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| LETTER TO EDITOR |
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| Year : 1998 | Volume
: 46
| Issue : 3 | Page : 174-175 |
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Efficacy of paraformaldehyde tablets in sterilization of polyvinyl-chloride tubing
S Sharma
Correspondence Address:
S Sharma
 Source of Support: None, Conflict of Interest: None  | Check |
PMID: 10085634 
How to cite this article:
Sharma S. Efficacy of paraformaldehyde tablets in sterilization of polyvinyl-chloride tubing. Indian J Ophthalmol 1998;46:174-5 |
| Editor: | |  |
Antiseptics, disinfectants and sterilization procedures are important in preventing nosocomial infections. The choice of agents and procedures to be used depends on a variety of factors such as the degree of microbial killing required, the nature of the item to be treated and the cost and ease of using the available agents.
Formaldehyde, principally marketed as a water-based solution called Formalin (37% formaldehyde by weight), is a bactericide, tuberculocide, fungicide, virucide and sporicide.[1] It is a high-level disinfectant and sterilant in both its liquid and gaseous states. However, its use in hospital environments has been drastically reduced in the United States after the National Institute for Occupational Safety and Health indicated that formaldehyde should be handled as a potential carcinogen.[2] In our country, nevertheless, formaldehyde continues to be used extensively in the hospital environment for various purposes including operating room sterilization, decontamination of equipment, etc., apart from its wide usage in specimen preservation. One of the curious applications of this agent, prevalent in ophthalmic operation theatres in India, is in the form of tablets for the sterilization of cryopexy probes, crescent knives or blades, sharp keratomes and other sharp instruments that can be damaged by heat. These are available in the form of paraformaldehyde polymer of formaldehyde, as tablets of one gram each. A literature search did not provide adequate information regarding the efficacy of this form of formaldehyde in sterilization. Therefore, we decided to test the same. The study design is shown in the Figure.
Briefly, standard suspensions of Escherichia coli, Bacillus subtilis and Aspergillus flavus containing 10 8 cells (spores in case of A. flavus) per millilitre of phosphate buffered saline pH 7.4 (PBS) were used to artificially contaminate 27 pieces (1.5 meters each) of intravenous infusion tubing (polyvinyl chloride). Contamination was done by passing 1 ml of the microbial suspension through the full length of each tube using a syringe. The tubes were then flushed thoroughly with tap water and three tubes each were placed in airtight containers (20x15x15 cms) with either 5, 10 or 20 tablets of paraformaldehyde. At the end of 8, 16 and 24 hours one tube each was removed, flushed with 0.5 ml of sterile PBS, and the fluid from outlet was allowed to drop on sheep blood chocolate agar plates. The plates were incubated at 35°C for 48 hrs in the case of E. coli and B. subtilis and at 27°C for 4 days in the case of A. flaυus. The results are summarized in the Table.
While the vegetative form of bacteria (E. coli) was killed effectively within 8 hrs by exposure to as few as 5 tablets, the spore-bearing organisms (B. subtilis and A. flavus) required 24 hrs and more tablets. We conclude that with an adequate number of tablets (≥10), airtight containers and adequate exposure time (≥24 hours) the paraformaldehyde can effectively sterilize contaminated tubing or similar material.
However, this communication is not meant to recommend this procedure but only to emphasize that the use of paraformaldehyde tablets does result in effective sterilization. There always remains a risk of inadequate sterilization if the product is substandard and sufficient exposure time has not elapsed.
| References | | |
| 1. | Rutala WA. APIC guideline for selection and use of disinfectants. Am J Inf Control 1990; 18:99-117.  [ PUBMED] |
| 2. | National Institute of Occupational Safety and Health (U.S). Formaldehyde:evidence of carcinogenicity. NIOSH Current Intelligence Bulletin 34. Washington DC: Department of Health Education and welfare Publication ;15 April 1981. p 81-111. |
[Figure - 1]
[Table - 1]
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