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 carcinogenic.
OPA is very toxic to aquatic organisms and forms toxic biodegradation by-products; bio-accumulation is not reported.
Here’s how we would score OPA on the key decision making criteria:
• 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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