Formaldehyde sterilisation

Food and Dmg and Cosmetic Act Device Amendment, 169 formaldehyde sterilisation, 160 Fourier transform infra-red-... 

Classical sterilisation techniques using an autoclave and saturated steam under pressure, hot water or dry heat are practical and reliable. Other reliable sterilisation methods include membrane filtration, ionising radiatirm sterilisation (gamma and electron-beam radiation) and gas sterilisation (ethylene oxide, formaldehyde). Sterilisation equipment (autoclaves, membrane filters, and other sterilisers) is often used in industrial manufacturing, in preparation in pharmacies, and in other healthcare establishments. Standard sterilisation processes are described in the Ph. Eur., in other current Pharmacopoeias, in ISO standards and National guidelines. 

One result of this development work is an instrument for accurately measuring a key property of can coatings, the sterilisation resistance. First, however, a brief description of can coatings and some of their properties is in order. The discussion will be limited to coatings to be applied to the interior of food-or beverage-containing cans since this application requires the highest chemical resistance. Most of the work described has been carried out with can lacquers of the solid epoxy resin/phenolic-formaldehyde (E/PF) type as these are the predominant type used in Western Europe. 

Although several gases will kill bacteria (ethylene oxide, formaldehyde, propylene oxide), ethylene oxide is the one which has been most widely adopted for pharmaceuticals, instruments, and dressings. Sterilisation by ethylene oxide involves either a gas concentration of 10-20% with an inert gas such as carbon dioxide or nitrogen, or the gas in a pure state. The dilution method is usually preferred, particularly as ethylene oxide can form an explosive mixture with air. 

Sterilisation by the use of gases usually involves either ethylene oxide or formaldehyde. Both are broad spectrum biocides but neither is as effective as heat. Both may be used for temperature sensitive systems. Both must be used under the correct conditions as they are toxic, and ethylene oxide is explosive when mixed with air. Ethylene oxide is highly penetrative, but formaldehyde is not and is generally used where surface sterility is required. 

Contamination by ablation may be exacerbated by migration of mineral oil from the vacuum pump towards the chamber.Under these conditions infectious particles could be encapsulated by the oil and protected from inactivation when gaseous biocides such as formaldehyde are used to sterilise the freeze-drier. 

Stoppered vials can be left in the chamber and exposed to a sterilising vapour in order to decontaminate the outside of the vials before their removal from the freeze-drier. In this laboratory we have been able to demonstrate that formaldehyde vapour will not permeate stoppered vials which contain freeze-dried samples. 

Gas sterilisation is performed with ethylene oxide or hydrogen peroxide gas. Sometimes peracetic acid is used, but this method is too specialised to mention here in detail. In the past (fi-om 1940) formaldehyde was used as well, but this method is rarely used anymore. Gas sterilisation is used for sterilisation of medical devices and of surfaces of pharmaceutical containers where the contents are too sensitive to the high temperature of steam sterilisation and/or cannot withstand radiation sterilisation. 

Ethylene oxide is extensively used for sterilisation of powders and it is sometimes necessary to determine residues. Methods which have been applied successfully depend on conversion of the residual ethylene oxide or glycol to formaldehyde and the determination of this product by the... 

To say that ethylene oxide sterilisation is the method of choice is also not universally accepted in England. I have made special representations to Dr. Kelsey of the Central Public Health Laboralories at Colindale on two occasions over the last four years. On both occasions he has produced more objections to ethylene oxide sterilisation than attractions. Dr. Kelsey has sent me considerable literature and references in his own work against the efficacy of ethylene oxide sterilisation. Rather than support the use of ethylene oxide sterilisation Dr. Kelsey apparently would prefer to popularise sterilisation by low temperature steam combined with formaldehyde vapour for plastics materials and other substances likely to be damaged by dry heat or conventional autoclaving. 

Soil sterilisation has proved of particular value for controlling the damping-off diseases which are so destructive to seedlings. It Is also generally" recommended for the prevention of truck-crop diseases , such as scurf, black-rot, and stem-rot of sweet potatoes . Sterilization may be accomplished by drenching the soil with a solution of 1 pint of 37 per cent formaldehyde in 12.5 gallons of water and then co e ing with burlap or paper for... 

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