Abstract  Clandestine bomb-makers are exposed to significant amounts of explosives and allied materials. As with any ingested xenobiotic substance, these compounds are subject to biotransformation. As such, the potential exists that characteristic suites of biomarkers may be produced and deposited in matrices that can be exploited for forensic and investigative purposes. However, before such assays can be developed, foundational data must be gathered regarding the toxicokinetics, fate, and transport of the resulting biomarkers within the body and in matrices such as urine, hair, nails, sweat, feces, and saliva. This report presents an in vitro method for simulation of human metabolic transformations using human liver microsomes and an assay applicable to representative nitro-explosives. Control and metabolized samples of TNT, RDX, HMX, and tetryl were analyzed using high-performance liquid chromatography coupled to tandem mass spectrometry (LC/MS/MS) and biomarkers identified for each. The challenges associated with this method arise from solubility issues and limitations imposed by instrumentation, specifically, modes of ionization.

Abstract  The tissue distribution. elimination, and metabolism of radioactivity were examined following a single oral administration of 14C-RDX, at a target dose of 45 mg/kg, to male and female Yucatan minipigs. Blood, urine, and feces were collected through 24 hours postdose. Blood, plasma, selected tissues, urine, and feces were analyzed for total radioactivity. Following dose administration, all animals vomited. Animals vomited at various times over the course of the study. Concentrations of 14C-RDX-derived radioactivity in plasma reached maximum levels (Cmax) at 12 hours postdose for both males and one female. Blood and plasma concentrations for the second female reached Cmax at 6 hours postdose. The plasma Cmax values for males ranged from 8.76 to 18.3 ug equivalents 14C-RDX/g, and in females values ranged from 8.54 to 10.0 ug equivalents 14C-RDX/g. The distribution of 14C-RDX-derived radioactivity was extensive, with drug derived radioactivity quantifiable in all analyzed tissues at 24 hours postdose. The highest concentrations of radioactivity were observed in liver, kidneys, and small intestine. The lowest values were observed in abdominal fat, skeletal muscle, and skin. Quantifiable levels of radioactivity in the brain and testes suggest 14C RDX derived radioactivity crosses the blood/brain and blood/testes barriers. Urine was the major route of elimination of 14C-RDX-derived radioactivity. At 24 hours postdose, urine and feces accounted for average values of 17.3 and 0.53% of the dosed radioactivity, respectively, in males and in females accounted for average values of 16.0 and 0.79% of the dosed radioactivity, respectively. The overall excretion recoveries in males and females were 40.6 and 29.7%, respectively. The relatively low levels of radioactivity observed in gastrointestinal contents and wash as well as low levels in feces suggest nearly complete oral absorption of 14C-RDX-derived radioactivity. Metabolite profiling and LC/MS/MS showed quantifiable levels of metabolites M1 (4-nitro-2,4-diazabutanal), M2 (4-nitro-2,4-diaza-butanamide), and parent RDX. All three metabolites were observed in urine, only RDX was observed in plasma. LC/MS/MS analysis of plasma showed trace amounts of RDX metabolites MNX, DNX, and TNX. Analysis also showed trace amounts of the metabolites MNX and DNX in male urine and MNX in female urine. RDX concentrations in the brains ranged from 33.5 to 1070 ng/g. RDX concentrations in liver were less than 1 ng/g.

Abstract  Male LACA mice were administered 3H-RDX orally or intravenously at dosages of 203.5 x 10(3)Bq(5.5[mu]Ci) per mouse and 112.85 x 10(3)Bq (3.05[mu]Ci contains 0.55mg RCX) per mouse. After administration, mice were sacrificed at different times. Tissues such as organs, blood, urine and feces were collected for testing. The test results demonstrated that 3H-RDX can be rapidly distributed through the blood to other tissues regardless of administration method. For oral administration, T1/2Ka = 5 min and T1/2 = 50.4 min. For intravenous administration, T1/2 = 9 min. In the case of intravenous administration, the order of 3H-RDX levels observed as a function of organ was: lung > heart > liver > kidney > brain > spleen > testicle > fat > muscle; in the case of oral administration, the order of 3H-RDX peak levels observed was: liver > kidney > muscle > lung > spleen > heart > brain > testicle > fat. It was also demonstrated that for both administration methods the radioactivity decreased significantly in 12-24 hours. Seven days after oral administration, the radioactivity in different organs dropped almost to background levels; after intravenous administration, mice immediately suffered from seizures, shock, etc, and recovered after 1.5 min. The RDX concentration in blood and brain tissue at the time was 1.57g/ml and 0.82g/g, respectively. When administered orally, the speed of 3H-RDX excretion via the urine was faster than via feces, at a ratio of 1.3:1. The total amount excreted via both urine and feces on day 1 was 64.82% of the total administered amount. The results suggest that 3H-RDX is widely distributed in mice and excreted via urine and feces. No significant 3H-RDX accumulation was observed in the tissues that were tested. Hexogen (RDX), i.e., cyclotrimethylene trinitramine, is a type of high explosive that is more powerful than TNT. It has been extensively used in the armament industry of our country. Hexogen is in the form of a white powder. The melting point is 203 oC. It is slightly soluble in water, not soluble in ether and carbon tetrachloride, and soluble in dimethylsulfoxide, acetone, cyclohexanone, hot aniline, phenol, and nitrobenzene[1]. It was earlier reported by Sanderman [2] that the oral LD50 for non-fasting rats was 200 mg/kg and 50-100 mg/kg for fasting rats. Most of the RDX was excreted in its original form via feces within three weeks, and only 1-2% was excreted via urine. It was reported by Skhlyanskaya [3] that the oral LD50 for mice is 500 mg/kg. If a dose of 20 mg/kg was orally administered for 30 consecutive days, mice gradually grew weaker and possibly died, however without demonstrating any nervous system symptoms. It was reported by Von Ottingen [5] that the oral LD50 for rats is 200 mg/kg; no intoxication was observed if a dose of 15mg/kg was fed daily to rats for 3 months. Schneider [4] recently reported the distribution and metabolism of RDX in rats and piglets and demonstrated that RDX was distributed evenly in animals and had no accumulating organs. Sun [6] also proved that RDX has no significant accumulation in rats, however, significant degeneration of nerve cells and a series of pathological changes in lung, heart, liver, gastrointestinal and testicular tissue occurred in fatally intoxicated animals. In order to further explore the effects of RDX on the body and clarify how RDX is absorbed, distributed and excreted, a study was conducted using oral and intravenous administration of 3H-RDX in mice.

Abstract  Given the potent carcinogenic effects of most N-nitroso compounds, the reductive transformation of the common explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) to a group of N-nitroso derivatives, hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX), hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX), and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX) in the environment have caused concerns among the general public. Questions are arising about whether the same transformations also occur in mammals, and if true, to what extent. This study investigated the N-nitroso derivatives production in the deer mouse GI tract following RDX administration. Findings verified that such transformations do occur in the mammalian GI tract at notable levels: the average MNX concentrations in deer mice stomach were 85 microg/kg and 1318 microg/kg for exposure to 10 mg/kg and 100 mg/kg diet, respectively. DNX in stomach were 217 microg/kg for the 10 mg/kg dose group and 498 microg/kg for the 100mg/kg dose group. Changes in other toxic endpoints including body weight gain, food consumption, organ weight, and behavior were also reported.

Abstract  Cyclotrimethylenetrinitramine (RDX), a compound used widely in bursting-type munitions, is a concern for the U.S. Department of Defense because it has been detected in soil and groundwater at military installations. Dermal absorption of 14C-RDX from acetone solutions and from two different soils was studied using excised human skin (from surgery) in flow-through diffusion cells. RDX in acetone (10 μL) or in soils (10 mg) was applied to the epidermal surface of the skin (0.64 cm2) and allowed to transverse the skin and become dissolved in a reservoir of receptor fluid that was maintained in contact with the dermal surface. The reservoir was of the flow-through type and receptor fluid was pumped at a rate of 1.5 mL/h. Receptor fluid was collected every 6 h for 24 h. Because the bioavailability of a chemical from soils depends on soil composition, dermal absorption of 14C-RDX from both a low-carbon (1.9%) and a high-carbon (9.5%) soil was assessed. At the conclusion of the experiment, the RDX remaining on the skin was washed with soap and water using cotton swabs, and the radioactivity present in washings was determined. The stratum corneum was removed from the deeper epidermis and radioactivity found in that layer was not considered in calculations of dermal absorption. The dermal absorption of RDX was relatively low. Only about 5.7 ± 1.9% of the RDX that had been applied in acetone was found in the skin (epidermis and dermis) (3.2 ± 1.9) and receptor fluid (2.5 ± 1.8) combined (over the full 24-h duration of the study). The levels of RDX found in the skin layers were stratum corneum 2.1%, epidermis 0.83%, and dermis 0.45%. The total recovery of applied dose (receptor fluid, skin, and washings) was about 80%. The extent of RDX absorption from soil was even lower than from acetone. Approximately 2.6 ± 1.1% of the RDX applied in the low-carbon soil and 1.4 ± 0.41% applied in the high-carbon soil was found in receptor fluid and skin in 24 h. The total recovery of the applied dose (receptor fluid, skin, and washings) was about 87% for the low-carbon soil and 94% for the high-carbon soil. Thus, the dermal absorption of RDX from soils was reduced considerably when compared with absorption from acetone and absorption was lower in the high-carbon soil than in the low-carbon soil.

Abstract  Water plays a key role in enhancing the permeability of human skin to many substances. To further understand its ability to potentially increase the bioavailabililty of soil contaminants, artificial sweat was applied to excised pig skin prior to dosing with munition-contaminated soils. Skin was mounted in chambers to allow simultaneous measurement of evaporation and penetration and to control air flow, which changed the dwell time of skin surface water within a l-h period post application of test materials. Additional variables included type of compound, aging of spiked soil samples, and carbon content of soil. To this end, the evaporation and skin penetration of C-14 labeled hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 2,6-dinitrotoluene (26DNT), and 2,4,6-trinitrotoluene (TNT) were determined from two soil types, Yolo, having 1.2% carbon, and Tinker, having 9.5% carbon. RDX soil samples aged 27 mo and 62 mo were compared to freshly spiked soils samples. Similarly, 26DNT samples aged 35-36 mo and TNT samples aged 18 mo were compared to freshly spiked samples. Approximately 10 μg/cm2 of radiolabeled compound was applied in 10 mg/cm2 of soil. Radiolabel recovered from the dermis and tissue culture media (receptor fluid) was summed to determine percent absorption from the soils. Radiolabel recovered from vapor traps determined evaporation. Mean skin absorption of all compounds was higher for low-carbon soil, regardless of soil age and skin surface water as affected by air flow conditions. For 26DNT, a simultaneous increase in evaporation and penetration with conditions that favored enhanced soil hydration of freshly prepared samples was consistent with a mechanism that involved water displacement of 26DNT from its binding sites. A mean penetration of 17.5 ± 3.6% was observed for 26DNT in low-carbon soil, which approached the value previously reported for acetone vehicle (24 ± 6%). 26DNT penetration was reduced to 0.35% under dryer conditions and to 0.08% when no sweat was applied. When soil hydration conditions were not varied from cell to cell, air flow that favored a longer water dwell time increased penetration, but not evaporation, consistent with a mechanism of enhanced skin permeability from a higher hydration state of the stratum corneum. Profiles of 26DNT penetration versus air flow conditions were exponential for freshly prepared soil samples, suggesting strong and weak binding sites; corresponding profiles of 26DNT penetration from aged samples were linear, suggesting a conversion of weak to strong binding sites. Absorption and evaporation was less than 5% for TNT and less than 1% for RDX, regardless of soil type and age. Fresh preparations of RDX in Tinker soil and aged samples of TNT in Yolo soil showed a significant decrease in skin absorption with loss of surface moisture. The penetration rate of radiolabel into the receptor fluid was highest during the 1-2 h interval after dosing with 26DNT or TNT. High-performance liquid chromatography (HPLC) analysis of 26DNT in receptor fluid at maximum flux indicated no metabolism or breakdown. For TNT, however, extensive conversion to monoamino derivatives and other metabolites was observed. Relatively little radioactivity was found in the dermis after 26DNT and TNT applications, and dermal extracts were therefore not analyzed by HPLC. RDX was not sufficiently absorbed from soils to allow HPLC analysis. This study has practical significance, as the use of water for dust control at remediation sites may have the unintended effect of increasing volatilization and subsequent absorption of soil contaminants. Soil in contact with sweaty skin may give the same result. Skin absorption of 26DNT from soil was over 50-fold higher than the value for dryer skin and over 200-fold higher than the value obtained when there was no sweat application. While the hydration effect was less dramatic for RDX and TNT, soil contaminants more closely matching the physical properties of 26DNT may be similarly affected by hydration.

Abstract  A unique metabolite with a molecular mass of 119 Da (C(2)H(5)N(3)O(3)) accumulated during biotransformation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by Rhodococcus sp. strain DN22 (D. Fournier, A. Halasz, J. C. Spain, P. Fiurasek, and J. Hawari, Appl. Environ. Microbiol. 68:166-172, 2002). The structure of the molecule and the reactions that led to its synthesis were not known. In the present study, we produced and purified the unknown metabolite by biotransformation of RDX with Rhodococcus sp. strain DN22 and identified the molecule as 4-nitro-2,4-diazabutanal using nuclear magnetic resonance and elemental analyses. Furthermore, we tested the hypothesis that a cytochrome P450 enzyme was responsible for RDX biotransformation by strain DN22. A cytochrome P450 2B4 from rabbit liver catalyzed a very similar biotransformation of RDX to 4-nitro-2,4-diazabutanal. Both the cytochrome P450 2B4 and intact cells of Rhodococcus sp. strain DN22 catalyzed the release of two nitrite ions from each reacted RDX molecule. A comparative study of cytochrome P450 2B4 and Rhodococcus sp. strain DN22 revealed substantial similarities in the product distribution and inhibition by cytochrome P450 inhibitors. The experimental evidence led us to propose that cytochrome P450 2B4 can catalyze two single electron transfers to RDX, thereby causing double denitration, which leads to spontaneous hydrolytic ring cleavage and decomposition to produce 4-nitro-2,4-diazabutanal. Our results provide strong evidence that a cytochrome P450 enzyme is the key enzyme responsible for RDX biotransformation by Rhodococcus sp. strain DN22.

Abstract  Toxicokinetic studies on the explosive RDX were conducted to develop environmental and health effects criteria. The absorption, distribution and elimination of 14C RDX were studies in rats following intratracheal administration. Rats were treated with 14C RDX (15 mg/kg, 5-6 microCi) in 1% carboxymethylcellulose suspension and placed in glass metabolism cages. Urine and feces were collected at 6-12 hr and 24 hr intervals, respectively, and radioactivity determined in a liquid scintillation counter. About 10% of the radioactivity appeared in the urine in 24 hr. In the first 4 and 6 days, respectively, females and males had eliminated 23% and 26% of the radioactive label via urine; in the same periods, excretion via the feces was 3% and 5%, respectively. After sacrifice of the rats at 4 or 6 days, the plasma levels of radioactivity were 0.02%/ml. The radioactive residues were 0.1%/g in liver, kidneys and lung, whereas brain and adipose tissus showed only 0.02%/g. The results indicate that a sizable fraction of RDX is eliminated in the urine, although considerable radioactive residues were detected in the liver, kidney, and lunug tissues after 4-6 days.

Abstract  Cyclotrimethylenetrinitramine (RDX) is an explosive extensively used by the military. It has caused convulsions in military field personnel ingesting it and in munition workers inhaling its dust during manufacture. At least one fatality was attributed to RDX toxicity in an European munitions manufacturing plant. In this country, RDX has been dumped into open pits for disposal after demilitarization, and in some instances has contaminated surface and ground water. It is possible that humans might be exposed to RDX in potable water. This study, initiated at the request of the Naval Medical Research and Development Command, was intended to determine the distribution, metabolism and excretion of RDX in laboratory animals and to estimate by inference the potential hazard to humans from RDX exposure.

Abstract  Absorption, distribution, and biotransformation are three critical aspects affecting toxicant action in animals. In this study, B6C3F1 mice (Mus musculus) were exposed for 28 days to contaminated feed that contained one of five different RDX concentrations: 0, 0.5, 5, 50, 500 mg/kg. RDX (Hexahydro-1,3,5-trinitro-1,3,5-triazine) and its reductive transformation products: MNX (hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine), DNX (hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine), and TNX (hexahydro-1,3,5-trinitroso-1,3,5-triazine) were quantified in stomach, intestine, plasma, liver, and brain of these mice. Average RDX concentrations followed a dose-dependent pattern for all matrices tested. No controls had concentrations above limits of detection. Average RDX concentrations in tissues of exposed mice ranged from 11.1 to 182 ng/mL, 25.6 to 3319 ng/g, 123 to 233 ng/g, 144 to 35900 ng/g, and 51.1 to 2697 ng/g in plasma, brain, liver, stomach, and intestine, respectively. A considerable amount of RDX was present in brain, especially in the highest exposure group. This is consistent with the widely observed central nervous system effects caused by GABA inhibition associated with RDX exposure. N-nitroso metabolites of RDX were also present in tested tissues in a dose-dependent pattern. Average MNX concentrations in the stomachs of mice exposed to RDX ranged from ND in control exposures to 490 ng/g in the highest exposure groups. MNX accumulated in brain at a maximum average concentration of 165.1 ng/g, suggesting the potential formation of MNX from RDX within the brain. DNX and TNX were present in stomach, plasma, and brain of mice at higher exposures. The presence of RDX metabolites at notable amounts in different tissues suggests RDX can transform into its N-nitroso metabolites in vivo by an undefined mechanism.

Abstract  Cyclotrimethylenetrinitramine (RDX), a commonly used military explosive, was detected as a contaminant of soil and water at Army facilities and ranges. This study was conducted to determine the relative oral bioavailability of RDX in contaminated soil and to develop a method to derive bioavailability adjustments for risk assessments using rodents. Adult male Sprague-Dawley rats preimplanted with femoral artery catheters were dosed orally with gelatin capsules containing either pure RDX or an equivalent amount of RDX in contaminated soils from Louisiana Army Ammunition Plant (LAAP) (2300 microg/g of soil) or Fort Meade (FM) (670 microg/g of soil). After dosing rats, blood samples were collected from catheters at 2-h intervals (2, 4, 6, 8, 10, and 12) and at 24 and 48 h. RDX levels in the blood were determined by gas chromatography. The results show that the peak absorption of RDX in blood was 6 h for neat RDX (1.24 mg/kg) and for RDX from contaminated soil (1.24 mg/kg) of LAAP. Rats dosed with RDX-contaminated FM soil (0.2 mg/kg) showed peak levels of RDX in blood at 6 h, whereas their counterparts that received an identical dose (0.2 mg/kg) of neat RDX showed peak absorption at 4 h. The blood levels of absorbed RDX from LAAP soil were about 25% less than for neat RDX, whereas the bioavailability of RDX from FM soils was about 15% less than that seen in rats treated with neat RDX (0.2 mg/kg). The oral bioavailability in rats fed RDX in LAAP soil and the FM soil was reduced with the neat compound but decrease in bioavailability varied with the soil type.

Abstract  This project is the first to investigate RDX metabolism in human liver. RDX metabolism was screened in human liver tissues including S9 preparations, microsomes, hepatocytes and several recombinant CYP450 isoforms under aerobic, anaerobic and oxygen reduced conditions. RDX metabolism was also conducted in several animal liver microsomes to compare with hum an liver microsomes. loss of the parent compound (RDX) was determined at 30 and 180 minutes of the incubation and ranked as human (46.6% & 51.8%)> rat (40.1% & 47.2%)> monkey (34.6% & 35.7%)> Pig (25.5% & 33.7%)> rabbit (11.6% & 18.0). The data is used to establish Physiologically-based pharm acokinetic (PBPK) models for human useful in risk assessment. Further characterization of the profiles of RDX in vitro metabolism in human and animal liver tissues is proposed. This study developed an in vitro metabolic model which mimics in vivo physiological condition and will be useful in the evaluation of human metabolic fate for novel energetics such as replacement formulations for RDX and for other toxic TICs/TIMs.

Abstract  The percutaneous absorption potentials of (14)C-labeled 2,4,6-trinitrotoluene (TNT), trinitrobenzene, 2,4-dinitrotoluene (2,4-DNT), 2,6-dinitrotoluene (2,6-DNT), 2-amino-4,6-dinitrotoluene, 4-amino-2,6-dinitrotoluene, 2,4-diamino-6-nitrotoluene, 2,6-diamino-4-nitrotoluene, N-methyl-N,2,4,6-tetranitrobenzamine, hexahydro-1,3,5-trinitro-1,3,5-triazine, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, and 2,2-thiobis(ethanol) were determined from two soil types, Yolo having 1.9% carbon and Tinker having 9.5% carbon. TNT skin absorption from another low-carbon soil (Umatilla) was also determined. Approximately 10 microg/cm(2) of radiolabeled compound was applied in 5 microl of acetone or 10 mg/cm(2) of soil to excised pigskin mounted in skin penetration-evaporation chambers. Absorption from acetone served as a control. Radiolabel recovered from the dermis and tissue culture media (receptor fluid) was summed to determine the percentage of absorption from the soils. For each compound, percentage absorptions of radiolabel were highest from acetone solution and lowest from Tinker soil, with the results from Yolo soil being intermediate. Skin absorptions of TNT from Yolo and Umatilla soils were similar. For TNT in all vehicles, the penetration rate of radiolabel into the receptor fluid was highest during the 1- to 2-h interval after dosing. HPLC analysis of TNT radiolabel in receptor fluid at maximum flux indicated extensive conversion to monoamino derivatives and other metabolites. For 2,4-DNT and 2,6-DNT applications in Yolo soil, percentage absorptions approached those obtained from acetone applications. After 2,4-DNT and 2,6-DNT applications (acetone and soils), HPLC analysis of radiolabel in receptor fluid during the period of maximum flux revealed no significant metabolites. Skin absorption of the nitro compounds from soils was found to correlate with the compound's water solubility and vapor pressure. These findings formed the basis of an empirical model to predict skin bioavailability.

Abstract  In rats injected ip with 500 mg of cyclotrimethylenetrinitramine (RDX)/kg, the respective mean times to first seizure and to death were 23.8 and 171.0 min, and the mean plasma concentrations of RDX at seizure and death were 5.2 and 13.8 microg/ml. Following 100 mg/kg po, the plasma concentration was 2.1 µ/ml at 4 hr and 3.0 µg/ml at 24 hr, while the urine concentration was 5.5 µg/ml at 4 hr and 6.9 µg/ml at 24 hr. In the 6 days following 50 mg/kg po, 0.7% was excreted as RDX in the feces and 2.4% in the urine. Irrespective of dosage or route of administration, the concentration of RDX was greatest in kidney, most variable in liver, and did not accumulate in the brain. Twenty-four hours after po dosing with 50 mg of [14C]RDX/kg, the liver and urine contained large amounts of RDX metabolites, and, after the first 4 days, 90% of the total radioactivity was recovered: 34% in the urine, 43% as 14CO2, 3% in the feces, and 10% in the carcass. In miniature swine dosed with 100 mg/kg po, the plasma concentration was 1.6 µg/ml at 2 hr and 4.7 µg/ml at 24 hr, while the urinary concentration was 2.0 µg/ml at 2 hr and 3.6 µg/ml at 24 hr. At 24 hr, the concentrations of RDX in brain, heart, liver, kidney cortex, kidney medulla, and fat were between 4.4 and 9.1 µg/g. Convulsions in pigs occurred 12-24 hr after dosing with RDX.

Abstract  A physiologically based pharmacokinetic (PBPK) model for simulating the kinetics of cyclotrimethylene trinitramine (RDX) in male rats was developed. The model consisted of five compartments interconnected by systemic circulation. The tissue uptake of RDX was described as a perfusion-limited process whereas hepatic clearance and gastrointestinal absorption were described as first-order processes. The physiological parameters for the rat were obtained from the literature whereas the tissue : blood partition coefficients were estimated on the basis of the tissue and blood composition as well as the lipophilicity characteristics of RDX (logP = 0.87). The tissue : blood partition coefficients (brain, 1.4; muscle, 1; fat, 7.55; liver, 1.2) obtained with this algorithmic approach were used without any adjustment, since a focused in vitro study indicated that the relative concentration of RDX in whole blood and plasma is about 1 : 1. An initial estimate of metabolic clearance of RDX (2.2 h(-1) kg(-1)) was obtained by fitting PBPK model simulations to the data on plasma kinetics in rats administered 5.5 mg kg(-1) i.v. The rat PBPK model without any further change in parameter values adequately simulated the blood kinetic data for RDX at much lower doses (0.77 and 1.04 mg (-1) i.v.), collected in this study. The same model, with the incorporation of a first order oral absorption rate constant (K(a) 0.75 h(-1)), reproduced the blood kinetics of RDX in rats receiving a single gavage dose of 1.53 or 2.02 mg kg(-1). Additionally, the model simulated the plasma and blood kinetics of orally administered RDX at a higher dose (100 mg kg(-1)) or lower doses (0.2 or 1.24 mg kg(-1)) in male rats. Overall, the rat PBPK model for RDX with its parameters adequately simulates the blood and plasma kinetic data, obtained following i.v. doses ranging from 0.77 to 5.5 mg kg(-1) as well as oral doses ranging from 0.2 to 100 mg kg(-1).

Abstract  Rats were either dosed with unlabeled cyclotrimethylenetrinitramine (RDX) or [14C]RDX by gavage at 20 mg/kg/day for up to 90 days or allowed free access to unlabeled RDX or [14C]RDX-saturated drinking water (50-70 microg/ml) for up to 90 days. RDX did not accumulate in any tissue examined in these studies, nor were there any tendencies for plasma (RDX) to increase continuously with repeated dosing. In the 90-day drinking water study the daily recovery of the 14C label, estimated at the end of 1, 4, 8, and 13 weeks, varied between 54 and 89%. The majority of the label was excreted as exhaled 14CO2 and as unidentified metabolites in the urine. Residual carcass radioactivity in the drinking water study did increase threefold from Week 1 to Week 13. While no overt neurological signs characteristic of RDX toxicity occurred in any of the treated rats, 8 of 30 rats dosed with 20 mg/kg/day died, apparently from exacerbation of chronic respiratory disease. Compared with results from other animal studies, these data support an ingestion limit of 0.1 mg of RDX/kg/day, or an acceptable level of 2 to 3 ppm in potable water.

Abstract  The study reported herein examined the metabolism of 14C-labeled hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) resulting from a single oral gavage of 5 ml/kg to male and female Yucatan miniature pigs (43 mg/kg, 56 microCi/kg in 0.5% carboxymethylcellulose in water). Blood, urine, and feces were collected at selected times of 1, 6, 12, and 24 h postdose. At 24 h postdose, liver samples were collected. Blood, plasma, liver, and excreta were analyzed for total RDX-derived radioactivity and metabolites were identified. Urine was the major route of elimination of 14C-RDX-derived radioactivity in both males and females. Relatively low levels of radioactivity were found in gastrointestinal contents and in feces, suggesting nearly complete absorption of 14C-RDX following an oral dose. Analysis of urine by liquid chromatography-mass spectrometry (LC/MS) identified quantifiable levels of two ring-cleavage metabolites, 4-nitro-2,4-diazabutanal and 4-nitro-2,4-diaza-butanamide, as well as parent RDX. The 4-nitro-2,4-diazabutanal, was seen in earlier studies of aerobic metabolism of RDX. The 4-nitro-2,4-diaza-butanamide, an amide, was not previously reported but was tentatively identified in this study. Analysis by a more sensitive method (LC/MS/MS) also showed trace amounts of the RDX metabolites 1-nitroso-3,5-dinitro-1,3,5-triazacyclohexane (MNX) (in both male and female urine) and 1-nitro-3,5-dinitroso-1,3,5-triazacyclohexane (DNX) (in male urine). Analysis of plasma by LC/MS/MS also revealed quantifiable levels of RDX and trace levels of MNX, DNX, and 1,3,5-trinitroso-1,3,5-triazacyclohexane (TNX). None of the liver extracts showed quantifiable levels of RDX or any identifiable metabolites. Most of the radioactivity was in the form of water-soluble high-molecular-weight compounds. RDX when given orally to pigs was rapidly metabolized by loss of two nitro groups followed by ring cleavage.