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Drug Delivery II > Sterilisation Methods > Flashcards

Sterilisation Methods Flashcards

1
Q

Define sterilisation

A

A process intended to kill (or) remove all types of micro-organisms with an acceptably low probability of one organism surviving.

  • One in a million chance of one non-sterile item
  • Sterility assurance level (ASL) of 10^(-6)
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2
Q

Broadly, list 4 methods of sterilisation

A

Heat
Irradiation
Chemical
Physical

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3
Q

What are the 3 things that heat inactivation depends on?

A

1) Heat
- heating temperature

2) Organisms
- microbial population
- heat-resistance of organisms

3) Time
- sufficient heating and holding time to destroy all organisms

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4
Q

Efficient of heat inactivation (or) thermal death rate increases with what 4 things?

A

1) increasing temperature
2) increasing heating time
3) decreasing initial population
4) decreasing heat resistance of micro-organism

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5
Q

Define thermal death kinetics

A

At constant temperature, the same percentage of microbial population will be destroyed in each unit of time at the rate proportional to the number of surviving organisms.

E.g. If a heat sterilisation process kills 90% of micro-organism population per minute, then for an initial population of 1000:

  • 90% of 1000 will be killed in 1st min
  • 90% of 100 will be killed in 2nd min
  • 90% of 10 will be killed in 3rd min
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6
Q

Write the equation that involves the thermal death rate constant at temperature T

A

k(T) = 1/t log(10)[N(0)/N(t)]

N(t) = number of organisms surviving at time t
N(0) = initial number of micro-organisms
k = rate constant
t = time of heating (min)
T = temperature

Higher k(T) = fast rate of kill

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7
Q

What is Decimal Reduction Time (D)?

A

Heating time (in minutes) required for 10 fold reduction (or) 1 log cycle of surviving organisms.

D value defines the rate of thermal inactivation at a specific temperature

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8
Q

What is the relationship between D and k(T)

A

D(temp) = 1/k(T)

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9
Q

What does the Z value define?

A

Heat sensitivity or resistance of micro-organism.
e.g. Larger Z values = heat resistant organisms.

It’s defined by increase in temperature requried to bring about ten-fold decrease in decimal reduction time (D value)
e.g. If D(121) = 2mins to D(124) = 0.2mins
therefore Z value = 124-121 = 3 degrees

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10
Q

What does the F(0) value define?

A

It defines LETHALITY in terms of the equivalent heating time in minutes at 121 degrees Celsius, using reference organism with a Z value of 10 degrees Celsius.

E.g. if temp 115degrees was maintained for 1 min. And the calculated F(0) value = 0.251 min. It’s the equivalent of heating at 121 degrees for 0.251 min.

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11
Q

How is F(0) calculated for a steam steriliser?

A

Use the sum of the AUC of heating time, holding time and cooling time:

F(0) = Σ Δt x 10^[(T-121)/Z]

note: Z value is normally 10

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12
Q

What is Sterility Assurance Level (SAL)?

A

It defines the DEGREE OF STERILITY in the treated batch of product.

E.g. SAL of 10^-6 = probability of 1 unsterile item in 10^6 items treated (i.e. 1 in a million chance of an organism surviving)

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13
Q

What type of heat is involved in Moist Heat Sterilisation? And how does this heat work?

A

Saturated Steam in an Autoclave.

At high temperatures, it holds a load of latent heat which is available for transfer without a drop in temperature when it condenses onto a cooler surface.
Heat transfer from steam to object occurs until object reaches temperature of the steam.
At this point is when protein coagulation and denaturation occurs.

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14
Q

Briefly list the steps in autoclaving (5)

A

1) Removal of air
2) Heat to temperature under high steam pressure
3) Hold temperature for required time
4) Cool
5) Depressurise

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15
Q

What is moist heat sterilisation used for?

A

Sterilisation of:
- dressings, surgical and diagnostic equipment, containers and closures.

  • terminal sterilisation of aqueous injections, opthalmic preparations, irrigation & haemodialysis

NOT for:
- non-aqueous preparations (anything that can ruined by water)

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16
Q

What are 3 instrumental indicators used to monitor steam sterilisation?

A

1) Thermometers
2) Pressure gauges
3) Thermocouples (temp sensitive tips connected to temp recorder outside steriliser - monitors only cold spots or temp fluctuations)

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17
Q

What are 3 types of indicators used to monitor steam sterilisation?

A

1) Instrumental indicators
2) Chemical indicators
3) Biological indicators (e.g. B. stearothermophilus - extremely heat resistant organism; D(121) = 2 min)

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18
Q

List some requirements of biological indicators in moist heat sterilisation (6)

A
  • Strain should not be stable
  • Non-pathogenic
  • Resistant to method used
  • Reproducible recovery
  • Not less than 10^5 viable spores/unit
  • Number should match the IF of the process
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19
Q

List some advantages and disadvantages of heat sterilisation

A

ADVANTAGE:

  • Lower temperature (121 degrees)
  • Shorter exposure time (15 mins at 121 degrees)
  • Aqueous thermostable preparations (e.g. aqueous injections, parenteral products, eye drops, O/W emulsions)
  • Sealed in heat stable plastic containers

DISADVANTAGE:

  • Heat labile preparations
  • Corrosive
  • Containers must be penetrable by steam
  • Difficult to monitor
  • Damp load (water inside)
  • Bursting of rigid containers
20
Q

What is Dry Heat Sterilisation?

A
  • Heat transferred by convection or radiation
  • Causes oxidative destruction of bacterial cell wall and cytoplasmic components
  • Higher pressure and longer holding time
  • Suitable to sterilise non-aqueous materials and metal equipment (due to non-corrosion)
21
Q

List 5 Hot Air Oven characterisitics

A

1) Electric heater to heat the oven (before loading)
2) Fan circulation (for uniform heat distribution)
3) Thermostat to maintain temperature
4) Heat lining of the chamber (insulation for protection)
5) Efficiency Indicator organism for HAO (B. subtilis; D(160 = 5-10 mins)

22
Q

What are some advantages and disadvantages of dry heat sterilisation?

A

ADVANTAGES:

  • Non-aqueous systems
  • Non-corrosive
  • Penetration
  • Dry process
  • Oily thermostable products

DISADVANTAGES:

  • Slow heating
  • Longer holding times (1-2 hrs)
  • High temperatures (160-170 degrees)
  • Not for aqueous preparations
23
Q

How does radiation kill micro-organisms?

A

Energy photons can induce excitation or ionisation of atoms in the living cells, depending on the level of energy and the penetration power (i.e. radiation dose)

  • Chemical reactions in the nucleic acid
  • Cell mutation
  • Cell death
24
Q

What defines Radiation dose and what does it depend on (3)

A 
It's the amount of energy (joules) absorbed per kilogram of material which gets irradiated.
It depends on:
- power of the source of energy output
- time of exposure
- density of the material treated
25
Q

Compare UV to Gamma irridiation

A
  • UV has lower energy & lower penetrating electromagnetic power
  • UV is more for surface penetration
  • UV is non-iodising radiation, whereas Gamma is.
  • UV causes excitation in atoms that alter DNA structure to cause mutation and cell death, whereas Gamma ionises vital cell components (DNA & cellular water) to cause cell death (production of free radicals reacting with DNA
26
Q

What are some disadvantages of UV light

A
  • Hazard (operator irradiated)
  • Poor penetration
  • Shielding, relflection
27
Q

List 4 factors affecting radiation sterilisation

A

1) Radiation dose (amount of energy absorbed per kg of material
2) Oxygen (oxidation)
3) Temperature
4) Organic substances (protective effect)

28
Q

What are some advantages and disadvantages of radiation sterilisation

A

ADVANTAGE:

  • Materials are not wetted or heated
  • Operated at ambient temp
  • Packed and sealed container in packaging
  • Continuous and automated

DISADVANTAGE:

  • Hazardous
  • Chemical changes in drug
  • Container deterioration
  • Small volume, low density
  • Expensive
  • Plant
29
Q

What is the mechanism of chemical sterilisation?

A
  • Alkylating agents
  • Addition of hydrocarbon groups to reactive groups of protein molecules
  • Site of action: Cell DNA during replication
30
Q

List 3 chemicals used in chemical sterilisation

A

1) Ethylene Oxide
2) Formaldehyde
3) Glutaldehyde

31
Q

What are 3 factors what affect Ethylene Oxide Sterilisation?

A

1) CONCENTRATION
- 400-700mg/L
- Allowance for absorption by packaging material

2) TEMPERATURE
- Increase effect at lower temperatures
- Increase in temperature will decrease exposure time

3) MOISTURE
- Moisture dissolves gas to form concentrated solution for the effect (optimal 33%RH)

32
Q

What are some ways to monitor Ethylene Oxide Sterilisation? (5)

A

1) Thermocouples
2) Humidity sensors
3) Weight of the EtO released from the gas cartridge for concentration estimation
4) Chemical indicators
5) Biological indicators (e.g. B. subtilis van niger)

33
Q

What are some limitations to Ethylene Oxide? (4)

A
  • Toxicity
  • Difficulty in Monitoring
  • Removal of residuals
  • Time consuming
34
Q

What are some applications of Ethylene Oxide? (4)

A
  • Dressings
  • Containers
  • Medical equipment
  • Implants
35
Q

How does Formaldehyde and Glutaldehyde sterilisation work?

A

Alkylating reaction with protein, DNA & RNA of organisms.

  • Formaldehyde fumigation
  • Glutaldehyde solution for soaking & rinsing of heat sensitive instruments
36
Q

What are some limitations of Aldehydes for chemical sterilisation? (5)

A
  • Poor penetration
  • Absorption by wrapping material
  • Inactivation
  • Toxicity (skin irritation)
  • Difficult to monitor
37
Q

List 5 uses of filters in physical sterilisation

A

1) Sterilisation of air and gases (in LFC & cleanroom)
2) Sterilisation of liquids
3) Sterilisation of solids/semi-solids
4) Quality Control tests
5) Purification of Water

38
Q

What are some desired properties of filters?

A
  • Inert, non-pyrogenic
  • Efficiently remove particles
  • Good flow rate
  • Resistant to clogging
  • Sterilisable
  • Reusable
  • Do not retain drug and other ingredients
  • Do not release filter components
39
Q

What is the mechanism of Depth Filters?

A

Compacted pads of fibres with pores and channels that depends on Sieving, Adsorption (VDW) and Retention (trapping) to filter out particles.
It’s state of arrest depends on the size, charge and velocity of particles.

40
Q

Explain the importance of Pore Size vs. Porosity in Depth Filters

A

Pore size is the diameter of the pore. The larger the pore size, the faster the flow will be, but it won’t trap smaller particles.
Porosity is the number of pores on a filter paper. The lower the porosity, the slower the flow, but the higher chance of trapping particles.

41
Q

What are some limitations of Depth Filters?

A
  • Uniform pressure is important
  • Retain liquid, loss of solvent
  • May not be suitable for sterilisation (chemical, heat) or reuse
  • Loss of formulation ingredients
  • Slow speed of filtration
  • Filter fibres may shed into the filtrate
  • The Filter can crack
42
Q

What are some advantages and disadvantages of Membrane Filters

A

ADVANTAGE:

  • High porosity
  • Fast flow and speed of filtration
  • Low fluid retention
  • Minimal solute adsorption
  • No shedding of filter components

DISADVANTAGE:

  • Narrow pore size range (only 0.22, 0.45, 0.8-0.12 micron filters)
  • Poor dirt handling capacity
  • Rapidly clogging
  • Limited easy of handling (can break easy)
43
Q

What are two Quality Assurance checks for monitoring filters

A

1) Integrity testing of membrane filters (Bubble point test)

2) Bacterial retention test (Microbial challenge test)

44
Q

Briefly explain how the Bubble Point pressure test works

A

1) Pressure of a test gas (N2) required to push out the liquid in a wet membrane filter.
2) At that pressure, gas bubble appear in the liquid. Once bubbles form after all liquid is being pushed out completely, you stop and read the pressure gauge.
3) Match the pressure reading the manufacture’s recommended bubble pressure for that particular pore size to determine its integrity.

The gas pressure is a measure of the pore diameter.
Smaller pore diameter requires higher pressure to push the liquid out.

45
Q

Briefly explain the Microbial Challenge test in filtering

A

1) Bacteria (Br. diminuta = 0.3 micron diameter) is slowly filtered (0.22micron) from a bacterial suspension.
2) Entire filtrate is cultured in broth medium (or) passed through another filter which is then cultured.
3) Filter passes test if no growth after 72 hours at 30 degrees Celsius

Drug Delivery II (6 decks)

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