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Skin Exposure Paste

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Skin Exposure Paste

Discontinued Warning IconPlease Note: This Brand Name drug is no longer available in the US.
(Generic versions may still be available.)

CLINICAL PHARMACOLOGY

SERPACWA is not absorbed through intact human skin in detectable amounts. The systemic absorption of SERPACWA was evaluated under simulated usage conditions. Subjects were exposed to SERPACWA for four hours daily for two consecutive days according to package directions. For one hour each day the subjects experienced a period of light exercise under Mission Oriented Protective Posture 2 (MOPP 2) conditions (Battle Dress Uniform overgarment and overboots worn). At the end of each 4 hour period the subjects were allowed to remove residual SERPACWA via showering. NMR analysis of urine samples for both organic (limit of detection 0.3ppm) and inorganic fluorine (limit of detection 2ppm) revealed no detectable levels of fluorine from either component of SERPACWA.

Pharmacology

Mechanism of Action

SERPACWA serves as a physical barrier that may reduce or delay exposure of skin to chemical warfare agents (CWA). SERPACWA has no other known action.

Nonclinical and Clinical Studies

Nonclinical Studies

In controlled laboratory studies on animals, SERPACWA has been shown to reduce or delay skin exposure to a variety of CWA including: sulfur mustard (HD), a blistering agent; the nerve agents soman (GD), thickened soman (TGD), and VX; T-2 mycotoxin, a skin necrosis agent; and CS, a lacrimating riot control gas.

In vitro, concentrated liquid sulfur mustard (HD) and thickened soman (TGD) did not penetrate a thin (0.15 mm) layer of SERPACWA covering M8 Chemical Agent Detector Paper after continuous exposure for more than six hours.

In vivo studies designed to assess penetration of CWA applied directly to the skin of anesthetized rabbits with and without SERPACWA pretreatment demonstrated limited, but significant, protection by SERPACWA against 4-hour challenges with sulfur mustard (HD), T-2 Toxin, soman (GD) and VX.

SERPACWA applied prior to a 4-hour challenge with 1 Ál liquid sulfur mustard (HD) substantially reduced the size of the lesions. Those lesions present at the SERPACWA-treated sites were less severe. Application of SERPACWA was also shown to block all macroscopic signs of dermal irritation 24 to 48 hours following a 6-hour challenge with T-2 toxin and signs of erythema following a 15 minute exposure to 1.0% CS.

Under controlled laboratory conditions the majority of anesthetized rabbits pretreated with SERPACWA survived a 4 hour challenge with lethal concentrations of soman (GD) or VX. In comparison, almost all animals died within 4 hours of soman (GD) or VX exposure in the absence of SERPACWA. Blood acetylcholinesterase (AChE) activity associated with exposure to soman (GD), thickened soman (TGD) or VX was significantly higher in most animals pretreated with SERPACWA compared to unprotected animals. However, almost all of the animals exposed to soman (GD), and approximately two-thirds of the animals exposed to VX experienced some loss of blood AChE activity, indicative of CWA penetration of the SERPACWA barrier.

The relevance of these studies in anesthetized animals under controlled conditions of SERPACWA application and exposure to CWA to actual field use conditions is not quantifiable. The limited, but significant, protection that was provided in animals was critically dependent on complete coverage of exposure sites. The barrier properties and safety of SERPACWA under conditions of wear time greater than 4 hours were not assessed.

The use of insect repellents containing DEET, some camouflage paints (loam and sand), and possibly permethrin, reduced but did not completely eliminate the protective effects of SERPACWA. Further testing showed that wiping off DEET with a dry towel prior to application of SERPACWA partially restored protection afforded by SERPACWA.

Clinical Studies

SERPACWA has been shown to reduce or delay exposure of skin to chemicals used as surrogates for chemical warfare agents in human trials. However, SERPACWA did not provide complete protection in every tested subject. These surrogates include methyl nicotinate, a skin irritant and vasodilator, and urushiol, a resin contained in plants like poison ivy.

A clinical study was performed to evaluate SERPACWA's ability to reduce the severity of dermatitis resulting from four hours of continuous contact with urushiol (poison ivy resin) in acetone solution in 50 healthy human volunteers with a history of sensitivity to urushiol. Subjects with a history of allergic reactions to glycols, cosmetics, or skin care products were excluded from this study. Sites on the ventral forearms of subjects were wiped with 70% isopropyl alcohol and allowed to air dry. Sites were pretreated with SERPACWA. One hour later, each subject had a matched pair of SERPACWA-pretreated and untreated sites exposed to equal volumes of a urushiol solution. To test SERPACWA at a range of urushiol doses, equal volumes of a more concentrated urushiol solution were applied to a different matched pair of SERPACWA-pretreated and untreated sites on each subject. The sites were left undisturbed for 4 hours, then washed off with a soapless cleanser and water. Based on photographs taken 4 days after urushiol challenge, two blinded physician observers independently scored the contact dermatitis severity, with a score of 0.0 corresponding to no reaction, and a score of 4.0 corresponding to a bullous, ulcerative reaction.

The following table shows the contact dermatitis scores recorded for the test sites.

  Number of Test Sites By Score
SERPACWA-treated Sites SERPACWA-untreated Sites
Scores After High Dose Challenge Scorer #1 Scorer #2 Scorer #1 Scorer #2
0 60 58 5 4
0.5 20 19 31 22
1.0 14 15 36  
1.5 1 2 12 22
2.0 1 1 9 14
2.5     3 4
3.0   1   3
3.5       4
4.0        
  SERPACWA-treated Sites SERPACWA-untreated Sites
Scores After Low Dose Challenge Scorer #1 Scorer #2 Scorer #1 Scorer #2
0 64 59 6 7
0.5 21 27 39 27
1.0 9 5 27 26
1.5 2 3 13 19
2.0     10 7
2.5   2 1 4
3.0       5
3.5       1

The contact dermatitis scores at each matched pair of SERPACWA-treated and SERPACWA-untreated sites were compared. The mean differences in the contact dermatitis scores were 0.7 to 1.0 point lower for sites pretreated with SERPACWA compared to matched sites not treated with SERPACWA. The degree to which SERPACWA reduced the development of dermatitis was varied among individuals, between the different observers, and between different urushiol dosages. Not all SERPACWA-treated subjects were completely protected from a urushiol reaction, but SDERPACWA-treated sites exhibited dermatitis scores lower than the SERPACWA-untreated matched sites. The observed reduction in contact dermatitis scores may not predict the degree of protection SERPACWA would provide to humans from exposure to CWA.

A clinical study was performed to determine whether perspiration, induced during the time interval between SERPACWA application and exposure of subjects to a cutaneous irritant, disrupted barrier properties of the product. Subjects with a history of allergic reactions to glycols, cosmetics, or skin care products were excluded from this study. SERPACWA was applied to selected sites on the ventral forearm skin of 37 healthy normal subjects, who were then exposed to conditions that induce active perspiration. Following this exposure, sites pretreated with SERPACWA and sites not treated with SERPACWA were challenged with the dermal irritant/vasodilator methyl nicotinate for 2 minutes. Intraindividual comparisons of laser Doppler velocimetry (LDV) measured at methyl nicotinate-challenged sites showed substantially less cutaneous vasodilation from methyl nicotinate exposure in SERPACWAB•treated sites compared to SERPACWA-untreated sites. Not all SERPACWA-treated sites were completely protected from methyl nicotinate-induced vasodilation. The degree to which SERPACWA reduced methyl nicotinate-induced vasodilation was variable among individuals. The LDV analysis was corroborated using a Draize visual scoring method. The observed reduction in LDV scores may not predict the degree of protection SERPACWA would provide to humans from exposure to CWA.

Last reviewed on RxList: 3/9/2009
This monograph has been modified to include the generic and brand name in many instances.

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