Sterile Filling: Processes, Requirements, and Technological Implementation
Last updated: 02. March 2026
Sterile filling is a pharmaceutical-technical manufacturing process in which liquid or semi-solid products are filled into sterile primary containers under strictly controlled conditions and immediately hermetically sealed. While conventional processes use pre-sterilized containers, in Blow-Fill-Seal (BFS) technology, containers are formed directly from the plastic melt during the process, meaning the inner surface of the container is created under sterile conditions from the start. The goal is to permanently ensure the microbiological purity of the final product and to exclude contamination during the filling and sealing process. Processes like these are primarily used when subsequent terminal sterilization is not possible or would impair the quality of the product.
Cleanroom Conditions and Process Control
Manufacturing takes place in qualified cleanrooms with defined air purity classes and is subject to regulatory requirements such as the EU GMP guidelines (particularly Annex 1). These are published by the European Commission in the EU GMP Guide. The European Medicines Agency (EMA) coordinates the European network of authorities; the national competent authorities (NCAs) of the member states are responsible for inspections and monitoring compliance. For global market access, especially to the USA, compliance with the FDA's CGMP regulations (21 CFR 210/211) is also crucial.
In addition to the environment, all components in contact with the product undergo validated sterilization. This includes:
- Containers (created process-integrated in BFS)
- Closures
- Lines
- Machine parts
Additionally, barrier or isolator technologies (such as RTP systems) minimize the influence of personnel and ambient air entry. To ensure process stability, validated cleaning and sterilization processes (CIP/SIP), continuous particle and microbial monitoring, and comprehensive in-process controls are used.
Process Steps
Typical process steps of a corresponding system are:
- Preparation and sterilization of the product, primary packaging materials, and product-contacting equipment parts.
- Provision of the product in closed, sterile transfer systems.
- Filling under cleanroom conditions (Grade A).
- Immediate, hermetic sealing of the containers.
- Optional terminal sterilization of the sealed final containers (e.g., in an autoclave for PP containers).
- Integrity tests (e.g., 100% CCI testing) and quality assurance controls (e.g., AOI).
In BFS technology, the steps of forming, filling, and sealing are integrated into a single, closed system operation. Whether step 5 is performed depends on the thermal stability of the formulation. Many modern active ingredients, such as biopharmaceuticals, are temperature-sensitive; for these, a special "cool-BFS" process is often used to minimize thermal stress during forming.
Differentiation from Aseptic Filling
Although the terms are often used synonymously, there is a clear definition: "Sterile" describes the state of being free from germs (absence of viable microorganisms), while "aseptic" refers to the sum of measures and procedures used to maintain this state during manufacturing and filling. Aseptic processes such as BFS primarily aim at the prevention of contamination to guarantee the sterility of the product without the need for quality-reducing terminal sterilization.
Technological Implementation: The Blow-Fill-Seal (BFS) Method
An established technology is the BFS process, in which plastic granulate is extruded, formed into a container, filled, and hermetically sealed. A technological provider of these systems is Rommelag with its bottelpack systems. By eliminating external handling steps, the risk of contamination is significantly reduced. The process is suitable for single-dose units (SVP) as well as large-volume applications (LVP).
Application Areas
Typical fields of application are:
- Pharmaceuticals: e.g., injection and infusion solutions, ophthalmics (such as eye drops), biologics, vaccines, and inhalation solutions.
- Diagnostics: Reagents, buffer solutions, test media.
- Cosmetics: Sterile creams, lotions, or serums without preservatives.
- Veterinary medicine: Parenteral preparations.
Advantages and Technical Features
Sterile filling using BFS technology offers significant advantages over conventional processes in terms of process reliability and cost-effectiveness. By fully integrating container forming, filling, and sealing into one system, critical interfaces are eliminated.
The key advantages at a glance:
- Minimized contamination risks: Since the containers are formed directly from the hot plastic melt and filled in a closed system, external transport and cleaning steps for primary packaging materials are eliminated.
- Reduced operator intervention: The high degree of automation minimizes the influence of the human factor – one of the primary sources of contamination in aseptic manufacturing.
- High process stability: Validatable CIP/SIP cycles and a controlled CCS (Contamination Control Strategy) ensure reproducible results at the highest quality level.
- Flexibility and efficiency: The process enables the economical production of single-dose formats without preservatives, which is essential especially for modern biopharmaceuticals.
Due to these properties, sterile filling at Rommelag is not just a manufacturing process, but a