Introduction

The goal of any sterilization process is to destroy microorganisms present on a preparation or object. Ensuring that tools and materials are free of microorganisms is essential for the safety and effectiveness of pharmaceutical products. An object or preparation is considered “sterile” when it can be statistically certified that the probability of it NOT being sterile is equal to or less than 1 in 1,000,000, introducing the concept of SAL (Sterility Assurance Level).

Sterilization methods can be divided into two categories:
Physical Methods: moist heat, dry heat, microfiltration, ionizing and UV radiation, ultrasound.
Chemical Methods: sterilizing chemicals, vapors or gases, substances in gas-plasma state.
The most commonly used methods in the pharmaceutical world are saturated steam sterilization (autoclaves, SIP) and dry heat sterilization (ovens). This article will explore these processes, explaining the concepts of lethality, D-value, and Z-value, and providing references to existing regulations.

Saturated Steam Sterilization

Saturated steam sterilization is considered the best and most effective method by most guidelines for sterilizing objects and preparations in pharmaceutical departments. This process exploits the one-to-one correspondence between temperature and pressure of saturated steam to eliminate microorganisms and spores..

Autoclaves

Autoclaves are devices that use saturated steam under pressure to sterilize materials. The typical process involves exposing objects to 121°C for 15-20 minutes or 134°C for 3-5 minutes. Autoclaves are widely used for their effectiveness and reliability.

Sterilization In Place (SIP)

SIP is a saturated steam sterilization process used to sterilize equipment and piping without disassembling them. This method is particularly useful for complex systems and large production plants.

Dry Heat Sterilization

Dry heat sterilization uses hot air to eliminate microorganisms. It is a physical process conducted in the absence of moisture. This method is less common than saturated steam sterilization but is useful for materials that cannot be sterilized with steam, such as powders and oils.

Ovens

Dry heat sterilization ovens operate at high temperatures, typically between 160°C and 180°C, for prolonged periods (2 to 4 hours). Also known as “Pasteur ovens,” they are often cube-shaped, double-walled cabinets. Heat is generated by built-in electric resistances that heat the air in the chamber. This method is effective for heat-resistant and non-porous materials.

Concepts of Lethality, D-Value, and Z-Value

Lethality

Lethality is a measure of the effectiveness of a sterilization process in destroying microorganisms. It is often expressed as F0, which represents the equivalent sterilization time at 121°C.

D-Value

The D-value (decimal reduction time) is the time required to reduce the microorganism population by a factor of 10 (90%) of the initially present microorganisms. This value is crucial for determining the effectiveness of a sterilization process.

Z-Value

The Z-value represents the temperature change needed to modify the D-value by a factor of 10. This value helps understand the thermal resistance of microorganisms and optimize sterilization processes.

Reference Regulations
Regulations governing sterilization processes in pharmaceutical departments include:
• ISO 17665: This standard provides requirements for steam sterilization of healthcare products.
• EN 285: Specifies requirements for steam autoclaves used for sterilizing medical devices.
• ISO 11140: Defines requirements for chemical indicators used in sterilization processes.

Conclusions

Saturated steam and dry heat sterilization are essential processes in pharmaceutical production departments to ensure the safety and effectiveness of products. Understanding the concepts of lethality, D-value, and Z-value is fundamental to optimizing these processes. Existing regulations provide a framework to ensure that sterilization processes are effective and comply with quality standards.