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.
Formaldehyde 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 mycobactericidal.
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 activation.
Activated solutions 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.