Chemical methods of sterilization

Sterilization is the process of removing from objects (medical devices (MD), medicines, etc.) all kinds and forms of viable microorganisms.  Earl Spaulding was one of the first to talk about sterilization of medical devices. In 1957, he proposed the classification of instruments and devices into three categories (critical, semi-critical and non-critical) depending on the risk of infection of the patient. This separation made it possible to establish the required decontamination method. For example, various implants are classified as critical MD and are subject to sterilization, while endoscopes are semi-critical and require high level disinfection.

In general, sterilization methods can be divided into thermal (autoclavation, air sterilization), chemical (gases, antiseptic solutions), sterilization by filtering and radiation exposure. Chemical methods are mainly used for heat-sensitive and moisture-sensitive medical devices.

Some medical devices are enough to disinfect. Disinfection is a procedure that involves treating a microbial contaminated object aimed at destruction of the biggest possible amount of microbes so that they cannot  cause infection when using the MD. There are three main methods of disinfection: thermal, chemical and ultraviolet radiation.

If we talk about chemical methods of disinfection, the same chemical agents are used for sterilization, but the conditions of the procedure differ.

For example, hydrogen peroxide is a sterilizer for 6 hours of treatment (t = 20° C) and a high level disinfectant at a cycle length of 30 minutes (t = 20° C).

Sterilizants and disinfectants are subject to a number of certain requirements:

Broad spectrum: should have a wide antimicrobial spectrum

-Fast acting: should produce a rapid kill

-Not affected by environmental factors: should be active in the presence of organiс matter (e.g., blood, sputum, feces) and compatible with soaps, detergents, and other chemicals encountered in use

-Nontoxic: should not be harmful to the user or patient

-Surface compatibility: should not corrode instruments and metallic surfaces and should not cause the deterioration of cloth, rubber, plastics, and other materials

-Residual effect on treated surfaces: should leave an antimicrobial film on the treated surface

-Easy to use with clear label directions

-Odorless: should have a pleasant odor or no odor to facilitate its routine use

-Economical: should not be prohibitively high in cost

-Solubility: should be soluble in water

-Stability: should be stable in concentrate and use-dilution

-Environmentally friendly: should not damage the environment on disposal.

Perhaps none of the disinfectants-sterilizants completely meets all the above requirements. For example, peracetic acid and hydrogen peroxide cause corrosion of metal instruments, ethylene oxide – toxic to staff and patients and it is a carcinogen, gluteraldehyde has insufficient efficacy against certain microorganisms. Here is the table about advantages and disadvantages of the chemical sterilizants:

Sterilizants Examples of MD Advantages Disadvantages
Peracetic Acid/Hydrogen Peroxide Flexible endoscopes -No activation required

-Odor or irritation not significant

-Materials compatibility concerns (lead, brass, copper, zinc) both cosmetic and functional
Glutaraldehyde Hemodialyzers, endoscopes, laparoscopic plastic trocars – Relatively inexpensive

– Excellent materials compatibility

– Respiratory irritation from glutaraldehyde vapor

– Pungent and irritating odor- Relatively slow mycobactericidal activity

– Allergic contact dermatitis

Hydrogen Peroxide Soft lenses, breath endoscopes, -No activation required

-May enhance removal of organic matter and organisms

-No disposal issues

-No odor or irritation issues

-Inactivates Cryptosporidium

– Material compatibility concerns (brass, zinc, copper, and nickel/silver plating) both cosmetic and functional- Serious eye damage with contact
Orthophthalaldehyde Endoscopes – Fast acting high-level disinfectant

– No activation required

– Odor not significant

– Excellent materials compatibility claimed

– Stains skin, mucous membranes, clothing, and environmental surfaces

– Repeated exposure may result in hypersensitivity in some patients with bladder cancer

– More expensive than glutaraldehyde

– Eye irritation with contact

– Slow sporicidal activity

Peracetic Acid Endoscopes arthroscopes, surgical and dental instruments – Rapid sterilization cycle time (30-45 minutes)

– Environmentally friendly by-products (acetic acid, O2, H20)

– Compatible with many materials and instruments

– Potential material incompatibility (e.g., aluminum anodized coating becomes dull)- Used for immersible instruments only

–  One scope or a small number of instruments can be processed in a cycle

– More expensive (endoscope repairs, operating costs, purchase costs) than high-level disinfection

– Serious eye and skin damage (concentrated solution) with contact

The full text of this guideline can be found on the FDA website: https://www.cdc.gov/infectioncontrol/guidelines/disinfection/ 

References:

-Воробьев А. А., Быков А.С., Пашков Е.П., Рыбакова А.М. Микробиология Учебник. — 2-е изд., перераб. и доп. — М.: Медицина, 2003. — 336 с: ил. — (Учеб. лит.для студ. фарм. вузов). – ISBN 5-225-04411-5

-W. David Chang, Michael J. Brenner, Emily K. Shuman, Mimi S. Kokoska, Reprocessing Standards for Medical Devices and Equipment in Otolaryngology: Safe Practices for Scopes, Speculums, and Single-Use Devices, Otolaryngologic Clinics of North America, Volume 52, Issue 1, 2019, Pages 173-183.

-https://www.cdc.gov/infectioncontrol/guidelines/disinfection/