Strategies for gamma sterilization of pharmaceuticals(2)
1. Sterilization
Strategies for
Gamma Sterilization of
Pharmaceuticals
by Ruth Garcia, Betty Howard, Rose LaRue, Glenn Parton, and John Walker
Steris Isomedix Services (Mentor, OH)
Sterility is desirable not only for medical devices, but also to ensure the safety of
parenterals or injectable drugs. Various methods of reducing microbial load
in drugs and parenterals are available.
crucial step in pharmaceu- • No residue like EtO leaves behind. include potency, efficacy, stability, bio-
A tical production is steril-
ization. There are many
sterilization methods to
choose from, such as
steam, sterile filtration, ethylene oxide
gas (EtO), electron beam (E-beam),
and gamma radiation. Each technique
•
•
•
More penetrating than E-beam.
Low-temperature process.
Simple validation process.
The first aspect to consider when
sterilizing with gamma is product tol-
erance to the radiation. During use of
compatibility, and chemical accept-
ability. Per guidelines under the
International Conference on Harmo-
nization (ICH), known as Technical
Requirements for Registration of
Pharmaceuticals for Human Use, it is
recommended to use high-performance
has aspects that make it suitable or this type of radiation, high-energy liquid chromatography (HPLC), mass
unsuitable for the sterilization of a photons bombard the product, caus- spectrometry, or gas chromatography
particular product. ing electron displacement within. to characterize and compare different
For example, EtO, while being a These reactions, in turn, generate analytical aspects of irradiated prod-
highly effective method, leaves behind free radicals, which aid in breaking uct versus nonirradiated product.
potentially hazardous residuals and can- chemical bonds. Disrupting microbial A qualified laboratory should per-
not reach products in airtight packages. DNA renders any organisms that sur- form package testing. It is often recom-
E-beam, while being one of the fastest vive the process nonviable or unable mended to have an aerosol challenge
methods of sterilization, cannot pene- to reproduce. performed on the product and pack-
trate well into dense product or bulk However, these high-energy reac- aging. This test entails placing the
packaging of some products. In addi- tions also have the potential to disrupt packaged product inside an aerosol
PHOTO COURTESY STERIS ISOMEDIX SERVICES (MENTOR, OH)
tion, the product complexities of hetero- bonds within the pharmaceutical for- chamber and exposing it to high levels
geneous components often require mulation, to weaken the strength of of bacterial spores. The product is
extensive product qualification. Gamma packaging materials, and to cause then subjected to a sterility test, which
radiation can cause certain product and changes in color or odor in some shows whether or not the packaging
package materials to degrade. materials. For these reasons, drug maintains a sufficient barrier.
manufacturers should perform pre- In addition, at least one physical
GAMMA BENEFITS qualification Dmax (maximum dose) challenge should be performed on the
Gamma radiation does have some testing, whereby the drug and its pack- packaging, if applicable. These in-
significant advantages over other aging are subjected to a high dose of clude the peel test to determine the
methods of producing sterile product. gamma radiation and then evaluated amount of pressure needed to open
These benefits include: for stability and functionality. the seal; the burst test to determine the
Usually, the manufacturer will be amount of pressure needed to burst
• Better assurance of product sterility the party responsible for drug testing. the package and to locate areas of
than filtration and aseptic processing. Parameters to characterize typically weakness in the package; and the dye
2. Sterilization
migration test, which deter mines Radiation Sterilization.”
whether dye travels through the seals Method 1 encompasses product
of the package. If a shelf-life claim is with bioburden up to 1 million colony-
desired, most labs will perform accel- forming units (CFUs). It allows for
erated aging. Typically, incubation at extremely low and high doses and is
55°C for 6.5 weeks equals one year on well known throughout the gamma
a shelf (this may vary depending on sterilization industry. The steps are
the drug formulation). These tests are simple and straightforward. First of
performed on aged products. all, 10 product samples from each of
Performing a fraction of or all of three separate production batches
these tests following a high dose of must have bioburden testing per-
gamma radiation will give the manu- Steris’ new JS 10,000 continuous and formed on them. This quantitative
facturer a good idea of product and incremental Cobalt-60 irradiator is ready to measure, or count, of the number of
packaging suitability for gamma radia- process customers’ products. organisms on the unsterilized product
tion. (A high dose is usually considered provides an excellent tool for deter-
to be in the 50–60-kGy range or high- ed drug products, are composed largely mining the minimum dose necessary
er, preferably twice the minimum.) of water. Water dissociates as a result for sterilization.
Many materials are highly resistant to of exposure to radiation and is a major Bioburden tests should be accompa-
radiation. If possible, the manufactur- source of free radicals. These free radi- nied by a determination of recovery
er should choose materials that are cals can cause chemical compromise, efficiency. This allows the laboratory
resistant to the effects of gamma prior so drugs with high water content often to calculate a more accurate biobur-
to the initial production phases. respond poorly to irradiation. den number. The average bioburden
Performing irradiation on product of each batch and the overall average
HANDLING DEGRADATION in a frozen state can mitigate these of all product units should be deter-
If a drug experiences degradation, effects. If the product can be safely mined. If any single-batch bioburden
discoloration, or any other physical frozen and thawed, the potential exists level is more than twice that of the
malady due to the high dose of 50–60 to irradiate it without, or with less, overall bioburden, that batch average
kGy, the manufacturer can begin test- product degradation. Freezing the should be used. Otherwise, the overall
ing at lower doses. One method drug traps free radicals in the ice crys- average should be used.
involves testing at particular intervals, tals, reducing their freedom to move Afterward, the verification or sub-
such as at 5 or 10 kGy. For example, a about. This may induce them to lethal dose must be set. Using
drug that fails at 50 kGy may be stable recombine with each other, rather AAMI/ANSI/ISO 11137 Table B.1,
at 40 kGy. then disrupt molecules in the product find the bioburden number equal to or
However, some drugs may continue itself. This would possibly improve just higher than that of the product.
to exhibit effects from the radiation at drug resistance to degradation during Follow the row to the column labeled
extremely low doses. Another test gamma irradiation. Other options SAL 10–2, where the verification dose
entails dropping the dose to half of such as freeze-drying and/or using will be found.
the original high dose. This would cut free-radical scavengers may also alle- The final phase includes testing for
the range of possible maximum doses viate the degradation effects seen in Bacteriostasis/Fungistasis (B/F) and
in half. If the product is stable at the some products. setting the verification dose. The B/F
new dose, then the max dose will fall test validates the sterility test by deter-
somewhere within the top half of the FINDING THE RIGHT DOSE mining whether the product formula-
original high dose. If the product is The next step is to set the minimum tion inhibits bacterial or fungal
still showing instability, the max dose sterilization dose, which will provide growth. If inhibition is seen, steps
must fall in the lower half of the origi- the desired sterility assurance level must be taken to neutralize it. The test
nal high dose tested. This method may (SAL). There exist two commonly is required only once in the lifetime
reduce the number of irradiations used, industry accepted, validation of a product, but it is recommended
necessary for establishing this infor- techniques, with several variations annually. Without such a test, sterility-
mation. All in all, the end product of for special circumstances. The first testing results are meaningless.
this testing should be a solid maximum technique for discussion, Method 1, To begin the verification dose exper-
tolerated dose for the particular drug is found in AAMI/ANSI/ISO iment, send 103 product units (100 for
product. 11137:1994, “Sterilization of Health sterility testing and 3 for B/F) to the
Many pharmaceutical products, Care Products: Requirements for sterilization provider for irradiation at
including parenterals and orally ingest- Validation and Routine Control— the verification dose ± 10%. If the
3. Sterilization
dose exceeds the prescribed verifica- Should positives occur, another dose- lation is not necessary.
tion dose by more than 10%, then the setting method must be used. The organism most commonly used
product must be sacrificed and new Also contained in AAMI 11137 is for radiation challenge is Bacillus
product irradiated. If the dose is lower an alternative validation procedure pumilis. It was once believed that this
than 90% of the prescribed dose, the referred to as Method 2. Method 2 organism was highly resistant to gam-
remainder of the testing may be per- provides for dose setting based on ma. However, many organisms natu-
formed and a failing test would allow the actual radiation resistance of rally occurring in medical products are
for a retest. microorganisms as they naturally more resistant to radiation than
The product should then be sent to occur on a product. Of the methods B. pumilis, rendering this a poor surro-
the laboratory for sterility testing and cited, it can provide the lowest possi- gate organism. If no alternative exists,
B/F testing. If two or fewer sterility ble minimum dose. It is not used as however, this method may be accept-
tests turn positive, the product has frequently as Method 1 or VDmax, able. A D10 value (D value) of an
passed the validation, and the next due to more sample requirements and organism, in this case, is the amount of
step is to find the sterilization dose. associated costs. radiation (quantity of kGy) necessary
Manufacturers should follow the same Method 2 uses incremental dose to reduce the bioburden level by 1 log.
row in Table B.1 from which the verifi- data to select a verification dose. An example of a published D value
cation dose was taken, to the column Groups of samples from three produc- for B. pumilis is 1.7 kGy. Some caution
marked SAL 10 –6. This is the mini- tion batches are irradiated in dose should be taken in using a published D
mum sterilization dose. The product increments up to the point where an value, as D values can vary depending
now qualifies to be irradiated at a SAL of 10 –2 can be determined. A on the technique used to determine
range from the minimum dose to the Method 2 validation starts with the them and/or the inoculation substrate.
maximum dose determined during the random selection of 280 samples Also, D values, or the resistance of an
high-dose materials testing. (Method 2A) or 260 samples (Method organism to gamma radiation, can
The second type of validation is 2B) from each of three production change over time, analogous to antibi-
commonly known as VDmax. Found in batches of product. Samples are then otic resistance in microorganisms.
AAMI TIR 27:2001, “Radiation Steril- designated in groups of 20 samples for However, if this is the method to be
ization, Substantiation of 25 kGy,” this each dose increment. Method 2A uses used, the following is an example of
method requires fewer products and nine increments in 2-kGy increments, the calculation for determining mini-
results in a minimum sterilization dose and 2B uses eight doses at 1-kGy incre- mum sterilization dose.
of 25 kGy. However, only products with ments. All samples are tested for sterili-
1000 CFU or less qualify. ty. After the results of sterility tests Inoculation with 10 6 (1,000,000
The first step of this process is iden- are known, a series of calculations organisms):
tical to that of Method 1. Bioburden described in AAMI 11137 (section
data from 10 products from each of B3.4.2) a verification dose (D*kGy) is SAL = 10–6
three separate production batches determined. 106 to 10–6 = 12 log reduction
should be collected. Using Table 2 of An additional 100 samples from the D value 1.7 kGy × 12 log reduction
the TIR, the bioburden number equal batch designated from the initial sterili- = 20.4 kGy
to or just greater than the product’s ty tests are irradiated at the verification 20.4 kGy = 10–6 SAL dose
average bioburden is found. The sub- dose and tested to confirm sterility. Fol-
lethal dose is found by following the lowing these sterility tests, a steriliza- The following calculation deter-
row to the column labeled “Verifica- tion dose is calculated using the mines the necessary verification dose
tion dose” (SAL 10–1). Send 13 product equation appropriate to the specific for 10 products to show the efficacy
units (10 for sterility testing and 3 for method chosen (2A or 2B). of the above 20.4-kGy sterilization
B/F) to the sterilizer for irradiation at In extreme circumstances in which dose:
the verification dose ± 10%. Once the all efforts to neutralize bacteriostatic
irradiation is complete, send the prod- agents have been exhausted and other Log bioburden – log (1/#samples)]
ucts to the laboratory for sterility test- sterilization methods are unsuitable, × d-value = verification dose
ing. If one or fewer sterility tests turn dose setting can be done with inocula- Log 1,000,000 – log (1/10)] × 1.7 =
positive, the product can be irradiated tion of the product. The practice of verification dose
at a minimum dose of 25 kGy. If two inoculation, commonly used in the [6 – (–1)] × 1.7 = verification dose
positive sterility tests occur, a retest past, is not currently recommended [6 + 1] × 1.7 = verification dose
should be performed on 10 additional unless it is impossible to collect natural 7 × 1.7 = verification dose
products. This time, no positives are bioburden data from the product. For- 11.9 kGy = verification dose
allowed for substantiation of 25 kGy. tunately, in most cases, product inocu-
