterility testing status.

Comprehensive Category 2 BUD Table

Analysis of Component Sterility & Sterilization Impact

1. Sterile vs. Nonsterile Starting Components

When an active pharmaceutical ingredient (API) is introduced as a bulk nonsterile powder (e.g., baclofen powder for intrathecal pump compounding, or alum powder for bladder irrigation), bioburden may be high. Even if the solution is then sterilized by 0.22-micron filtration, USP <797> limits the untested BUD to 1 day at room temperature or 4 days refrigerated. Nonsterile components bring bioburden and bacterial endotoxin risk, and the CSP's sterility has not been confirmed by testing.

2. Terminal Sterilization vs. Aseptic Processing

Terminal sterilization, such as steam under pressure (USP <797> gives 20 to 60 minutes at $121^\circ\text{C}$ and 15 psi as an example, depending on load), destroys microorganisms inside the sealed final container, achieving a Sterility Assurance Level (SAL) of $10^{-6}$ (less than one non-sterile unit per million). Because terminal sterilization is fundamentally more robust than aseptic assembly, untested terminally sterilized CSPs receive 14 days room temperature and 28 days refrigerated BUD allowances.

3. Stability Limitations

Regardless of the table values above, the BUD may never exceed what stability supports. The Table 13 limits are microbiological ceilings. USP <797> also requires the BUD to reflect chemical and physical stability, the container-closure system, and the shortest expiration of any component. Ampicillin is a classic example: its solutions hydrolyze within hours at room temperature, so the product labeling or a stability study, not Table 13, sets its BUD.

4. Sterility Testing Protocol & Quarantine Requirements

The longer Category 2 BUDs require a passing sterility test by USP <71> or a validated alternative that is non-inferior to it (USP <1223>). USP <71> incubates for 14 days, in Soybean-Casein Digest Medium at $20^\circ\text{C to }25^\circ\text{C}$ and Fluid Thioglycollate Medium at $30^\circ\text{C to }35^\circ\text{C}$. USP <797> allows a CSP to be dispensed before release test results are known. In that case the facility must have procedures ready to notify the prescriber immediately of a failure, recall unused CSPs, quarantine remaining stock, and check other lots (USP <797> 18.1). Many facilities hold batches until results are final whenever the clinical schedule allows.

Sterilization Modalities for Nonsterile Preparations

When nonsterile starting components are utilized in Category 2 compounding, sterilization is legally and clinically mandatory. USP General Chapter <797> recognizes three primary sterilization modalities:

1. Sterilizing-Grade Membrane Filtration

• Mechanics and Membrane Pore Size: Solutions must be passed through a certified sterilizing-grade hydrophilic membrane filter with a nominal pore rating of $0.22\,\mu\text{m}$ or $0.2\,\mu\text{m}$, certified to retain $\ge 10^7\,\text{CFU}/\text{cm}^2$ of Brevundimonas diminuta (ATCC 19146).
• Polymer Compatibility: Polyethersulfone (PES) is preferred for aqueous solutions and low protein binding; PVDF for biologics; PTFE for harsh organic solvents; and nylon for general aqueous compounding.
• Mandatory Filter Integrity Testing: Each sterilizing filter must pass the manufacturer's recommended integrity test, such as a post-use bubble point test. The bubble point pressure follows the Young-Laplace relationship ($P = \frac{4 \gamma \cos \theta}{d}$). If the filter fails, USP <797> requires the CSP to be discarded or, after the cause is investigated and a suitable filter chosen, refiltered no more than one additional time.

2. Moist Heat Sterilization (Steam Autoclaving)

• Mechanics: Destroys microorganisms by denaturing and coagulating essential proteins. USP <797> cites 20 to 60 minutes at $121^\circ\text{C}$ and $15\,\text{psi}$ as an example; the actual time depends on container volume and load. Solutions are passed through a filter of 1.2 µm or smaller before filling, to remove particles.
• Biological Validation: The effectiveness of every run or load is verified with appropriate biological indicators, such as Geobacillus stearothermophilus spores, read according to the indicator manufacturer's instructions. Physicochemical indicators support this, and a calibrated recorder documents each cycle.

3. Dry Heat Sterilization & Depyrogenation

• Sterilization: Used for heat-stable, moisture-sensitive items such as oils and dry powders, usually in an oven at $160^\circ\text{C}$ or higher. Lower temperatures must be shown to be effective. Each run is verified with Bacillus atrophaeus biological indicators.
• Depyrogenation: Destroys bacterial endotoxin on glassware and other heat-stable items, typically at about $250^\circ\text{C}$. The cycle must be shown, initially and then at least annually, to achieve at least a 3-log endotoxin reduction using Endotoxin Challenge Vials (ECVs).