Section 2.10: Sterile Compounding: Techniques & Quality Standards

Sterile Compounding: Techniques & Quality Standards

Sterile compounding involves the preparation of compounded sterile preparations (CSPs) that must be free from microbial contaminants, pyrogens, and particulate matter. Clinical consequences of contaminated CSPs are severe, including sepsis, meningitis, and death. In Saudi Arabia, the Saudi Food and Drug Authority (SFDA) and the Saudi Commission for Health Specialties (SCFHS) enforce standards aligned with United States Pharmacopeia (USP) Chapter <797> to ensure patient safety.

USP <797> Quality Standards and Facility Design

Facility design for sterile compounding relies on maintaining strict pressure gradients and air filtration standards, measured by the International Organization for Standardization (ISO) classifications.

Air Quality Classifications (ISO Standards)

ISO classes represent the maximum allowable concentration of airborne particles per cubic meter of air (particles $\ge 0.5\text{ microns}$):

• ISO Class 5: Limit of $3,520\text{ particles/m}^3$. This is the standard required inside the Primary Engineering Control (PEC) where actual compounding takes place.
• ISO Class 7: Limit of $352,000\text{ particles/m}^3$. Required for the Buffer Room (Cleanroom) where the PEC is housed.
• ISO Class 8: Limit of $3,520,000\text{ particles/m}^3$. Required for the Anteroom, where hand washing, garbing, and component staging occur.

Primary Engineering Controls (PECs)

PECs provide the ISO Class 5 environment through High-Efficiency Particulate Air (HEPA) filters, which remove $99.97%$ of particles as small as $0.3\text{ microns}$.

1. Horizontal Laminar Flow Workbenches (LAFW)

• Airflow Direction: HEPA filter is located at the back of the hood, and air blows horizontally forward from the back toward the operator.
• Use: Non-hazardous compounding only (e.g., standard IV fluids, saline flushes).
• Safety Warning: Never use a horizontal hood for hazardous drugs (e.g., chemotherapy). The forward airflow exposes the operator to toxic aerosols.

2. Vertical Laminar Flow Workbenches & Biological Safety Cabinets (BSC)

• Airflow Direction: HEPA filter is at the top of the hood, and air blows downward. Air is drawn into grilles at the front and back of the work surface, recirculated, or exhausted.
• Use: Hazardous drug compounding (antineoplastics, hormones).
• Safety Benefit: Protects both the preparation from contamination and the operator from chemical exposure.

Essential Hood Operation Rules

• Continuous Run: Keep hoods running continuously. If turned off, run the hood for at least 30 minutes before compounding to purge the air.
• Sanitization: Clean with sterile water, then disinfect with 70% sterile Isopropyl Alcohol (IPA) using lint-free wipes. Clean from top to bottom, back to front (moving from the HEPA filter toward the operator). Never spray the HEPA filter membrane directly.
• Placement: Work at least 6 inches inside the hood. Never block "first-air" (unobstructed HEPA-filtered air) reaching critical sites (vial stoppers, syringe needles, ampule necks).

Personal Protective Equipment (PPE) & Garbing Sequence

To minimize contamination, compounding personnel must follow a strict, sequential garbing process in the anteroom, moving from "dirtiest" to "cleanest":

1. Shoe covers: Don first upon entering the anteroom.
2. Hair and beard covers: Completely tuck in all hair.
3. Face mask and eye shield: Secure tightly over the nose and mouth.
4. Hand hygiene: Wash hands and forearms up to the elbows with soap and warm water for at least 30 seconds. Clean under fingernails with a warm water nail cleaner. Dry with a lint-free towel.
5. Gown: Don a non-shedding, disposable or laundered cleanroom gown.
6. Sterile gloves: After entering the buffer room, apply alcohol-based hand rub and allow to dry. Don sterile, powder-free gloves, pulling the cuffs over the gown sleeves.
7. Sanitize gloves: Regularly spray gloves with $70%$ sterile IPA during compounding.

Sterility & Quality Control Testing

• Sterility Testing (USP <71>): Required for high-risk CSPs made in batches or with extended BUDs. Methods include membrane filtration (preferred, where drug passes through a $0.22\text{-micron}$ filter which is then incubated) and direct inoculation (adding the drug directly to culture media).
• Filter Integrity (Bubble Point Test): Measures the pressure required to force air bubbles through a fully wetted filter membrane. A lower-than-expected bubble point pressure indicates a ruptured or defective $0.22\text{-micron}$ sterilizing filter.
• Bacterial Endotoxins (Pyrogens): Gram-negative bacterial outer membranes release endotoxins that cause severe febrile reactions. The Limulus Amebocyte Lysate (LAL) test is used to detect and quantify endotoxins.

Step-by-Step Worked Compounding Calculation

A physician orders $1.5\text{ g}$ of Vancomycin IV PB in $250\text{ mL}$ of D5W to be administered over $2\text{ hours}$ to a patient. The pharmacy stock is a dry-powder vial containing $5\text{ g}$ of Vancomycin. The manufacturer's instructions state to reconstitute the $5\text{ g}$ vial with $50\text{ mL}$ of Sterile Water for Injection to yield a final concentration of $100\text{ mg/mL}$.

1. Calculate the volume of reconstituted Vancomycin solution needed for the dose: $\text{Volume (mL)} = \frac{\text{Required Dose (g)}}{\text{Concentration (g/mL)}} = \frac{1.5\text{ g}}{0.1\text{ g/mL}} = 15\text{ mL}$

2. Aseptic Procedure in Hood: Under ISO Class 5 laminar flow, the operator draws exactly $15\text{ mL}$ of reconstituted Vancomycin solution using a sterile syringe and injects it into a $250\text{ mL}$ D5W infusion bag. The bag is labeled with a Beyond-Use Date (BUD) based on stability guidelines (typically $9\text{ days}$ under refrigeration for Category 2 CSPs).