Moist Heat Terminal Sterilization for Controlled Release Materials

James AgallocoAgalloco & Associates

Presentation OverviewTerminal Sterilization Fundamentals

Steam Radiation

Current Best PracticesTS 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 DevelopmentsThinking outside the current box that might be a part of our future.

Terminal SterilizationRelies on a lethal treatment to microorganismsSaferPreferred by regulatory bodiesMethod of choiceDegradation of materials always a concernEasily reproducible processRelatively easy to validateNot for all materialsAssumed more expensive

Aseptic ProcessingRelies on removal / separation of microorganismsMore riskyClosely scrutinized by regulatorsMore widely usedMaterial quality / stability largely unaffectedMore variable processMuch harder to controlNo material issuesPresumed less expensive

Why TS is preferable to AP

Assembly

Component 1 Component 2 Formulation Component 1 Component 2 Formulation

Assembly

Sterilize

Sterilize Sterilize Sterilize

No post sterilization handlingExtensive handling is usually necessary

Why is there a preference?Patient safety concernsRecalls 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 GuidanceFDA – 2004 - Aseptic Processing GuidanceEMEA – 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?

Can the product be sterilised by:

no

no

no

Use pre-sterilised individualcomponents and aseptic compounding and filling

Use a combination ofaseptic filtration andaseptic processing

yesMoist heat at 121°C for 15 minutes

Moist heat with F0 = 8 minutes achieving SAL of 10-6 yes

Can the formulation be filtered through a microbial retentive filter

yes

EMEA Decision Tree

Sterilization / SterilisationThe America’s

PNSU of 10-6

LVP’s - 1971-72Part 212 Regulation 1976PDA TM#1 – 1978 & 2007Microbiology Based Validation PracticeFDA Sterilization Guidance – 1994Cycle parameters vary substantiallyAdapt cycle to product / load requirements

Europe121°C / 15 minutesHospital Problems -1972HTM-10 - 1980Engineering Based Validation PracticeHTM-2010 - 1993, EN 285 & EN 554, Eur. Ph., CPMP Decision Tree – 1998Strong preference for standard cycleAdapt product / process to standard cycle

Some Basic PerspectivesSome 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 PerspectivesSterilizing 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 MethodsOverkill Method–

For items that can tolerate substantial heat or radiation. Can be used for some very stable products.

Bioburden / Biological Indicator MethodBalance of lethality and stability concerns.Common option for moist heat TS processes.

Bioburden MethodLowest possible adverse effectBasis for most radiation sterilization validation.

Terminal Sterilization ConcernsTerminal sterilization processes require consideration of the effects of maximum treatment conditions for their potential deleterious effect on the materials being processed.

SterileStable

SterileNon-Stable

Non-SterileStable H

eat

or R

adia

tion

In

put

Validation Methods Compared

Demonstrated PNSU

Expected Shelf Life

Information NeededFor Validation

Heat / Radiation Input to Materials

BioburdenMethod

Bioburden / BIMethod

OverkillMethod

Products & Containers - SteamSolutions, 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 TargetThe 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

106

103

100

10-3

10-6

10-9

10-15

10-12

10-18

3 6 12 15 18 21 24 27 309

Biological IndicatorDeath Curve

BioburdenDeath Curve

Popu

latio

n

Time

F0 = 8.0 minutes F0 = 8.0 minutes

D121 of BI = 0.5 minutes D121 of bioburden = 0.005 minutes

N0 of BI = 106 N0 of bioburden = 100 ( or 102)

PNSU for BI = 10-10 PNSU for Bioburden = 10-

1,598

0loglog NDFNu +

−=

Where,Nu = Probability of Non-sterile Unit (PNSU also known as SAL)D= natural resistance of bioburdenF= Fvalue or lethality of processNo= bioburden count per container

Bioindicator Bioburden

TS Processes / Practices on the Horizon

How not to test TS productsC

onta

min

atio

n R

ate

N/A Cleanroom

TS SterilityTesting

N/A

EMTesting

How to test TS productsC

onta

min

atio

n R

ate

N/A Isolator

TS SterilityTesting

N/A

EMTesting

Contemporary TS Processesusing Moist Heat

Terminal / Non-Porous LoadsAir 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 CyclesThe common autoclave cycles can be used, as well as some others.

Gravity Displacement Single Pre-Vacuum Multiple Pre-vacuum Steam-AirSteam-Water-Air (Raining Water)Immersion Continuous Sterilizer

Gravity Displacement CycleSteam Inlet

Steam Trap

Tem

pera

ture

Time

Heat-up Exposure Cool-down

Multiple Pre-vacuum Cycle

Pre-vac Com e-up Exposure Exhaust D rying Atm osphericBreak

Pressure

Tem perature

Courtesy of Fedegari Autoclavi, SPA

Steam-Air Sterilizer

Steam-Air-Water Sterilizer

Courtesy of Fedegari Autoclavi, SPA

Advanced Steam Designs

Continuous Sterilizer

Internal Pressures During Cycles

Heating CoolingSteady State

T = 80°CP = 1.8 Bar

T = 122°CP = 3.7 Bar

T = 100°CP = 2.4 Bar

T = 100°CP = 2 Bar

T = 122°CP = 3.1 Bar

T = 80°CP = 1.5 Bar

Air Overpressure Cycle

Sterilization Cycle DevelopmentScreen 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 StudiesContainer mapping

Probe position in containerLoad mapping

Position of load in chamberBoth hot and cold spot determination

Load sizes & patternsMinimum, maximum loadsUse of dummy load components (fixed loads)

Container Sizes / Fill VolumesMinimum and maximum container sizes Multiple fill volumes in single container

Container Mapping - Vertical

Container Mapping - Horizontal

Key Validation ConcernsMinimum / 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 LoadsMaximum 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 ChoicesGeobacillus stearothermophilus (rarely) ATCC 7953 or 12980 Clostridium sporogenes ATCC 51232Bacillus coagulansBacillus subtilis ATCC 5230Bioburden 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 productConsider use of SCDM for microbiological challenge units to simplify testing.

Use of D & z ValuesD-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 importanceTheir measurement by manufacturers and users is non-routine. 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, quantityKind, type, species, genus, origin?Seasonal variationPositive & Negative controls on methodsKinds of products

growth supportivehighly contaminated

Filtration method as adapted from sterility testUSP microbial methods adaptedNeed for periodic monitoringEstablishment of action / alert levels

Container-Closure IntegrityIt 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 InterfaceAll 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

VIAL VIAL

Inoculum

1 2

3

4

Stopper Stopper

Some TS ExperienceMinimum F0 requirements ranging from 2 to 38 minutesGlass / plastic containers – 0.5 to 500 mLBI’s used – G. stearothermophilus, B. subtilis 5230, B. atrophaeusProduct D121 values – 0.2 – 6 minutesContainers – vials, ampules, syringesAseptic & non-aseptic fills

Parametric ReleaseFrom 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 BoxPost-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 SuggestionDr. 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 pre-sterilization 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 Processing10-3 - Percentage of Contaminated Units (not an SAL)Implied Estimate of Sterility Assurance

Terminal Sterilization10-6 - Probability of a Non-sterile Unit (PNSU)Quantitative Assessment of Sterility AssuranceAssumes 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 APComponent 1 Component 2 Formulation

Assemble Sterilize

Sterilize Sterilize SterilizeThis process could be either moist heat or radiation

Post Aseptic Fill Heat Treatment

Conventional TS Post-aseptic fill Treatment

SterileNon-Stable

Non-SterileStable

SterileNon-Stable

SterileStable

Sterile Stable

Heat In

put

A New Perspective Decision Tree

Can the product be sterilized bymoist heat, achieving a minimum PNSU of 10-6?

Sterilize by moist heat to minimum PNSU of 10-6

Can the formulation be sterilized by filtration?

Use pre-sterilized product, components, aseptic compounding and filling

Sterile filter, aseptically process and fill

Yes

Can the product be sterilized bymoist heat, achieving a PNSU of 10-3-10-6?

Sterilize by moist heat, to a PNSU of 10-3-10-6

No

No

YesCan the product be sterilized bymoist heat, using 121 C for 15 minutes?

No

Sterilize by moist heat, using standard cycle

Yes

Yes

No

Is the product stable at 100 C

Yes

Is the product stable at 80 CNo

Validate destruction using B. megaterium –D100 = ~1 minute

YesValidate destruction using >>106 of non-sporeformer

No

Yes

Possible Post A/P Heat TreatmentsReduced F0 and/or time-temperature

- F0 of 2,4,6, or 8 - No standards exist

Processing at less than 121°C100°C for X minutes – lethal for most spores and all non-spore formers80°C for X minutes – lethal for some spores and all non-spore formers60°C for X minutes - lethal for nearly all non-spore formers

ISO 15883 – The A0 ConceptThis 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.

tAT

Δ=∑−10

)80(

10

What these changes might meanMovement 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 ProcessesIf 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.

ConclusionIn 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