Pharmaceutical Sterilization Techniques

Sterilization

• Sterilization is the complete destruction or removal of all living microorganisms within a system, including bacteria, viruses, fungi, and spores.
• Spores are more resistant to heat and most disinfectants than non-sporing microorganisms.
• Critical in medical, laboratory, and food preparation settings to prevent infection, contamination, and ensure safety.
• Sterile is an absolute term; a system is either sterile or non-sterile.

Methods of Sterilization

• Physical methods:
  • Heat
  • UV
  • Ionizing radiation
  • Filtration
• Chemical methods:
  • Gas agents
  • Liquid agents (sterilants)
• Sterilant: A material or method used to remove or kill all microbes.

Factors Affecting Sterilization Effectiveness

• Type of microorganism: Some are harder to kill.
• Number of microorganisms: Fewer microbes are easier to eliminate.
• Amount and type of organic material: Blood or tissue acts as a shield.
• Number of cracks and crevices: Microorganisms can harbor in these areas.

Additional Factors

• Choice of the right sterilization method
• Temperature
• Exposure time
• Concentration of the sterilizing material
• pH and environmental conditions
• Load configuration
• Validation and monitoring of the sterilization method

Sterilization by Dry Heat

• Dry heat sterilization works by oxidizing microbial proteins.
• Requires longer exposure times and high temperatures
• USP and BP specify different temperature/time combinations for effective sterilization:
  • 160°C (320°F) for 2 hours
  • 170°C (338°F) for 1 hour
  • 180°C (356°F) for 30 minutes
• Techniques used include:
  • Direct flaming
  • Incineration
  • Hot air sterilization

Hot Air Oven

• Typical construction includes an outer metal shell, an insulated inner chamber, and adjustable shelves/racks.
• Heating mechanisms use electric elements, usually located at the bottom or sides of the oven.
• A thermostat controls the temperature for consistent heating.
• Forced air circulation ensures even temperature distribution.
• Temperature monitoring involves internal/external thermometers with digital displays and regular calibration.
• The oven has a tightly sealed door to prevent heat loss.

Infra-red Conveyor Oven

• Infra-red is a thermal radiation that converts absorbed energy into heat.
• Infra-red ovens use radiant heat.
• The conveyor belt ensures even exposure of items to infrared radiation.
• The infrared sources are concentrated at the entrance of the tunnel to heat quickly and suitably spaced.
• Effective sterilization requires high temperatures (typically above 160°C/320°F) for a precise duration.

Infra-Red Vacuum Oven

• It overcomes the limitations of air heating/cooling during sterilization.
• It uses infra-red radiation for heat transfer without a carrier.
• This makes it suitable for use in a vacuum

Use of Vacuum

• Allows quicker heating (as no heat is lost to the air).
• Enhances temperature stability (absence of convection currents).
• Minimizes oxidation of metal instruments.
• Allows uniform heat distribution in the vacuum environment

Important Considerations

• Exposure time only begins when the sterilizer reaches target temperature.
• Do not overload the sterilizer to improve heat convection and avoid long sterilization cycles.
• Use sterile instruments immediately; wrap in paper or muslin for storage in a dry, sterile container with a tight lid.

Applications of Dry Heat Sterilization

• Glassware (flasks, beakers, tubes, containers, pipettes, Petri dishes)
• Porcelain and metal articles (mortars, pestles, stainless steel dishes, scissors, scalpels, ointment tubes)
• Oils and similar anhydrous materials (ointment bases, paraffin, wool alcohols, bees wax)

Advantage of Dry Heat Sterilization

• Effectiveness against a range of microorganisms (bacteria, viruses, fungi, spores).
• Non-corrosive to metal instruments.
• Leaves no toxic residues.

Disadvantages of Dry Heat Sterilization

• Longer sterilization times than moist heat methods
• Requires higher temperatures.
• Less effective in penetrating porous materials, or materials with intricate designs
• Risk of damaging heat-sensitive materials
• Requires proper loading and careful monitoring to avoid issues like overheating.
• Not suitable for heat-sensitive materials like plastics, wood, rubber

Sterilization by Moist Heat

• Steam, as a sterilizing agent, transfers heat more efficiently than dry heat.
• Moisture from steam denatures proteins and disrupts cellular structures, leading to the destruction of microorganisms (bacteria, spores).
• Greasy/resistant protective layers of microorganisms can be softened by steam, facilitating the coagulation of interior portions.

Autoclaving

• A sterilization method that uses steam under pressure to achieve higher temperatures than boiling water.
• Official conditions for autoclaving vary (e.g., 115-116°C x 30 minutes).
• Elevated temperature/pressure is important for complete sterilization, especially of spores.

Autoclave Types

• Stationary: Large and fixed devices for sterilizing various equipment, tools, and materials.
• Portable: Vertical or horizontal cylinders with a lid, commonly for smaller volumes.

Autoclave Controls

• A vent expels air.
• A pressure gauge monitors pressure in the chamber.
• A safety valve lets excess steam exit.
• Temperature sensors monitor and regulate temperature during the sterilization cycle.

Autoclave Cycle

• Pre-sterilization phase: loading materials and air removal
• Sterilization phase: maintain temperature (121°C/134°C) for a specified time.
• Depressurization phase: slowly reducing pressure to atmospheric pressure.
• Cooling and drying phases: remove moisture from non-liquid items.
• Unloading phase: Sterilized materials are removed.

Advantages of Moist Heat Sterilization

• High effectiveness at killing micro-organisms (including spores).
• Suitable for a range of materials and items.
• Consistent and reliable sterilization results.
• Low toxicity, no residues.
• Lower temperature requirement.
• Enhanced penetration

Limitations of Moist Heat Sterilization

• Materials/items that are damaged by heat or moisture.
• Size limitations (large items or complex equipment that can't fit into smaller autoclaves).
• Biofilm or soil residue can shield microbes from the steam, making sterilization ineffective
• Corrosion risk for certain metal instruments
• Potentially longer cycle times

Pasteurization

• Heat treatment designed to kill or inactivate harmful microorganisms in liquids and specific foods without significantly affecting taste/quality.
• Introduced by Pasteur to stop wine spoilage due to specific bacteria.
• Process: heating the liquid/food to a set temperature for a specific time and then rapidly cooling.
• Types: LTLT (batch), HTST (continuous), UHT, Flash, ESL.