Formaldehyde and glutaraldehyde are
used for disinfection orsterilization of instruments such as fiberoptic
endoscopes, respiratory therapy equipment, hemodialyzers, and dental
handpieces that cannot withstand exposure to the high temperatures of steam
sterilization. They are not corrosive for metal, plastic, or rubber. These
agents have a broad spectrum of activity against microor-ganisms and viruses.
They act by alkylation of chemical groups in proteins and nucleic acids.
Failures of disinfection or sterilization can occur as a result of dilution
below the known effective concen-tration, the presence of organic material, and
the failure of liquid to penetrate into small channels in the instruments.
Automatic circulating baths are available that increase penetration of
alde-hyde solution into the instrument while decreasing exposure of the
operator to irritating fumes.
is available as a 40% weight per volume solution in water (100% formalin). An 8% formaldehyde solution
in water has a broad spectrum of activity against bacteria, fungi, and viruses.
Sporicidal activity may take as long as 18 hours. Its rapid-ity of action is
increased by solution in 70% isopropanol. Formaldehyde solutions are used for
high-level disinfection of hemodialyzers, preparation of vaccines, and
preservation and embalming of tissues. The 4% formaldehyde (10% formalin)
solutions used for fixation of tissues and embalming may not be
Glutaraldehyde is a
dialdehyde (1,5-pentanedial). Solutions of 2% weight per volume glutaraldehyde
are most commonly used. The solution must be alkalinized to pH 7.4–8.5 for
are bactericidal, sporicidal, fungicidal, and virucidal for both lipophilic and
hydrophilic viruses. Glutaraldehyde has greater sporicidal activity than
formaldehyde, but its tubercu-locidal activity may be less. Lethal action
against mycobacteria and spores may require prolonged exposure. Once activated,
solutions have a shelf life of 14 days, after which polymerization reduces
activity. Other means of activation and stabilization can increase the shelf
life. Because glutaraldehyde solutions are frequently reused, the most common
reason for loss of activity is dilution and exposure to organic material. Test
strips to measure residual activ-ity are recommended.
Formaldehyde has a characteristic pungent odor and is highly irritating to respiratory mucous membranes and eyes at concentra-tions of 2–5 ppm. The United States Occupational Safety and Health Administration (OSHA) has declared that formaldehyde is a potential carcinogen and has established an employee exposure standard that limits the 8-hour time-weighted average (TWA) exposure to 0.75 ppm. Protection of health care workers from exposure to glutaraldehyde concentrations greater than 0.2 ppm is advisable. Increased air exchange, enclosure in hoods with exhausts, tight-fitting lids on exposure devices, and use of protec-tive personal equipment such as goggles, respirators, and gloves may be necessary to achieve these exposure limits.
Ortho-phthalaldehyde (OPA) is
a phenolic dialdehyde chem-ical sterilant with a spectrum of activity
comparable to glutaralde-hyde, although it is several times more rapidly
bactericidal. OPA solution typically contains 0.55% OPA. Its label claim is
that high-level disinfection can be achieved in 12 minutes at room temperature
compared with 45 minutes for 2.4% glutaraldehyde. Unlike glutaraldehyde, OPA
requires no activation, is less irritat-ing to mucous membranes, and does not
require exposure moni-toring. It has good materials compatibility and an
acceptable environmental safety profile. OPA is useful for disinfection or
sterilization of endoscopes, surgical instruments, and other medical devices.