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 1: guinea pigs challenged with VX

Abstract

Objective: This report, first in a series of five, directly compares the efficacy of 4 decontamination products and Skin Exposure Reduction Paste Against Chemical Warfare Agents (SERPACWA) in the haired guinea pig model following exposure to VX.

Methods: In all experiments, guinea pigs were close-clipped and given anesthesia. In the decontamination experiments, the animals were challenged with VX and decontaminated after a 2-minute delay for the standard procedure or at longer times for the delayed-decontamination experiments. Skin Exposure Reduction Paste Against Chemical Warfare Agents was applied as a thin coating (0.1 mm thick), allowed to dry for 15 minutes, and challenged with VX. After a 2-hour challenge, any remaining VX was blotted off the animal, but no additional decontamination was done. Positive control animals were challenged with VX in the same manner as the treated animals, except that they received no treatment. In addition, the positive control animals were always challenged with 5% VX in isopropyl alcohol (IPA) solution, whereas the treatment animals received either neat (undiluted) VX or 5% VX in IPA solution. 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 [LD(50)] of the treatment group divided by the LD(50) of the untreated positive control animals) was calculated from the probit dose-response curves established for each treatment group and nontreated control animals. Significance in this report was defined as p < .05.

Results: In the standard 2-minute neat VX decontamination experiments, the calculated PRs for Reactive Skin Decontamination Lotion (RSDL), 0.5% bleach, 1% soapy water, and the M291 Skin Decontamination Kit (SDK) were 66, 17, 16, and 1.1, respectively. Reactive Skin Decontamination Lotion was by far the most effective decontamination product tested and was significantly better than any of the other products. Bleach and soapy water provided equivalent and good (PR > 5) protection. They were both significantly better than the M291 SDK. The M291 SDK did not provide significant protection compared with positive controls. In the neat VX delayed-decontamination experiments, the calculated LT(50) (the delayed-decontamination time at which 50% of the animals died in the test population following a 5-LD(50) challenge) values for RSDL, 0.5% bleach, and 1% soapy water were 31, 48, and 26 minutes, respectively. The results showed that SERPACWA provided significant, but modest (PR < 5), protection against neat VX, with a PR of 2.1.

Conclusions: Several conclusions can be drawn from this study: 1) RSDL provided superior protection against VX compared with the other products tested; 2) 0.5% bleach and 1% soapy water were less effective than RSDL, but still provided good protection against VX; 3) the M291 SDK was the least effective decontamination product and did not provide significant protection against VX; 4) the agent was observed to streak when using the M291 SDK, and efficacy may improve if the agent is first blotted, followed by wiping with a new or clean part of the M291 SDK pad; 5) RSDL, 0.5% bleach, and 1% soapy water provided significant protection against a 5-LD(50) challenge of VX, even when decontamination was delayed for up to about 30 minutes; and 6) SERPACWA provided significant, but modest, protection against VX.