Efficacy studies of Reactive Skin Decontamination Lotion, M291 Skin Decontamination Kit, 0.5% bleach, 1% soapy water, and Skin Exposure Reduction Paste Against Chemical Warfare Agents, Part 2: Guinea pigs challenged with soman

Abstract

Objective: This report, the second in a series of five, directly compares the efficacy of Reactive Skin Decontamination Lotion (RSDL), the M291 Skin Decontamination Kit (SDK), 0.5% bleach (sodium or calcium hypochlorite solution), 1% soapy water, and Skin Exposure Reduction Paste Against Chemical Warfare Agents (SERPACWA) in the haired guinea pig model following exposure to soman (GD).

Methods: In all experiments, guinea pigs were close-clipped and given anesthesia. In the decontamination experiments, the animals were challenged with GD and decontaminated after a 2-minute delay for the standard procedure or at longer times for the delayed-decontamination experiments. Positive control animals were challenged with GD in the same manner as the treated animals, except that they received no treatment. All animals were observed during the first 4 hours and again at 24 hours after exposure for signs of toxicity and death. The protective ratio (PR, defined as the median lethal dose [LD₅₀] of the treatment group divided by the LD₅₀ of the untreated positive control animals) was calculated from the derived probit dose–response curves established for each treatment group and nontreated control animals. SERPACWA was applied as a thin coating (0.1 mm thick), allowed to dry for 15 minutes, and challenged with GD. After a 2-hour challenge, any remaining GD was blotted off the animal, but no additional decontamination was done. Significance in this report is defined as p <.05. Neat (undiluted) GD was used to challenge all animals in these studies.

Results: In the standard 2-minute GD decontamination experiments, the calculated PRs for RSDL, 0.5% bleach, 1% soapy water, and M291 SDK were 14, 2.7, 2.2, and 2.6, respectively. RSDL was by far the most effective decontamination product tested and significantly better than any of the other products. Bleach, soapy water, and the M291 SDK provided equivalent and modest protection. Since only RSDL provided at least good protection (PR > 5), it was the only decontamination product evaluated for delayed decontamination. In the GD delayed-decontamination experiments, the calculated LT₅₀ (the delayed-decontamination time at which 50% of the animals die in the test population following a 5-LD₅₀ challenge) value for RSDL was only 4.0 minutes.

Conclusions: Several conclusions can be drawn from this study: 1) Reactive Skin Decontamination Lotion provided superior protection against GD compared with the other products tested; 2) The 0.5% bleach solution, the 1% soapy water solution, and the M291 SDK were less effective than RSDL, but still provided modest (2 < PR < 5) protection against GD; 3) Reactive Skin Decontamination Lotion, the best product tested, did not provide significant protection against GD when decontamination was delayed for more than 3 minutes; 4) Skin Exposure Reduction Paste Against Chemical Warfare Agents provided significant, but modest, protection against GD; 5) There was good correlation between using the rabbit model and the guinea pig model for decontamination efficacy evaluations; and 6) Soman (GD) is an agent of real concern because it is very difficult to decontaminate and the effects ofexposure are difficult to treat.

Keywords::

• decontamination
• personnel decontamination
• skin decontamination
• delayed decontamination
• barrier skin creams
• Skin Exposure Reduction Paste Against Chemical Warfare Agents
• chemical warfare agents
• nerve agents
• soman

Acknowledgments

The opinions, interpretations, conclusions, and recommendations are those of the authors and are not necessarily endorsed by the U.S. Army or the Department of Defense.

The experimental protocol was approved by the Animal Care and Use Committee at the United States Army Medical Research Institute of Chemical Defense and all procedures were conducted in accordance with the principles stated in the Guide for the Care and Use of Laboratory Animals (National Research Council, Publication No. 85-23, 1996) and the Animal Welfare Act of 1966 (P.L. 89-544), as amended.

The use of trade names does not constitute an official endorsement or approval of the use of such commercial hardware or software. This document may not be cited for purposes of advertisement.

The authors wish to give a special thanks to our statistician, Ms. Robyn Lee. She provided expert guidance in selecting appropriate challenge doses and determining the required number of animals to establish rigorous dose-response curves. She also trained the authors to perform a probit analysis of the data using the SAS program and provided a critical review of the draft manuscript. Her dedication and assistance is greatly appreciated.

Declaration of interest

The authors report no declarations of interest.