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Disinfectant Chemistry Report Card #11 – Ortho-Phthalaldehyde (OPA) - the "safer" aldehyde

Ortho-phthalaldehyde (OPA) has been around since the
early 1990s as a safer disinfectant active for treating instruments and devices,
in comparison to glutaraldehyde. OPA is found to be very compatible with most
materials used to manufacturer medical instruments. Contrary to common belief,
OPA is one of the members of the aldehyde family that does not have the
characteristic pungent odor associated with formaldehyde etc. OPA is known to
maintain its biocidal activity in a wide range of pH, while being compatible
with various materials and equipment.
OPA causes malfunction of the bacterial cell membrane by
attaching to protein residues and receptors and which also increases the
permeability to OPA allowing the chemical to enter the cell.  Once in the cell, OPA interacts with enzymes
and RNA and thus causes failure of cellular functions, which leads to bacterial
cell death.  OPA at various use dilution
is known to be a bactericide, virucide, fungicide, and tuberculocide and is
widely used as a high level disinfectant for reprocessing semi-critical medical
devices (e.g. items that will come in contact with mucous membranes or
non-intact skin). Sporicidal activity OPA is very limited and dependent on the
pH and the contact time is considered to be too long to be useful for
reprocessing activities.
At use dilution of 0.5% to 5%, OPA does not impose any
flammability or reactivity hazards. There has been reports of residual OPA
exposure from endoscopes and trans-esophageal probes to patients, where it has
caused exacerbation of asthma and bronchitis, and general sensitization. At use
dilution, OPA is found to be a sensitizer to eye, skin and respiratory organs,
however, current scientific evidence has not found OPA to be mutagenic or

OPA is very toxic to aquatic organisms and forms toxic
biodegradation by-products; bio-accumulation is not repo
Here’s how we would score OPA on the key decision making
Speed of Disinfection – A to D

o High Level Disinfection within 5 – 12 minutes
o Sporicidal contact time prohibitive to use as a
chemical sterilant
Spectrum of Kill – A

o Achieves disinfection against all microorganisms;
bacteria, viruses, fungi, mycobacteria and spores
Cleaning Effectiveness – N/A

o No detergent properties
o High Level Disinfection and Chemical Sterilization
requires instruments to cleaned prior to moving to the disinfection or
sterilization process

Safety Profile – C

o Minimal long term toxicity data
o OPA has been contraindicated for use on urological instruments
due to anaphylaxis
Environmental Profile – D

o Restrictions in disposal
Cost Effectiveness – B to C

o The original patent for OPA has expired and is now
available from a number of suppliers
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