PDA Letter Article

Microbial Control During Low-Risk Aseptic Processing

PDA staff author David Jaworski, MBA, PDA, Inc.

This is the fourth and last of a series of articles on microbial contamination of pharmaceuticals.

In the two months following the publication of the article on high-risk aseptic processing, there were four additional recalls of sterile drug products due to potential microbial contamination and lack of assurance of sterility.

Looking at current practices that are utilized in the manufacture of sterile injectable drug products, there are three general risk classes based on the presence of personnel in proximity to open containers and routes of exposure to contamination sources. Each of these risk classes is associated with specific aseptic processing manufacturing operations currently in use. The high-risk and medium-risk aseptic processing classifications have been previously discussed in this series of articles, and low-risk aseptic processing will be the focus of this article.

Drug and biologics manufacturers should carefully evaluate the risk class that applies to their aseptic manufacturing process. Additional information on contamination sources and contaminants is discussed in Table 1 below.

Environmental monitoring still must be used as a tool to evaluate processing and operational task suitability, and to evaluate the cleanliness levels achieved in cleanroom and work environments used during aseptic processing. An effective environmental monitoring system is a prerequisite that must be established before aseptic operations commence. Even with low-risk aseptic operations, microbial risks must be evaluated routinely to ensure there was no breach of asepsis in the barrier systems employed. The frequency of sampling can be reduced as a company gains confidence in the barrier systems utilized, but the company assumes the risks associated with a sterility failure that is not detected due to a reduction of sampling frequency. Additional information on environmental monitoring can be found in PDA’s Technical Reports No. 13 (Revised 2022) Fundamentals of an Environmental Monitoring Program and Technical Report No. 13-2: Fundamentals of an Environmental Monitoring Program Annex 1: Environmental Monitoring of Facilities Manufacturing Low Bioburden Products (2020).

All aseptic drug manufacturers should consider using low-risk aseptic processing to ensure that patients, who are usually in poor health, receive the highest level of protection against infection when they receive ophthalmic or injectable drug products. The diligent application of low-risk aseptic processing could reduce patient adverse events, recall, and drug shortages. Moreover, although it may have higher initial costs due to design, low-risk aseptic processing could reduce the cost of manufacturing due to lower facility, labor, and cleaning costs.

The following analysis identifies significant issues and provides the best practices to be utilized for the low-risk class in aseptic processing. As a prerequisite, a firm must understand and follow all regulatory guidance applicable to their own aseptic filling operations. This article does not address terminally sterilized drug products.

Low-Risk Aseptic Processing

Low-risk aseptic processing refers to automated/robotic operations with physical barriers between personnel and first air and where manual manipulations are only allowed during set-up and preventive maintenance. These advanced manufacturing systems are uniquely designed to remove personnel from most aspects of sterile drug product preparation, sterilization/depyrogenation, and filling processes. The most advanced systems incorporate bulk drug preparation, sterile filtration, component preparation, filling, sealing, visual inspection, and labeling/packaging operations into a continuously isolated and mechanized system. Standardized material transport containers (cassettes) are used for raw materials, active drug substances, excipients, solvents, stoppers/plungers, primary containers, seals, and cleaning/sterilizing agents. These types of containers allow for rapid access ports to make the process a closed system with an extremely low chance of microbial contamination.

These types of filling systems can be designed to be very compact or can be complex and long. In either case, the ISO 5 filling zones are minimal due to the engineering design, and many of these filling systems rely upon ready-to-use components. Automated or robotic systems can be used to control the filling processes and allow either lights-out operation (a production method that is running on its own, even in a dark or empty factory) or continuous processing of the drug products. In many cases, these filling lines are dedicated to one drug product and can run for extended periods before cleaning, retooling, and sterilization are needed.

Proper Design of the Cleanrooms and ISO 5 Equipment

ISO 5 filling zones are integrated into the filling systems and will not have personnel interventions. In some cases, robots or manually operated manipulators are used to move components, adjust equipment, or install equipment components. Sterile tools could be stored inside the cleanrooms and isolators.

Some of these filling systems have been designed to work without the need for a cleanroom, but it is advisable to utilize ISO 8 cleanrooms to contain the filling system as an extra layer of protection from contamination if a breach in the containment system occurs. As such, these surrounding cleanrooms can be small, with only enough space for equipment, material transfer, and personnel movement.

Quality assurance should lead the multi-disciplinary contamination control strategy team to develop robust design specifications and provide guidance to the engineers designing these systems. This oversight will minimize the chance of microbial contamination due to poor system design. Contamination control at material entry points, sanitary equipment design, unidirectional airflow, sample collection/testing, waste management, and use of sensors are all important considerations in an effective design. Due to the unique nature of automated/robotic systems, it is useful to set up a meeting with the U.S. FDA’s Emerging Technology Program to ensure the system design is robust and minimizes the risk of microbial contamination.

Personnel Flow

Depending on the design of the process, there may be no need for personnel except for maintenance and engineering staff to enter the cleanrooms. Remote video monitoring and advanced sensor technology can eliminate the need for equipment operators and quality observers in the cleanroom itself. Material handling at the entry and exit to these advanced filling systems are the only points where personnel may be present, but even these tasks can be automated.

Personnel Gowning

The use of sterile garments is minimal and only required during maintenance and cleaning of the cleanrooms and if the filing system is not cleaned and sterilized. In addition, there are automated systems available to clean and sterilize the cleanrooms that house the filling equipment. Otherwise, clean, low particle-shedding garments and sterile nitrile gloves are required during maintenance work. The focus for these operations is particle reduction to minimize the risk of microbial contamination during maintenance, hence increasing the bioburden beyond the capabilities of the qualified sterilization process.

Cleaning of Components

See the article on medium-risk aseptic processing if components are cleaned and sterilized in-house as part of the filling system or separately.

Firms must ensure their suppliers or engineers have designed effective cleaning processes and use standardized protective packaging. The need for dry heat sterilization of glassware should be minimized, and firms should work with the glass manufacturers to source ready-to-use glassware components. If the glassware manufacturer can supply pyrogen-free glassware after the glass stabilization step, it will minimize stress on the glassware during the filling process and reduce the incidence of glass particulates.

Design of Material Flow and Usage

The use of double-wrapped material component primary packaging is encouraged to minimize the risk of contamination during transportation. Evaluation of the cassette supply of components is encouraged during the engineering design of the filling system. This will minimize the chance of breakage, reduce potential contamination of the components during handling, and improve the ease of material handling tasks.

Design of Equipment

Proper engineering design focuses on rapid access port or cassette material transfers, sealed leak-proof containment, closed transfer systems, internal reactive automated control systems, and automated change-over processes, which are designed to prevent entry of personnel and their associated microbial contaminants into the ISO 5 workspaces. Effective air prefiltration, such as the use of dual high-efficiency particulate air (HEPA) and ultra-low particulate air (ULPA) filtration or ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers)-grade prefilters and ULPA filters should be used in all isolator systems. Isolators and filling equipment must be designed to have easily cleanable surfaces and fluid paths. Gaps, ports, and poorly designed seals (e.g., valve, motor, filter) could allow bacterial contamination; therefore, these components should be minimized or removed from the design. Tools needed for product change-over, adjustment, or maintenance should be maintained in the ISO 5 isolator and sterilized in place. Minimal tool use is needed in robust engineering designs.

Cleaning Issues

Periodic cleaning of the entire system may be needed based upon the engineering design and drug products being produced.


Understanding the microbial contamination risks associated with each type of aseptic processing currently used to manufacture drug products is important. This article series provides information for sterile drug manufacturers to consider when they design their aseptic process, and the information can also be used to improve their aseptic filling operations and reduce contamination risks. The best practices needed for each aseptic risk class should be incorporated into each firm's aseptic filling operations. Knowledge of the sources and types of contamination can be used to train personnel involved in aseptic process design, facility construction, equipment design, preparation of standard operating procedures, and operations. The need for effective and persistent training in how to reduce or eliminate microbial contamination is essential to the manufacturing of aseptic drug products.

Patients who receive aseptically filled drug products assume that the drugs are sterile and that their health will not be affected by microorganisms that could cause hard-to-treat infections and potentially lead to death. Aseptic drug manufacturers must ensure that this scenario does not happen.

The following resources should be used in conjunction with this article as a company evaluates their aseptic processes:

  • PDA Technical Report No. 54: Implementation of Quality Risk Management for Pharmaceutical and Biotechnology Manufacturing Operations
  • PDA Technical Report No. 69: Bioburden and Biofilm Management in Pharmaceutical Manufacturing Operations
  • PDA Technical Report No. 90: Contamination Control Strategy Development in Pharmaceutical Manufacturing
  • PDA Technical Report No. 34: Design and Validation of Isolator Systems for the Manufacturing and Testing of Health Care Products
  • PDA Points to Consider of the Aseptic Processing of Sterile Pharmaceutical Products in Isolators
  • EU GMP Annex 1: Manufacture of Sterile Medicinal Products

The following table summarizes the potential for contamination by sources and common types of contaminants for properly designed systems.

Table 1 Potential Sources of Contamination for Low-Risk Aseptic Processing 
Contamination sourcesLow-risk aseptic processing
PersonnelPersonnel are only present in ISO 5 workspaces during set-up and maintenance, followed by vaporized hydrogen peroxide or other sterilization processes. Minimal chance of introducing personnel-associated contaminants.
Components and suppliesAutomated cleaning and sterilization or depyrogenation of components reduces the potential for contamination of components and supplies. Some systems require ready-to-use components that have been qualified and validated for use.
LiquidsFluid pathways that are cleaned and sterilized in place have a minimal risk of contamination if the process is designed properly and validated. Failure to ensure turbulent flow and full wet coverage of all piping during cleaning can result in cross-contamination. Microbial contamination caused by filter failure is typically low if pharmaceutical sterilizing grade cartridge filters are used.
ToolsTools that are removed from the ISO 5 isolator and routinely used manually after disinfection can cause microbial contamination due to personnel contact and variable disinfection procedures.
EquipmentIntegrated equipment systems with design or construction and operating flaws increase the risk of equipment caused microbial contamination. The use of ineffective sterilization cycles for isolators and product contact surfaces can cause microbial contamination.
ProcessesPoorly designed integrated processes significantly increase the risk of microbial contamination. Only containment failure could lead to microbial contamination.

There is a low risk of a contamination source since the design relies upon isolators. Risk does increase when maintenance occurs within the isolator. Poorly designed cleanrooms or the lack of cleanrooms can increase the risk of microbial contamination.

If not detected and fixed, HEPA/ULPA filter or seal failures will allow airborne microorganisms to contaminate the drug products being filled.

Skin cells/hairNot present during normal operations. Particles are present in cleanrooms outside of isolators. Could be present during maintenance, worn equipment operation, or isolator breaches.
FibersNot present during normal operations. Could be present during maintenance or isolator breaches.
DustRemoval of dust relies upon air filtration processes or glove box to control and is not usually present in ISO 5 work zones. Could be present during maintenance or isolator breaches.

Not usually present.

Poor isolator and equipment design and preventative maintenance procedures can cause microbial contamination. The use of non-validated sterilization cycles for isolators and product contact surfaces can lead to microbial contamination.


Not usually present.

Poor isolator and equipment design and preventative maintenance procedures can cause microbial contamination. The use of non-validated sterilization cycles for Isolators and product contact surfaces can lead to microbial contamination.


Ineffective cleaning, disinfection, and filtration steps to remove viruses from biologics and ATMPs can allow viruses to proliferate in these products.

Drug products do not currently have limits on viruses and controls are not addressed.

LubricantsDepends upon source of lubricants and use of equipment. Seal failure could be the source of contamination.
MetalsHigh probability if equipment is not adjusted properly or maintained. Usually, contamination risk increases when poor engineering designs are used, and machine or process interventions occur.
Component particles

Particles are likely to be present for ready-to-use components if not controlled at the manufacturer’s facility. If component transfer systems rely upon automated transfer containers and equipment where outside surfaces of cassettes do not interact with components within the aseptic filling system, there is minimal chance of contamination from exterior container surface contaminants.

Contamination sources are dirt accumulated during shipping, packaging materials, and poorly cleaned components at supplier facilities or in-house.

Chemical residues (cleaning agents/previous drug products)

Manual cleaning processes can allow chemical residues to accumulate over time and should only be used after maintenance or a sterility breach has occurred.

The use of clean, in-place systems with appropriate solvent composition minimizes the risk of chemical residue accumulation.