Is OPA the Same as Glutaraldehyde?

OPA, o-phthalaldehyde is one of the new replacements for glutaraldehyde in high level liquid disinfection. OPA shares many chemical similarities to glutaraldehyde and has similar toxicity, but the lower vapor pressure reduce the smell and vapor concentrations.

Glutaraldehyde has been used used as a high level disinfectant in healthcare for decades, particularly for endoscopes and other immersible items that need to be disinfected and turned around quickly. Glutaraldehyde is a very effective disinfectant but in recent years it has fallen out of favor because of eye, skin and respiratory irritation, sensitivity and occupational asthma. Glutaraldehyde has even been eliminated completely from use in the UK's National health service.

There are two main classes of chemical used for high level disinfection, the aldehydes and the oxidizers. The latter includes peracetic acid, hydrogen peroxide and sodium hypochlorite and the race has been on to find alternatives to glutaraldehyde.

Glutarladehyde is a dialdehyde, i.e. it has two aldehyde groups. The aldehyde group is the -COH part of the molecule in organic chemistry. There have been numerous complaints of irritation, sensitivity and occupational asthma from users of glutaraldehyde and substitutes have been sought.

The obvious substitutes are other dialdehydes such as OPA (shown below). Other dialdehydes, such as succinic dialdehyde have also been considered as high level disinfectants however succinic dialdehyde is not on the FDA's list of approved sterilants and disinfectants. These dialdehydes generally have similar chemical properties to glutaraldehyde and function similarly. Disinfection is achieved by their ability to cross link and hence inactivate proteins.
                                     

    Glutaraldehyde                                  OPA

The most successful dialdehdyde substitute for glutaraldehyde is OPA which is now sold as a replacement for glutaraldehyde. OPA has the advantage that it a solid compared to liquid glutaraldehyde, though both are normally supplied in solution, and so a OPA has lower vapor pressure and much less smell than the pungent glutaraldehyde. In addition, OPA is more effective and so can be used at a lower concentration.

As can be seen from the two figures above, glutaraldehyde and OPA are structurally similar and so have similar chemical properties. On this basis similar occupational health effects have been anticipated.  The disinfection mechanism is similar and so similar health effects on exposure may be expected. the lower vapor pressure of the OPA has reduced the irritation to the eyes and respiratory system and has greatly reduced the objection to the strong smell of glutaraldehyde. However, as with glutaraldehyde, there have been reports of sensitization with OPA as well as occupational asthma and contact dermatitis. 

  
The use of glutaraldehyde has increased in recent years in the US with the widespread adoption of automatic reprocessors for endoscopes. This equipment significantly reduces the occupational exposure to the disinfectant. Even so, workers can still be exposed and measures should be taken to minimize exposure.

As with handling any high level disinfection or sterilant chemical, the basic methods to increase workplace safety are as follows:

• The reprocessor should be located in a well ventilated area, preferably with a local exhaust to remove any vapors that are released from the equipment.
• A continuous gas monitor for the chemical used should be installed to provide a warning in case the concentration gets too high (leak, malfunction of the reprocessor, or ventilation). Continuous gas monitors are available for peracetic acid and hydrogen peroxide from ChemDAQ. For those compounds for which a continuous gas monitor is not available, regular air sampling should be performed where the operators work to check the vapor concentrations.
• The operators should be provided with suitable personal protective equipment (PPE), including gloves, masks, and perhaps respirators depending on the circumstances.
• The operators must be trained on the safe use of the chemicals and equipment they are using. This training should include an understanding of the chemical hazards, how to recognize exposure if it occurs, and what they should do to prevent exposure (just part of the training that they should receive under OSHA's Hazcom standard.).