Sterilization Flashcards
Sources of contaminations
- Airborne
- Breath
- Skin
- Hair
- Clothing
- Surfaces
Methods to minimize contamination
- Airborne: use laminar airflow
- Breath: use masks
- Skin: nails must be scrubbed and hands and forearms washed with detergents
- Hair and clothing: wear sterile down over normal clothing, wear a cotton cap
- Working surfaces: clean with a bactericidal solution/ethyl alcohol
Definition of sterility
Absence of life; absolute freedom from biological contamination
Definition of sterilization
Inactivation/elimination of all viable organism and their spores
Definition of disinfectant
Substance used on non-living objects to render them non-infectious; kills vegetative bacteria, fungi, viruses but not spores e.g. formaldehyde
Definition of antiseptic
Substance used to prevent multiplication of microorganism when applied to living systems
Bacteriostatic in action but not necessarily bacteriocidal
Definition of bacteriostat
Substance which stops growth and multiplication of bacteria but does not necessarily kill them
Definition of bactericide
Substance that kills vegetative bacteria and some spores
Thermal death time
Time required to kill a particular organism under a given condition
What are the techniques for sterilization
- Steam sterilization
- Dry heat sterilization
- Filtration
- Gaseous
- Ionizing Radiation/Irradiation
Describe Steam sterilization
- Use steam under pressure in autoclaves
- Time, temp. 240C, pressure 20-30 lb
- Killing due to denaturation and coagulation of the microorganism’s proteins
- Highly effective, less time, inexpensive and large volumes
- therapeutic agent must be stable to water, heat
- Not for oily and moisture sensitive preparations
Applications for steam sterilization
- Solutions in ampoules
- vials
- instruments
- glassware
- surgical dressing
Describe dry heat sterilization
- No water used
- 160 - 170C for 2-4h in an oven
- Killing is due to dehydration of the microbial cells followed by slow oxidation
- Not for therapeutic agents that are thermolabile
Applications for dry heat sterilization
- Glassware
- Heat stable powders
- Paraffin
- Petrolatum
- Fixed oils
Describe filtration
- Physical removal of microorganisms by adsorption on the filter medium - filtration membrane
- Highly impt for sterilization of therapeutic agents especially heat sensitive materials
- Slow for large volumes and saturable (difficult to push a saturated material through the membrane)
- Membranes may absorb drug
Advantages of bacterial filtration
- Speed - in case of small volumes
- Ability to sterilize thermolabile materials
- Inexpensive
- Complete removal of living and dead microorganism and particulate matters
Describe gaseous sterilization
- Used mainly for heat and moisture sensitive materials
- Propylene oxide/ethylene oxide-carbon dioxide mixture at pressure 30 psi, temp 20-60C, 4-16h
Application of gaseous sterilization
- Thermolabile powder
- Polymers
- Ophthalmics
- Subcutaneous, vaginal inserts
- Plastic syringes
- Tubing sets
Disadvantages of gaseous sterilization
- Toxic
- gases are highly flammable
- explosive hazard
- not appropriate for solutions
Describe ionizing radiation/irradiation for sterilization
- Limited in use -> effect of radiation on containers and products
- Need highly specialized equipment: UV Lamp, ionization
- Mechanism: altering the chemicals within/supporting the microorganism to form deleterious new chemicals capable of destroying the cell
- Good for thermolabile material
How is sterility tests done?
- Organisms resistant to the method is used as the marker organism
- Choice of test method depends on the types of microorganisms involved
Marker organism for steam and ethylene oxide
Bacillus stearothermophilus
Marker organism for dry heat
Bacillus subtilis
What are pyrogens
Fever producing organic substances arising from contamination by bacteria, molds, viruses, and yeasts.
Causative material thought to be a lipopolysaccharide from the outer cell wall of the bacteria and endotoxins.
Removal of pyrogens
- Heating at high temp. (e.g. 250C for 45 mins)
- Reverse osmosis and ultrafiltration are excellent ways of removing pyrogen contamination from water
Testing for pyrogens
- Rabbit tests
- Limulus Amebocyte Lysate (LAL) Tests
Describe rabbit tests
- Render the syringes, needles and glassware free from pyrogens by heating at 250C for not less than 30 mins
- Warm the product to be tested to 37C plus/minus 2C
- Take 3 healthy rabbits and weigh and record temp
- Inject into an ear vein of each of 3 rabbits 10 ml of the product per kg body weight
- Record the temp at 1,2 and 3 hrs
- Material only meets the USP requirements for the absence of pyrogen if no rabbit shows an individual rise in temp at 0.6C or more above its respective control temp and sum of the temp. rises is less than 1.4C
- IF NOT, repeat tests using 5 other rabbits
- Material meets the USP requirements for the absence of pyrogens if not more than 3 of the 8 rabbits show individual rises in temp of more than or equal to 0.6C and sum of 8 individual temp. rises < 3.7C
Describe Limulus Amebocyte Lysate (LAL) Tests
- Extract from the blood cells of the Horse Shoe Crab (Limulus Polyphemus) contains an enzyme and protein that coagulates in the presence of low levels of lipopolysaccharides
- Considered more sensitive to endotoxin compared to the rabbit test
- Some products cannot be tested by LAL cos of API
Types of sterile products
- Systems and administration devices:
Dispersed systems - lipid microspheres, liposomes, microparticulates
Implants - bone growth, fertility controls, sustained delivery - Parenterals
- Ophthalmics
- Topicals
