Principle and Working of Autoclave in Pharmaceuticals

Sterilization is an essential operation in pharmaceutical manufacturing, particularly when it comes to sterile products. Impacting directly upon patient safety, contamination control is of utmost importance at sterile product facilities. Within the entire spectrum of methods used to sterilize materials for use in the pharmaceutical industry, autoclaving (steam sterilization) is presently accepted to be the most reliable and widely used method of sterilizing equipment, components, garments and media, as well as other material.

The use of saturated steam (in an autoclave) is the basis for the extensive use of autoclaves within sterile manufacturing/packaging areas where its ability to provide effective microbial destruction of materials with excellent penetration capability is accepted.

Regulatory authorities review the performance of autoclaves as a critical point of review when performing aseptic processing and therefore require that pharmaceutical manufacturers maintain validated and properly controlled systems in accordance with GMP; thus creating sterility and regulatory compliance assurance to the pharmaceutical manufacturer.

Pharmaceutical professionals must possess thorough knowledge of the principle, working mechanism, critical parameters and operational challenges associated with an autoclave in order to ensure sterility assurance and regulatory compliance.

What is an Autoclave?

In 1879, Charles Chamberland developed the autoclave as a sterilization alternative to open flame techniques. While autoclaves (also called steam sterilizers in some settings) exist in varying shapes and sizes, the basic principle of autoclave sterilization is the same.

Autoclaves are pressure vessels that are used to sterilize materials with moist heat (saturated steam) under high temperature and high pressure for an established exposure period or holding time. The purpose of autoclaving is to kill:

• Bacterial cells
• Bacterial fungal cells
• Bacterial viral cells
• Bacterial spores

Moist heat (steam) is considered the most reliable means of sterilization because the proteins and enzymes in microorganisms will be denatured by the heat, at a sufficiently elevated temperature (above 121 degrees Celsius) during contact with the moisture.

Pharmaceuticals frequently utilize the autoclave in the sterilization process of:

• Stainless steel equipment
• Glass containers
• Rubber closure caps
• Clothing or garb
• Culture media
• Filter units
• Processing equipment

Basic Principle of Autoclave

The basic operating principle of an autoclave is to use saturated steam at a high temperature (121 to 134 degrees Celsius) and at a certain point of pressure (between 15 to 30 psi) to heat and sterilize objects being treated. The effectiveness of this method of sterilization is a function of:

• Temperature
• Steam quality
• Time of exposure
• Pressure

When steam comes into contact with a surface of a cooler temperature, it condenses and releases a significant amount of latent heat energy. This energy quickly and effectively transfers to the microorganisms and irreversibly destroys the protein or enzyme within the cells.

Moist heat sterilization (steam) is considerably more efficient than dry heat due to the high thermal conductivity of steam and the ability of steam to penetrate porous materials better than dry air.

Why Pressure is Used in an Autoclave

Sterilization cannot be achieved solely by the use of pressure, however increasing the pressure will allow the water's boiling point to increase and therefore allow steam to achieve a higher temperature when compared with atmospheric pressure. For example:

• At atmospheric pressure, the boiling point is 100°C
• When steam pressure is increased therefore steam temperature may be as much as 121°C or higher.

Common sterilization conditions are:

• 121°C for 15-30 minutes,
• 134°C for shorter periods of time

Higher temperature allows for the more efficient destruction of microorganisms.

How Steam Achieves Sterilization

Sterilization occurs through the process of saturated steam transferring thermal energy into the load. To achieve sterilization, steam must:

• Enter the load
• Condense on loads that are cooler than the steam
• Release its latent heat
• Heat the load rapidly
• Result in the killing (destruction) of microorganisms

To achieve an effective sterilization of materials, steam must come into direct contact with each surface of the material to be sterilized. Therefore if a surface has air pockets or non-condensable gases on it this will prevent the steam from penetrating into that area - therefore reducing the total surface area of the material that is sterilized as a result.

Main Components of an Autoclave

While there may be differences in the design of an autoclave, the basic components of a pharmaceutical autoclave are similar.

1. Sterilizing Chamber

This is the main area that contains all the materials that will be sterilized. The chamber is typically made from stainless steel type 316L to protect against corrosion and hold up under pressure.

2. Steam Jacket

Many pharmaceutical autoclaves come with a steam jacket that encompasses the chamber. The jacket serves to:
- Keep the temperature of the chamber at a constant level.
- Prevent the chamber from experiencing build-up of condensation.
- Provide improved efficiency of the sterilization cycle.

3. Steam Supply System

The steam supply system provides steam to the sterilizing chamber of the autoclave. Good quality steam is required to sterilize properly, as the presence of non-condensable gases or excess moisture will negatively influence sterilization effectiveness.

4. Vacuum System

Vacuum systems use pumps to remove air before introducing the steam into the sterilizing chamber. It is important to remove all of the air from the chamber because trapped air will limit the penetration of steam.

5. Control System

Today’s autoclaves utilize a programmable logic controller (PLC) to provide automated operation for the autoclave. The control system provides:
- Control and Monitoring of Temperature
- Control and Monitoring of Pressure
- Control and Monitoring of Cycle Time
- Alarm System
- Recording Data

6. Drainage System

The drain system is used to remove the condensate produced during the sterilization cycle. Improper drainage may lead to cold areas within the sterilizing chamber, which would reduce the effectiveness of the sterilization process.

Working Cycle of an Autoclave

The cycle of an autoclave follows a strict pattern that is completed in order to provide reliable sterilization.

1. Loading Phase

Materials will be placed in the sterilization chamber per validated loading patterns. If the materials are loaded incorrectly, steam will not circulate properly and this will reduce the effectiveness of the sterilization process. Examples of improper loading are:
- Overloaded
- Too tightly packed
- Blocking drain holes

2. Air Removal Phase

The air must be removed from the sterilization area prior to starting the sterilization process. The two types of ways to remove the air are:
- Gravity displacement
- Vacuum assisted removal
Most pharmaceutical autoclaves use a pre-vacuum system because it gives the best steam penetration.

3. Steam Injection Phase

Once the air is removed from the sterilization area, saturated steam will enter the sterilization area and will replace the air and will preheat the load to the sterilization temperature.

4. Exposure (Holding) Phase

When the required sterilization temperature is achieved, the holding or exposure phase of sterilization starts. The critical parameters during this phase are:
- Chamber temperature
- Table time
- Stability of the pressure
Microorganisms are destroyed during this part of the cycle.

5. Exhaust Phase

At the end of the sterilization portion of the cycle, the steam will be exhausted from the sterilization chamber. The pressure will be reduced in a slow manner to protect the load.

6. Drying Phase

If necessary, the loads which were sterilized will have any remaining moisture removed by the vacuum drying process. Adequate drying is critical for porous loads and garments.

Types of Autoclaves Used in Pharmaceuticals

There are several different types of autoclaves that are used depending on the requirements of the process.

1. Gravity Displacement Autoclave

A gravity displacement autoclave utilizes steam to replace air inside the autoclave by causing air to move to the bottom of the chamber and thus be displaced downward. This type of autoclave is less complex but not as effective with more complicated loads.

2. Vacuum Autoclave

Vacuum assisted autoclaves are able to efficiently remove air prior to the introduction of steam. Vacuum assisted autoclaves are the predominant method used for sterilization in pharmaceutical sterile facilities.

3. Steam-Air Mixture Autoclave

A steam-air mix autoclave is used for the terminal sterilization of sealed containers when an accurate determination of pressure is required.

4. Double Door Autoclave

A double door autoclave is commonly used for separating sterile and lower class or non-sterile areas. These types of autoclaves help maintain contamination control by keeping clean and dirty sections of the facility separate from each other.

Factors Impacting Autoclave Performance

Directly affecting sterilization success are numerous variables involved in various processes involved.

1. Steam Quality

Poor steam quality can cause:
- Wet Loads
- Incomplete sterilization
- Variability of Temperature

2. Air Removal Efficiency

Residual air inhibits the ability of steam to contact surfaces directly, which is a frequent cause of the failure of sterilization.

3. Load Configuration

If loads are not loaded correctly, there will be areas that block the circulation of steam (e.g., cold spots).

4. Temperature Distribution

A necessary condition for reliable and consistent sterilization will be that the temperature of the chamber must be equally distributed.

Biological Indicators in Autoclave Validation

Biological indicators verify if the process used for sterilizing objects was effective. Biological indicators commonly contain spores of Geobacillus stearothermophilus. Spores have a high resistance to being killed by moist heat used during sterilization. If the spores are killed, then effective conditions for sterilization have occurred.

Validation of Pharmaceutical Autoclaves

Before an autoclave can be routinely used, it needs to be qualified and validated. Typical validation activities of autoclaves include:

• Installation Qualification (IQ)
• Operational Qualification (OQ)
• Performance Qualification (PQ)

Heat distribution and heat penetration studies during validation are critical.

Common Operational Problems in Autoclaves

Many pharmaceutical facilities face multiple operational issues that may impact the autoclave's performance. Examples of Operational Problems Include:

1. Wet Loads

Wet loads are often caused by:
- Poor steam quality
- Insufficient drying
- Drain issues

Failed biological indicators due to:
- Incomplete air removal
- Lack of time for complete exposure
- Temperature variation

2. Vacuum Leaks

Vacuum leaks artificially increase the vacuum inside the autoclave and therefore reduce vacuum efficiency and will affect steam penetration.

3. Data Integrity and Automation

Most modern pharmaceutical autoclaves use automated recording systems to meet the requirements for data integrity. An electronic system will typically include:
- Audit trail
- Electronic signature
- Cycle data storage
- Alarm history
These automated recording systems will support compliance with regulatory requirements.

Regulatory Expectations for Autoclaves

The regulations from the pharmaceutical regulators state that pharmaceutical companies must use validated, controlled sterilization methods. The inspector will look at:

• Validation documentation
• Biological Indicator records
• Calibrated measurements per cycle
• Cycle logs
• Periodic maintenance records

Autoclave failures are major compliance issues for sterile manufacturers.

Best Practices for Reliable Autoclave Operation

Many pharmaceutical companies operating effective sterilization programs adhere to several operational best practices. These include:

• Recommended Practices
• Using qualified steam systems
• Conducting regular preventive maintenance
• Validating load patterns
• Continuously monitoring critical process parameters
• Thoroughly training operators
• Promptly investigating sterilization failures

These practices improve both the assurance of sterility and operation reliability for autoclaves.

The use of autoclaves in the sterilization of equipment, components and other manufacturing materials in sterile pharmaceutical production is important since they are capable of supplying an effective and dependable method for providing steam sterilization. The functioning of an autoclave is based on efficiently altering the latent heat from saturated steam to microorganisms; thus, they provide rapid death to microorganisms.

For those in the pharmaceutical business, understanding the operation of an autoclave is much more than a theoretical process. The capability to provide effective and dependable sterilization through steam depends on having a good quality of steam, effective removal of air, the use of validated load patterns and continuous monitoring of critical process parameters. When operating in a highly regulated environment of sterile pharmaceutical manufacturing, it is critical to maintain validated and working autoclave systems in order to ensure the sterility of product, meet appropriate regulatory requirements and promote the safety of patients.

Frequently Asked Questions (FAQs) in Principle and Working of Autoclave

Q1. What is the principle of an autoclave?

Answer: Autoclaves operate along the principles of sterilizing by using steam and water vapor together.

Q2. Why is pressure used in an autoclave?

Answer: Using pressure to sterilize means you can raise the boiling point of water to 100°C and steam will be able to reach temperatures we need for sterilizing from boiling.

Q3. What is the common sterilization temperature in autoclaves?

Answer: The standard sterilization temperature in autoclaves is 121°C for pharmaceuticals using steam.

Q4. Why is air removal important in autoclaves?

Answer: Residual air in the sterilizing load can impede movement of the steam necessary for sterilization; therefore, removal of air is critical.

Q5. What are biological indicators used for?

Answer: Biological indicators contain chlorine-resistant spores that provide a definitive measure of the effectiveness of the sterilization cycle.

Q6. What causes wet loads after sterilization?

Answer: A wet sterile load after sterilization may be caused by one or more of the following reasons: steam quality, insufficient drying time or low vacuum pressure within the equipment.

Q7. Why is autoclave validation important?

Answer: Autoclave validation is important because it ensures consistent performance from the sterilization cycle as well; therefore, verification and compliance with regulatory agencies is established.

Q8. What do regulators review during autoclave inspections?

Answer: During inspections conducted by Regulatory Authorities, the following will typically be reviewed: records of validations, data for cycles being established, results from biological indicators and currently maintained/scheduled equipment maintenance records.