Case Study: Decontamination and Validation
of Isolators Using Chlorine Dioxide Gas
Use of isolators improved throughput but the sterilization process had to meet
requirements as well.
ClorDiSys Abiopharma company looking to expand its production capabilities needed a way to improve its quality while increasing its throughput. Previously, production batches were processed within cleanrooms which would then
be decontaminated between each batch. It was found that a
move from cleanrooms to processing isolators could offer the
increase in production the company was looking for as long as
the sterilization cycle time could be kept short enough. In this
case, the company wanted a cycle time of less than two hours.
Chlorine dioxide gas was explored to see if either could fulfill
their requirements of achieving a 6-log sporicidal kill in less
than two hours. Due to the nature of the product, this had to
be accomplished in the presence of a potentially heavy biological load. Testing found chlorine dioxide gas able to meet the
requirements, and the company switched to processing batches
within isolators. The next step was validating the chlorine dioxide decontamination process.
Cycle development and validation
Cycle development for the chlorine dioxide gas decontamination cycles was performed by placing biological indicators (BIs)
throughout the isolator. Biological indicators consisting of over
one million geobacillus stearothermophilus spores impregnated
on paper and wrapped in Tyvek were used. Cycle development
started with the suggested cycle of 65% relative humidity, held
for 30 minutes of condition time, followed by a chlorine dioxide
gas concentration of 5 mg/L held for 30 minutes. Gas concentration is accurately monitored and precisely controlled utilizing
an integrated UV-VIS spectrophotometer. This ensures that
each cycle is repeatable by completing a cycle only when all process parameters are met. Some of the processing isolators had
different configurations and layouts, but the suggested cycle was
used for all isolators at the onset of cycle development. Both the
processing isolator and the packaging isolator have two glove
ports and are approximately 100 cubic feet in volume.
The initial cycle proved to be effective; however, multiple
cycles were tested and the final cycle chosen to be written
into their procedure was 65% relative humidity, held for 10
minutes of condition time, followed by a chlorine dioxide gas
concentration of 5 mg/L held for 50 minutes. It was decided
to shift some cycle time from the condition step over to the
exposure step as a conservative measure to increase the contact
time of the gas. This chosen cycle provided an 85 minute over-
all cycle time, inclusive of aeration where the gas is removed
from the isolator. The same cycle was used in all of their iso-
lators, as the configuration did not affect the efficacy of the
Validation of the decontamination cycle then took place by
verifying efficacy of three consecutive cycles in each isolator.
The isolators consisted of a main chamber, an airlock, and
a fill location. Approximately 40 biological indicators were
placed in the production isolator. For the packaging isolator,
25 BIs were placed in the packaging main chamber, 13 in the
airlock, and 21 in the mix/fill section in order to test the efficacy of the cycle throughout the isolator. They were placed in
various horizontal and vertical planes as well as in the hard
to reach sections of the manufacturing tools that are located
inside the isolator.
As part of the PQ, three decontamination cycles were
performed in the over the course of one day. Once the cycles
were complete, the biological indicators were dropped into
growth media under aseptic conditions and incubated for
seven days. BI controls were used as well, with non-exposed
biological indicators being dropped into growth media as a
means of ensuring that the biological indicators were viable.
This was then duplicated until three validation cycles had been
performed in each isolator. Upon completion of the incubation period, all BIs exposed to chlorine dioxide gas during the
validation cycles were found to exhibit no growth within the
media, providing validation of the chosen decontamination
cycle. Control indicators were found to exhibit biological
growth within the media after a period of 24 hours.
The biopharma company has been producing product and sterilizing the isolators for over one year. Both the switching of the
production process to isolators as well as the actual sterilization
of the isolators has been successful. Sterilization times are what
they were planned. The process was so successful that additional
isolators are in the works.
Kevin Lorcheim received his B.S. in Mechanical Engineering
from Rutgers University. He has been with ClorDiSys Solutions
Inc. of Lebanon, N.J. since 2006 as an engineer, helping to design
and launch new products and solutions for contamination control. www.clordisys.com