1. A. Sterilization Ibrahim A. Alsarra, Ph.D. King Saud University
College of Pharmacy
Department of Pharmaceutics
PHT 351: Sterile Dosage Forms
Summer Semester of H
A. Sterilization
Ibrahim A. Alsarra, Ph.D.

2. PHT 351: Sterile Dosage Forms
Outlines
Principles of Sterilization: Introduction
Methods of Sterilization: An introduction
Sterilization Criteria
Sterilization Validation and Monitoring
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PHT 351: Sterile Dosage Forms

3. I. Principles of Sterilization
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4. PHT 351: Sterile Dosage Forms
Introduction
Definitions and Terminologies
Sterility:
The total absence of viable microorganisms and it is an absolute state
Sterilization:
The inactivation or elimination of all viable microorganisms and their spores, based on a probability function. The sterilization process is usually the final stage in the preparation of the product.
Aseptic Processing:
Those operations performed between the sterilization of an object or preparation and the final sealing of its package. These operations are carried out in the complete absence of microorganisms.
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5. PHT 351: Sterile Dosage Forms
Introduction …(cont.)
Disinfection:
A process which aims to reduce the number of harmful (pathogenic) microorganisms in a particular situation. It is not an absolute process i.e. will eradicate infective vegetative organisms but not spores.
Antiseptics:
Chemical substances applied to living tissues in humans or animals in order to arrest or prevent the growth of microorganisms by inhibiting their activity without necessarily destroying them.
Bactericide:
Any agent that destroys microorganisms
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6. PHT 351: Sterile Dosage Forms
Introduction …(cont.)
Bacteriostat:
Any agent that arrests or retards the growth of microorganisms.
Germicide:
Any agent that destroys microorganisms, but not necessarily bacterial spores.
Sterility Assurance Level (SAL):
A term related to the probability of finding a nonsterile unit
following a sterilization step. It usually is expressed in terms
of the negative power of 10 (i.e. 1 in 1 million = 10-6).
Bioburden:
The number of viable microorganisms in or on an object or population entering a sterilization step (usually expressed in
colony forming units per unit time).
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7. PHT 351: Sterile Dosage Forms
Introduction …(cont.)
The aim of sterilization process:
Is to destroy or eliminate microorganisms that are present on or in
an object or preparation, to make sure that this has been achieved
with an extremely high level of probability and to ensure that the
object or preparation is free from infection hazards.
The currently accepted performance target for
a sterilization process:
Is that it provide a probability of finding a nonsterile unit of less
than 1 in 1 million. That is, the process (including production,
storage, and shipment) will provide a Sterility Assurance Level
(SAL) equal to or less than 10-6.
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8. Contamination: General Facts
Some microbes (bacteria, molds, etc) multiply in the refrigerator,
others at temperatures as high as 60o.
Microbes vary in their oxygen requirements from strict anaerobes
that cannot tolerates oxygen to aerobes that demand it.
Slightly alkaline growth media will support the multiplication of
many organisms while others flourish in acidic environments.
Some microorganisms have the ability to use nitrogen and carbon
dioxide from the air and thus can actually multiply in distilled
water.
In general, however, most pathogenic bacteria have
rather selective cultural requirements, with optimum temperatures
of 30 to 37 and a pH of 7.0
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9. II. Methods of Sterilization
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10. PHT 351: Sterile Dosage Forms
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11. III. Sterilization Criteria
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12. 1. Death Rate or Survival Rate
Each sterilization method can be evaluated using experimentally derived values (death and survival rates) representing the general inactivating rates of the process.
Plotting the logarithm of surviving organisms against time of exposure to the sterilization method. In most instances, these data show a linear relationship, typical first order kinetics, and suggest that a constant proportion of contaminant population is inactivated in any given time interval. Based on such inactivation curves, it is possible to drive values that represent the general inactivation rates of the process. For example, based on such data, it has become common to drive a decimal reduction time or D value, which represents the time under a stated set of sterilization exposure conditions required to reduce a surviving microbial population by a factor of 90%.
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13. 1. Death Rate or Survival Rate… (cont.)
Death value (D): is the time required to reduce the population by 90% at specified temperature. D value can be obtained from the death curve (i.e. the straight line relationship between the log viable count of a bacterial population and time when the population is exposed to a lethal temperature.
The graph shows three hypothetical population of the same organism exposed to the same killing agent (e.g. heat). Notice that the populations A, B, and C die at the same rate (all three lines are parallel) although population C dies sooner than B and B dies sooner than A because of the initial sizes (ml of microorganism) are smaller.
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14. 1. Death Rate or Survival Rate…(cont.)
New Finding
It is sometimes known as Thermal death time was found that complete killing of microorganisms is approached by applications of 6 D values. By extending the process to include 6 D values, most of the remaining population is inactivated, reducing the population of one organism surviving to one in 1 million.
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15. 2. D Value and Inactivation Factor (IF)
From the D value for a particular combination of organism/time/temperature an “inactivation factor” (IF) can be calculated, e.g. if the D value of an organism exposed to a temperature of 121 °C for 15 minutes was 2 minutes:
The IF would be 1015/2= 107.5
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16. 3. Death Rate Constant (K)
Microbiologist in various industries employee a value known as the death
constant (k) to compare susceptibilities of different microorganism to a
given control agent. The more rapidly a population can be sterilized, the
longer the death rate constant.
The death rate constant is the same and independent of the initial
population size. It would only be different if were are comparing different
organisms. The death rate constant can be calculated using the following
formula:
Where:
T= Time in minutes of exposure to a killing agent
N0= Initial number of microorganisms
Nt = Final number of microorganisms after treatment
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17. 3. Death Rate Constant (K)…(cont.)
Example
IF at time 0, the size of population is 10,000,000 and after 3 minutes the population is reduced to 10,000; the K value is found to be 1.00 for curve A. Calculate K value for curve B and C?
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18. 4. Z Value or Thermal Destruction Value
Z value relates the heat resistance of a microorganism to changes in temperature. The Z value is the number of degrees in temperature change required to produce a 10-fold change in D value. Bacterial spores have a Z value in the range °C while most non sporing organisms have Z values of 4-6 °C.
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19. 4. Z Value or Thermal Destruction Value … (cont.)
Example:
If the D value for Bacillus stearothermophilus spores at 110 °C is 20 minutes and they have a Z value of 9 C, this means that at 119 °C the D value would be 2.0 minutes and at 128 °C the value Z value would be 0.20 minutes.
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20. 5. Q Value or Temperature Coefficient
Q value also gives a measure of the relative heat resistance of different microorganisms and describes the change in the death rate over a 10 °C change in temperature. It does the same, like Z value, but is less commonly used.
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21. PHT 351: Sterile Dosage Forms
6. F Values
F value is a measure of the deadliness or lethality of the total
process of sterilization and equates heat treatment at any
particular temperature with the time in minutes at a designated
reference temperature that would be required to produce the
same lethality in an organism of stated Z value. The death rate
constant can be calculated using the following formula:
Where:
Tc= Load temperature at time dt
Z= 10 °C
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22. VI. Sterilization Validation and Monitoring
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23. Indicators for Validation …(cont.)
A. Biological Indicators
It involves incorporating a viable culture of a stated species of microorganisms. The biological indicators are usually used to check or monitor the efficacy of a sterilization cycle.
The efficacy of a biological indicator depends on:
1- Sensitivity
2- The viability of the organisms
3- The storage conditions before use and after the
incubation
4- The conditions of the culture after sterilization
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PHT 351: Sterile Dosage Forms

24. Indicators for Validation …(cont.)
A. Biological Indicators …(cont.)
Organism
Sterilization Process
Bacillus subtilis
Dry heat
Bacillus stearothermophilus
Steam
Clostridium sporogenes
Ethylene oxide
Bacillus pumulis
Ionizing radiation
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25. Indicators for Validation …(cont.)
B. Chemical Indicators
They are used to indicate whether a particular batch of product has been through a sterilization process; they are not used to indicate whether a specific process of sterilization was suitable or successful.
Disadvantage:
They undergo some physical and chemical changes when exposed to the conditions of the sterilization process.
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26. Indicators for Validation …(cont.)
B. Chemical Indicators … (cont.)
Indicator
Main uses and specific feature
Browne’s tubes
Color change at specified temperature for appropriate length of time. Good for all sterilization processes. They are not used as quantitative purposes.
Heat sensitive tape
Used to steam sterilization. Tape that is heat sensitive, which changes color after contact with steam
Chemical
degradation test
Check the degradation kinetic of a compound by U.V. spectrophotometry. It is a useful technique for moist heat sterilization
Indicator for
ethylene oxide
Change in color upon exposure to a given time and concentration of ethylene oxide
Chemical dosimeters
Monitor quantity of the radiation dose in radiation sterilization.
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