Leak detection in plastic ampuls
The formation of the primary container is an integral part of the BFS operation and container-closure defects can be a major
problem. US regulatory authorities require that "as a final measure, the inspection of each unit of a batch should include
a reliable, sensitive, final product examination that is capable of identifying defective units (e.g. "leakers")"(8). It is
also stated in the EU guidelines that "containers closed by fusions, e.g., glass or plastic ampoules should be subject to
100% integrity testing"(5).
There are multiple leak-detection technologies available, such as the vacuum-decay method, high-voltage leak detector, or
near infrared leak detection. Among these methods, the vacuum-decay method is often selected for biological manufacturing
becauese it has no product quality impact (even though there is no documented product quality impact from other methods to
the authors' knowledge). During vacuum decay leak detection, the test article is placed inside a chamber, which is then evacuated
to a known pressure. If the product container exhibits a leak, the chamber pressure will rise at a rate greater than a predetermined
The qualification of a leak-detection machine can be achieved by challenging the system with calibrated needle valves, or
by means of "leaky" samples, created by either laser microdrilling or capillary tube insertion into ampuls. In the authors'
experience, creation of "leaky" samples of ampuls is not reproducible, and needle valve is a preferred method to qualify the
leak detection machine. Leaky samples created by laser microdrilling or capillary tube insertion in plastic materials have
many challenges. Most plastic resins, such as LDPE, do not have the required material characteristics (too soft and poor adhesion)
to support reliable mounting of a capillary or to maintain a consistent hole size. The drilling process with LDPE yields a
conical-shaped orifice that results in flow rates that are difficult to predict. Furthermore, the verification process is
destructive in that the flow rate is measured under vacuum, which can result in obstruction of the orifice by the product.
Therefore, the actual test sample used cannot be verified prior to testing. The variables of shipping, handling, and pressure
as a result of air transportation could also result in inconsistent results.
Alternatively, the needle valves can be calibrated with a flow meter to a specific flow rate corresponding to a specific orifice
size. Calibrated needle valves represent a suitable qualification approach to the system that will demonstrate the system's
ability to detect an actual leaking sample with a known hole size and flow rate.
Another main challenge with in-line leak detection operation is the high false rejection rate. Due to the high temperature
required for plastic extrusion, the ampuls, immediately after BFS process, are notably warmer than room temperature. When
the products are immediately placed in a vacuum-detection chamber, the heat from the ampul can cause a slight increase in
pressure which the instrument may interpret as a leaky sample, which will trigger a false rejection signal. Therefore, it
is highly advisable to have the product equilibrated to room temperature prior to subjecting the product to vacuum leak detection.
Packaging requirements, extractables and leachables
The primary containers of ampuls manufactured using BFS process are plastic materials, such as LDPE or PP, which are gas-permeable
to some degree. During long-term storage, water vapor may diffuse out of the ampul resulting in alterations in drug concentration.
Conversely, oxygen permeation could cause protein oxidation. Gas permeation can be minimized by sealing the plastic ampuls
inside laminated foil pouches (as a secondary packaging layer). For example, in the development of the Pulmozyme drug product,
studies showed that protein concentration increased by more than 30% due to water loss when the naked product was stored at
37 °C for ~700 days (1). Such water loss was prevented by adding an aluminum foil pouch as a secondary packaging layer. In
addition, the aluminum foil pouch protects the drug product from light-induced degradation. Furthermore, oxygen-sensitive
products can be sealed into pouches under a nitrogen blanket (overlay) to provide additional protection against oxidation.
Secondary packaging materials are typically comprised of multiple layers of polymers (i.e., polyester, PP, or polyethylene),
inks, adhesives, as well as possibly unreacted monomers and oligomers derived from adhesive materials. When in direct contact
with primary containers, these materials have the potential to penetrate through plastic ampuls. In addition, the direct contact
between the liquid product and the primary container (even though the primary container material is typically made of much
cleaner polymers) could lead to extraction of chemicals. These chemical extracts and leachates from plastic packaging materials
could act as adjuvants in stimulating an immune response in the patient (9). Leachates would especially be of concern if the
product is to be injected subcutaneously, as the localized concentration of product and adjuvant is more likely to stimulate
the production of neutralizing antibodies than intravenous injection or inhalation (9). Therefore, it is imperative that the
extractable and leachable program for plastic ampul products be conducted with both pouched and unpouched samples to understand
the respective extracts and leachates from both the primary and the secondary packaging materials (10–12).