Moist Heat Terminal Sterilization for Controlled Release Materials
James Agalloco Agalloco & Associates
Presentation Overview Terminal Sterilization Fundamentals
Steam Radiation
Current Best Practices
TS processes and approaches that everyone, including regulators can agree on. Current processes with a modest twist. Those may that create will likely create some angst.
Expected Future Developments
Thinking outside the current box that might be a part of our future.
Terminal Sterilization Relies on a lethal treatment to microorganisms Safer Preferred by regulatory bodies Method of choice Degradation of materials always a concern Easily reproducible process Relatively easy to validate Not for all materials Assumed more expensive
Aseptic Processing Relies on removal / separation of microorganisms More risky Closely scrutinized by regulators More widely used Material quality / stability largely unaffected More variable process Much harder to control No material issues Presumed less expensive
Why TS is preferable to AP Component 1 Component 2
Formulation
Assembly
Component 1 Component 2
Sterilize
Sterilize
Formulation
Sterilize
Assembly Sterilize
No post sterilization handling
Extensive handling is usually necessary
Why is there a preference? Patient safety concerns Recalls for lack of sterility are predominantly associated with aseptically processed materials. Terminal processes are destructive of microorganisms in the container and fewer variables can impact the process. Aseptic processing requires careful control of many more variables and is therefore more prone to contamination.
Which process to choose? Regulators require firms to evaluate TS processes before accepting an aseptic processing solution.
FDA – 1994 - Sterile Product Submission Guidance FDA – 2004 - Aseptic Processing Guidance EMEA – 1999 – Decision Trees for the Selection of Sterilization – CPMP/QWP/054/98
But are these guidance documents sufficiently clear and flexible to be of real value?
EMEA Decision Tree Can the product be sterilised by: yes
Moist heat at 121°C for 15 minutes no Moist heat with F0 = 8 minutes achieving SAL of 10-6 no Can the formulation be filtered through a microbial retentive filter
yes
no Use pre-sterilised individual components and aseptic compounding and filling
Use a combination of aseptic filtration and aseptic processing
yes
Sterilization / Sterilisation
The America’s PNSU of 10-6 LVP’s - 1971-72 Part 212 Regulation 1976 PDA TM#1 – 1978 & 2007 Microbiology Based Validation Practice FDA Sterilization Guidance – 1994 Cycle parameters vary substantially Adapt cycle to product / load requirements
Europe 121°C / 15 minutes Hospital Problems -1972 HTM-10 - 1980 Engineering Based Validation Practice HTM-2010 - 1993, EN 285 & EN 554, Eur. Ph., CPMP Decision Tree – 1998 Strong preference for standard cycle Adapt product / process to standard cycle
Some Basic Perspectives Some products should always be TS
WFI, saline, LVP’s (D5W, Ringer’s, etc.)
Some products are incompatible w/ TS (at least by steam) and should be aseptically filled.
Freeze-dried, dry powder, water free products, etc.
The focus of the effort should be on those which fall between these extremes. Controlled release products are a greater concern because of their unique product delivery concerns.
Terminal Sterilization
A balance must be achieved between the need to maintain a safe, stable and efficacious product while providing sufficient heat input to attain a minimum level of sterility assurance.
Material Perspectives Sterilizing processes should be a compromise between the degradation effect on the materials and destruction of microorganisms. A sterilization process that destroys all microorganisms, but renders the item being sterilized unfit for use is of no value. The sterilization process and the specific product formulation and container must be suited to each other. There are few universal answers, and some of those that appear to be broadly applicable may be wrong.
Sterilization Validation Methods Overkill Method–
For items that can tolerate substantial heat or radiation. Can be used for some very stable products.
Bioburden / Biological Indicator Method
Balance of lethality and stability concerns. Common option for moist heat TS processes.
Bioburden Method
Lowest possible adverse effect Basis for most radiation sterilization validation.
Terminal sterilization processes require consideration of the effects of maximum treatment conditions for their potential deleterious effect on the materials being processed.
Sterile Non-Stable Sterile Stable Non-Sterile Stable
Heat or Radiation Input
Terminal Sterilization Concerns
Validation Methods Compared Demonstrated PNSU
Expected Shelf Life Information Needed For Validation Heat / Radiation Input to Materials Bioburden Method
Bioburden / BI Method
Overkill Method
Products & Containers - Steam Solutions, suspensions, and emulsions can all be terminally steam sterilized. A minimum water content of approximately 5% is considered necessary, but this must be evaluated. Glass and plastic pre-formed vials, BFS, glass and plastic syringes have all been successfully processed. Interpolation of container sizes, formulation strength, etc. is possible.
Remember the Real Target The most common error associated with terminal sterilization (and perhaps sterilization in general) is forgetting that the intent is destruction of the bioburden to low levels (a Probability of a Non-Sterile Unit [PNSU] of not more than 1 in 106 units). What happens to the biological indicator (if there is one) is largely irrelevant outside of the context of the validation exercise.
BI & Bioburden Relative Resistance 10 6 10 3 10 0
Population
Biological Indicator Death Curve
10 -3 10 -6 10 -9
10 -12 10 -15
Bioburden Death Curve
10 -18
3
6
9
12
Time
15
18
21
24
27
30
Bioindicator
Bioburden
F0 = 8.0 minutes
F0 = 8.0 minutes
D121 of BI = 0.5 minutes
D121 of bioburden = 0.005 minutes N0 of bioburden = 100 ( or 102) PNSU for Bioburden = 10-
N0 of BI = 106 PNSU for BI = 10-10
1,598
−F logNu = + logN0 D Where, Nu = Probability of Non-sterile Unit (PNSU also known as SAL) D= natural resistance of bioburden F= Fvalue or lethality of process No= bioburden count per container
TS Processes / Practices on the Horizon
How not to test TS products Cleanroom
TS
Sterility Testing
N/A
Contamination Rate
N/A
EM Testing
How to test TS products Isolator
N/A
TS
Sterility Testing
EM Testing
Contamination Rate
N/A
Contemporary TS Processes using Moist Heat
Terminal / Non-Porous Loads Air over-pressure of the load may be required to maintain container integrity. Steam quality testing is irrelevant. Materials sensitive to excess heat can be processed. Minimum and maximum time-temperature or F0 requirements are needed. Container-closure interface sterilization can be a concern if components aren’t sterile.
Terminal Sterilization Cycles The common autoclave cycles can be used, as well as some others.
Gravity Displacement Single Pre-Vacuum Multiple Pre-vacuum Steam-Air Steam-Water-Air (Raining Water) Immersion Continuous Sterilizer
Steam Inlet
Temperature
Gravity Displacement Cycle Heat-up
Exposure
Time
Steam Trap
Cool-down
Multiple Pre-vacuum Cycle
P re-vac
C om e-up
P ressure Tem perature
E xposure
Exhaust
D rying
A tm ospheric B reak
Steam-Air Sterilizer
Courtesy of Fedegari Autoclavi, SPA
Steam-Air-Water Sterilizer
Courtesy of Fedegari Autoclavi, SPA
Advanced Steam Designs
Continuous Sterilizer
Internal Pressures During Cycles T = 100°C P = 2 Bar
T = 122°C P = 3.1 Bar
T = 80°C P = 1.8 Bar
T = 122°C P = 3.7 Bar
Heating
Steady State
T = 80°C P = 1.5 Bar
T = 100°C P = 2.4 Bar
Cooling
Air Overpressure Cycle
Sterilization Cycle Development Screen formulation for terminal sterilization. Selection the correct equipment / process. Determining the slowest / fastest to location in filled product containers. Determining the slowest / fastest to heat zone of load. Define how much lethality is enough based upon bioburden. Define load sizes and patterns. Product stability evaluation.
Mapping Studies Container mapping
Probe position in container
Load mapping
Position of load in chamber Both hot and cold spot determination
Load sizes & patterns
Minimum, maximum loads Use of dummy load components (fixed loads)
Container Sizes / Fill Volumes
Minimum and maximum container sizes Multiple fill volumes in single container
Container Mapping - Vertical
Container Mapping - Horizontal
Key Validation Concerns Minimum / maximum F0 criteria are required. Tight temperature range at steady state is preferred. Hot and cold spot determination in load (may be a region rather than a single point). Temperature & BI challenge performed together. Need to define routine probe locations. Cold spots are rarely monitored in commercial processes Correlation developed between control location and cold / hot spot to regulate process. Bioburden monitoring instituted as routine measure if not an aseptic fill.
Maximum and Minimum Loads Maximum loads are typically all that will fit in a chamber in a normal loading pattern. Minimum loads are arbitrary minimums which a firm might process. Some of the minimums used are a single tray, or single box. The utility of maximum and minimum loads depends to a large extent on the range of lot sizes produced. There are firms which have chosen to validate only maximum loads, and any load smaller than maximum is made up to maximum with dummy units. More widespread is the validation of maximum and minimum loads, which affords greater flexibility in batch size.
Bottles of Convenience Monitoring of sterilizer cold spot is not required for process control. Correlation between the cold (and hot spot) with the monitored location should be established during cycle development / validation. A fixed monitoring location can be used provided its process requirements are defined to assure conditions at the points of interest are know in relation to the monitored location.
Biological Indicator Choices Geobacillus stearothermophilus (rarely) ATCC 7953 or 12980
Clostridium sporogenes ATCC 51232 Bacillus coagulans Bacillus subtilis ATCC 5230 Bioburden organisms
Must know D-value in product or product substitute
Test Fluids (Product Surrogates) Water for Injection, normal saline, salt solutions, SCDM, other microbiological medias and buffers, match product viscosity & solids content? Advantages – Reduce the amount of product required for validation purposes, Widely used for preliminary mapping studies, etc. If a growth medium is used, may simplify microbial challenge studies. Disadvantages - If used for microbiological challenges, additional D-values must be obtained. Must be shown to resemble product. Selection Criteria - Cost, safety, resemblance to product, ease of testing, use as physical and/or biological model for product Consider use of SCDM for microbiological challenge units to simplify testing.
Use of D & z Values D-values - of critical importance
Never use a biological indicator without knowledge of the D-value on the substrate or in the product. Supplier data is normally from a paper strip . Requires internal resources - Biological Indicator Evaluation Retort {BIER} vessel, detailed microbiological methods
z-values - of less importance
Their measurement by manufacturers and users is nonroutine. In most cases the values given in the literature are utilized without difficulty. Varies only slightly over the temperature range of most interest.
Bioburden Information #, amount, quantity Kind, type, species, genus, origin? Seasonal variation Positive & Negative controls on methods Kinds of products
growth supportive highly contaminated
Filtration method as adapted from sterility test USP microbial methods adapted Need for periodic monitoring Establishment of action / alert levels
Container-Closure Integrity It is important to ensure that the initial and long term microbial barrier properties of the container-closure system are not compromised by the sterilization cycle. Initial development and validation of a sterilization cycle should include an assessment of the package integrity, when sterilized at the maximum exposure time and temperature.
Closure-Container Interface All LVP manufacturers (and some others) inoculate the seal area of the stopper / glass with B. atrophaeus to confirm lethality where steam might not easily penetrate. A 1x106 CFU challenge might be excessive at this location, given the minimal potential for bioburden. If both container and stopper are sterilized prior to filling, this evaluation isn’t necessary.
Stopper Vial Interface Inoculation Stopper
VIAL
Stopper 1 2 VIAL
3
4
Inoculum
Some TS Experience Minimum F0 requirements ranging from 2 to 38 minutes Glass / plastic containers – 0.5 to 500 mL BI’s used – G. stearothermophilus, B. subtilis 5230, B. atrophaeus Product D121 values – 0.2 – 6 minutes Containers – vials, ampules, syringes Aseptic & non-aseptic fills
Parametric Release From a risk and science perspective there is no value in performing a sterility test on terminally sterilized products. The only thing that a sterility test could potentially detect would be a failure to run the cycle, and depending upon the product characteristics even this detection is not assured. There is the impression that a “laboratory” test is required, however thermal or dosimetry data is more likely to indicate process failure than a lab test. The real obstacles with respect to parametric release are regulatory and compendial, not scientific.
Breaking out of the Box Post-aseptic filling lethal treatments at temperatures that kill spores have been used for decades. While this is not in the strictest sense terminal sterilization it is a means by which microbial risk can be mitigated. Many pathogenic organisms are killed very efficiently at temperatures in the 70-80oC range or at lower radiation doses. We shouldn’t think of aseptic processing or terminal sterilization as an either/or proposition. Post-aseptic filling treatments should be more broadly applied.
Dr. Sasaki’s Suggestion Dr. Sasaki suggested at the USP Open Conf. in 2002 that parametric release could be considered for processes that deliver as little as Fo=2 minutes. To those convinced that only overkill processes are suitable for use in moist heat sterilization this idea may seem preposterous. Environmental endospores do not have a D121 higher than 0.2 minutes, vegetative cells would have D121 values in some cases >100,000X less. So, a process yielding a F0 of 2 minutes would provide a ten log spore reduction against the most resistant presterilization bioburden. With that in mind Dr. Sasaki’s suggestion doesn’t seem preposterous at all, in fact it seems downright logical.
Aseptic Processing & Terminal Sterilization Aseptic Processing
10-3 - Percentage of Contaminated Units (not an SAL) Implied Estimate of Sterility Assurance
Terminal Sterilization
10-6 - Probability of a Non-sterile Unit (PNSU) Quantitative Assessment of Sterility Assurance Assumes known F0, D and bioburden N0
Terms cannot be added to determine an overall SAL for a combined process.
What if? Is there a benefit to a terminal treatments (moist heat or radiation) following aseptic processing? Absolutely, but we have been fixated on processes that kill highly resistant spores. Almost everyone agrees that this type of process would risk to the patient. Almost no one agrees on what type of post aseptic fill lethal process should be used.
TS and AP Component 1 Component 2
Sterilize
Sterilize
Assemble
Formulation
Sterilize
This process could be either moist heat or radiation
Sterilize
Post Aseptic Fill Heat Treatment Sterile Non-Stable Sterile Stable Non-Sterile Stable Heat Input
Sterile Non-Stable
Sterile Stable Conventional TS
Post-aseptic fill Treatment
A New Perspective Decision Tree Can the product be sterilized by moist heat, using 121 C for 15 minutes?
Yes
Sterilize by moist heat, using standard cycle
Yes
Sterilize by moist heat to minimum PNSU of 10-6
No Can the product be sterilized by moist heat, achieving a minimum PNSU of 10-6?
No Can the product be sterilized by moist heat, achieving a PNSU of 10-3-10-6?
No Can the formulation be sterilized by filtration?
Yes Is the product stable at 100 C
No Is the product stable at 80 C
No
No Yes Yes Yes
Yes
Sterilize by moist heat, to a PNSU of 10-3-10-6
Use pre-sterilized product, components, aseptic compounding and filling Validate destruction using B. megaterium – D100 = ~1 minute Validate destruction using >>106 of nonsporeformer Sterile filter, aseptically process and fill
Possible Post A/P Heat Treatments Reduced F0 and/or time-temperature
- F0 of 2,4,6, or 8 - No standards exist
Processing at less than 121°C
100°C for X minutes – lethal for most spores and all non-spore formers 80°C for X minutes – lethal for some spores and all non-spore formers 60°C for X minutes - lethal for nearly all nonspore formers
ISO 15883 – The A0 Concept This standard developed for hospital disinfection equipment evaluates thermal processes in the 80 C range in a manner identical to F0 with the time expressed in seconds due to the susceptibility of vegetative cells to destruction by moist heat. Minimally acceptable A to disinfect (destroy vegetative cells) are 600 seconds for medical devices in contact with intact skin and 3000 seconds for critical medical devices. The use of this system may be well suited for post-aseptic fill heat treatments. ( T −80 ) 10
A = ∑10
Δt
What these changes might mean Movement away from the “black” or “white view of “aseptic processing or terminal sterilization” Approaches that visit the “gray” area in between the extremes are desirable. If not “aseptic processing & terminal sterilization”, then perhaps “aseptic processing and supplementary lethal treatment”. The end result is less risk to the patient, improved stability over classical TS processing and substantially fewer issues in aseptic processing control.
Future Processes If we recognize that the concern is risk to the patient, then post-aseptic fill processes make perfect sense. We shouldn’t thing in terms of current PNSU or even F0 targets, but in slightly different terms. The A0 model or something like it makes sense below 121 C for moist heat.
Conclusion In the future we can make our products safer, we just have to be willing to re-think some of our traditional goals for patient safety. With more and more biological products coming to market, new thinking is necessary to provide greater assurance than our current practices allow.
PostScript
Walter Kelly, 1971
