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DD2 PAC3252 > Sterilisation Methods > Flashcards

Sterilisation Methods Flashcards

1
Q

Sterilisation by HEAT

A
  • heat produces thermal energy that is lethal to m.o, damages cytoplasmic membrane, cellular enzymes, DNA, RNA
  • Moist heat (Protein Coagulation)
  • Dry heat (Oxidation)
  • Factors (HOT): sufficient quantity of heat i.e. temp, Organisms i.e. need to know population and their heat resistance, Time needs to be sufficient heat and holding time to destroy them
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2
Q

Thermal death kinetics

A

At constant temp, same percentage of m.o will be destroyed per unit of time at the rate proportional to the number of surviving organisms

Log10Nt=Log10No-kTt

LogNT VS t

KT = thermal death rate constant at temp T

T in minutes

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3
Q

Decimal Reduction Time (D)

A

Heating time required from 10 fold reduction (1 log cycle) in number of surviving organisms
D=1/Kt

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4
Q

How do we know whether organisms are heat sensitive or heat resistant?

A

Z value

  • defines heat sensitivity (small z) or resistance (large z) of m.o
  • defined by increase in temp required to bring a 10 fold decrease in decimal reduction time
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5
Q

Fo value

A
  • defines the lethality in terms of equivalent heating time in minutes at 121 deg using reference organism with a z value of 10 deg
  • takes into account the equivalent lethal effect go lower temp compared with 121 deg
    Fo = T x 10^( T-121 / z )
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6
Q

Sterility Assurance Level SAL

A
  • Defines the degree of sterility in the treated batch of product
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7
Q

MOIST HEAT STERILISATION

A
  • saturated steam at high temp holds load of latent heat which can transfer without drop in temperature when it condenses onto a cooler surface
  • protein coagulation and denaturation of m.o
    Autoclaving
  • moist heat sterilisation under high steam pressure in an autoclave oven
  • steps involve remove air, heat to temp under high steam pressure, hold temp for required time, cool and depressurise
    Used for sterilising: dressings, equipment, aq injections only
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8
Q

Monitoring steam sterilisation

A

Instrumental indicators: thermometers, pressure gauges, thermocouples
Chemical indicators: Browne’s tube red to green, Bowie-Dick tape (light-dark), Steam-Clox strip (purple-green)
Biological Indicator: Spore strips, B. stearothermophilus

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9
Q

Biological Indicators

A
  • strain stable
  • non- pathogenic
  • Resistant to method used
  • reproducible recovery
  • not less than 10^5 viable spores per unit
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10
Q

Advantages of Moist Heat

A

Lower temp
Shorter exposure time
Aqueous thermostable preparations ie aq inj
Sealed in heat stable plastic containers

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11
Q

Disadvantages of Moist Heat

A 
Heat labile prep
corrosive
containers must be penetrable by steam
difficult to monitor
damp load
bursting of rigid containers
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12
Q

DRY HEAT STERILISATION

A
  • Heat transfer by convection or radiation
  • Oxidative destruction of bacterial cell wall
  • higher pressure and longer holding time (no rubber, plastic packages)
  • suitable for metal instruments, glass ware, powders, oils
  • also used for depyrogenation of glassware
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13
Q

Hot air oven

A

Electric heater to heat the oven
Fan Circulation to distribute heat evenly, max variation in chamber <10 temp
Thermostat to maintain temp
Heat lining to prevent heat transfer from inside
Efficiency Indicator: B. Subtilis var niger

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14
Q

Advantages of Dry Heat

A 
Non-aq systems
Non-corrosive
Penetration
Dry process
Oily thermostable products i.e. oily inn
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15
Q

Disadvantages of dry heat

A

Slow heating
Longer holding times
Higher temp
Not for aq preparations

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16
Q

moist heat vs Dry heat

A

Condensation, protein coagulation MOA, 121 for 15 mins under high steam pressure 15psi, B. Stearothermophilus, D121 = 2 mins

Convection and radiation, oxidative destruction, 160-170 for 1-2 hours, B subtilise var niger, D160 = 5-10 mins

17
Q

Radiation

A
  • electromagnetic radiation: energy in motion in the form of non-particulate electromagnetic rays
  • Energy photons can induce excitation of atoms in living cells depending on level of energy and penetrating power
  • chemical reactions in nucleic acid, cell mutation and death
  • UV, GAMMA
18
Q

UV Radiation

A

Electromagnetic radiation of lower energy and poor penetrating power

  • non-ionising, can cause excitation of atoms to higher energy state
  • cause chemical reactions in nucleic acid, alter DNA, mutate, cell death

Uses:
Air - lower m.o counts in clean rooms by UV lamps fitted ducted air supply systems
Water - UV water steriliser equipment in water supply
Surfaces - Direct irradiation of sterile cabinet surfaces (LFC)`

19
Q

Disadvantages of UV radiation

A

Hazard to operators as they are also irradiated
- use reflectors to protect operator and direct and intensify UV exposure to defined areas

Poor penetration
Shielding and reflection

20
Q

GAMMA IRRADIATION

A
  • High energy, powerful and penetrating electromagnetic radiation
  • shorter wavelength than X-rays
  • Emitted by decaying unstable nucleus (cobalt 60 - unstable radioactive form of cobalt 59)
  • ionisation of vital cell components and cell death –> ionisation of DNA, ionisation of cell water and produce free radicals to react with DNA
    Biological Indicator: B. Pumilus

used in: drugs in dry state i.e. freeze dried antibiotics, vaccines, oil, creams

Factors:
Amount of energy absorbed
Oxygen
Temperature
Organic substances (protective)
21
Q

Advantages of Radiation

A
  • materials not wetted or heated
  • operated at ambient temps (not extreme heat)
  • packed and sealed container in packaging
  • continuous and automated
22
Q

Disadvantages

A
  • Hazardous
  • chemical changes in drug
  • container deterioration
  • small volume, low density
  • expensive, needs a plant
23
Q

Chemical Sterilisation

A

Ethylene Oxide
Formaldehyde
Glutaldehyde

MOA

  • alkylating agents
  • Addition of hydrocarbons to reactive groups of protein molecules
  • acts on cell during DNA replication
  • Biocidal, mutagenic, carcinogenic
24
Q

Ethylene Oxide

A 
Flammable
Highly explosive
used with inert diluent gases as non-flammable mixture
highly diffusable through packaging
freely soluble in water
dissolve in rubber, plastic

Uses: dressings, containers, equipment, implants e.g. breast implants

25
Q

Factors affecting ethylene oxide sterilisation

A

Concentration
Temperature
Moisture - dissolves gas to form conc solution for optimal effect at 33% RH

26
Q

Monitoring of ethylene oxide

A

Thermocouples
Humidity sensors
Chemical indicators - strip changes colours on exposure
Biological indicators - attest vials, spore strips, indicator organisms B. subtilis var niger

27
Q

Limitations of ethylene oxide

A

Toxicity - carcinogenic
Difficult to monitor
Removal of residues
Time consuming

28
Q

Sterilisation by filtration

A
  • liquid and gas substances are removed by filters
  • no killing and no growth inhibited, only physical removal
Use:
Cleanroom air supply, LFC
heat labile liquids
heat labile ointments
QC tests using membrane filtration method
purification of water
29
Q

Desired properties of filters

A 
Inert
Non-pyrogenic
Efficiently removes particles
Good flow rate
Resistant to clogging
Sterilisable
Reusable
Do not retain drug
Do not release filter components
30
Q

Depth Filters

A

Compacted pads of fibres with pores and channels or variable diameters and directions
Eg HEPA filters
Mechanism:
Sieving, adsorption, retention
Under vacuum or positive pressure to assist flow
Arrest depends on size, charge, velocity of particles
High porosity
Good pore size range
Good dirt handling capacity

31
Q

Depth Filters Limitations

A
  • Need uniform pressure, if too high pressure, filter compress and decrease flow rate
  • Retain liquid in filter = loss of solvent, can not suck out liquid in filter otherwise filter will crack
  • loss of formulation ingredients
  • slow speed of sterilisation
  • may not be suitable for sterilisation or reuse
  • filter fibres may shed into filtrate
32
Q

Membrane Filters

A 
Polymeric membranes (one layer)
Hydrophilic, hydrophobic, solvent resistant, gridded
High porosity
Fast flow and speed
Low fluid retention
no shedding
Minimum solute adsorption
narrow pore size range
Poor dirt handling capacity
rapidly clogging

Uses: screening/ sieving, retention, all particles greater than pore size retained

33
Q

Monitoring Filters

A

Bubble point pressure test

Bacterial retention test (microbial challenge test)

34
Q

Bubble point pressure

A
  • the pressure of a test gas (N2) to push liquid out of a wet membrane filter
  • gas bubbles appear in liquid at that pressure
  • gas pressure is a measure of pore diameter
  • smaller pore size requires higher pressure (to overcome surface tension)
    Pass filter integrity test if bubble pressure is >/= to recommended pressure i.e. actual pore size is = or < specified test
35
Q

Microbial Challenge/ retention test

A

Test efficiency of sterilising filter (0.22um) using a challenge organism Br. diminuta 0.3um size in high conc
slow filtration then the entire filtration is cultured in broth medium, or filtered again and culture the filter
Filter passes if no growth after 72 hours at 30 deg

DD2 PAC3252 (10 decks)

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