Pharmacokinetics and pharmacodynamics of standard nerve agent medical countermeasures in Göttingen Minipigs

Animal research continues to serve a critical role in the testing and development of medical countermeasures. The Göttingen minipig, developed for laboratory research, may provide many benefits for addressing research questions within chemical defense. Targeted development of the Göttingen minipig model could reduce reliance upon non-human primates, and improve study design, statistical power, and throughput to advance medical countermeasures for regulatory approval and fielding. In this vein, we completed foundational pharmacokinetics and physiological safety studies of intramuscularly administered atropine sulfate, pralidoxime chloride (2-PAM), and diazepam across a broad range of doses (1-6 autoinjector equivalent) using adult male Göttingen minipigs (n=11; n=4-8/study) surgically implanted with vascular access ports and telemetric devices to monitor cardiovascular, respiratory, arterial pressure, and temperature signals. Pharmacokinetic data were orderly and the concentration maximum mirrored available human data at comparably scaled doses clearly for atropine, moderately for 2-PAM, and poorly for diazepam. Time to peak concentration approximated 2, 7, and 20 min for atropine, 2-PAM, and diazepam, respectively, and the elimination half-life of these drugs approximated 2 hr (atropine), 3 hr (2-PAM), and 8 hr (diazepam). Atropine sulfate dose-dependently increased the magnitude and duration of tachycardia and decreased the PR and ST intervals (consistent with findings obtained from other species). Mild hypothermia was observed at the highest diazepam dose. Göttingen minipigs appear to provide a ready and appropriate large animal alternative to non-human primates, and further development and evaluation of novel nerve agent medical countermeasures and treatment strategies in this model are justified.

Development and characterization of an automated behavioral assessment platform for the Göttingen minipig

The Göttingen minipig is fast becoming the standard for assessing dermal chemical hazards because, like most swine, its skin is predictive of human skin response and because this strain's smaller size makes laboratory manipulations and husbandry easier. Unfortunately, standard behavioral tests and apparatus have not been developed for behavioral assessments of this swine strain. Indeed, computer-controlled automated behavioral testing procedures are much needed. The present research advanced this goal by producing a home-cage behavioral testing system that could accommodate minipigs of various sizes (ages). An aluminum frame housed three levers for recording operant responses, and LEDs above and below each lever served as discriminative stimuli. A commercially available food pellet dispenser was attached to a specialized pellet receptacle capable of measuring pellet retrieval. Two behavioral tests were selected and adapted from our commonly used non-human primate behavioral assessments: delayed match-to-sample (a memory test) and temporal response differentiation (a time-estimation test). Minipigs were capable of learning both tests and attaining stable performance. Next, scopolamine was used to validate the sensitivity of the behavioral tests for gauging behavioral perturbations in this swine strain. Scopolamine dose-effect functions were comparable to those observed in other species, including non-human primates, wherein 37.5 µg/kg of scopolamine (administered intramuscularly) reduced responding approximately 50%. Thus, we were successful in developing the apparatus and automated operant behavioral tests necessary to characterize drug safety in this swine strain. This capability will be valuable for characterizing chemical agent toxicity as well as the safety and efficacy of medical countermeasures.

Carfentanil toxicity in the African green monkey: Therapeutic efficacy of naloxone

Carfentanil is an ultra-potent opioid with an analgesic potency 10,000 times that of morphine but has received little scientific investigation. Three experiments were conducted to evaluate the toxicity of carfentanil and the efficacy of naloxone in adult male African green monkeys. The first experiment determined the ED₅₀ (found to be 0.71 μg/kg) of subcutaneous carfentanil for inducing bradypnea and/or loss of posture. Experiment 2 attempted to establish the ED₅₀ of naloxone for rapidly reversing the bradypnea/loss of posture induced by carfentanil (1.15 μg/kg). Experiment 3 evaluated the effects of carfentanil (0.575 μg/kg) alone, the safety of naloxone (71-2841 μg/kg), and the efficacy of naloxone (71-710 μg/kg) administration at two time points following carfentanil (1.15 μg/kg) on operant choice reaction time. Collectively, these experiments characterized the temporal progression of carfentanil-induced toxic signs, determined the range of naloxone doses that restored respiratory and gross behavioral function, and determined the time course and range of naloxone doses that partially or completely reversed the effects of carfentanil on operant choice reaction time performance in African green monkeys. These results have practical relevance for the selection of opioid antagonists, initial doses, and expected functional outcomes following treatment of synthetic opioid overdose in a variety of operational/emergency response contexts.

Pharmacokinetics of K117 and K127, two novel antidote candidates to treat Tabun poisoning

AIMS

K117 and K127 are bis-pyridinium aldoximes but K117 is a bis-pyridinium bis-aldoxime while K127 has only one single aldoxime in addition to its amide substituent. Is there any difference in pharmacokinetics in these compounds that otherwise have the same chemical structure? Both K117 and K127 are developed as antidotes in acetylcholinesterase and butyrylcholinesterase poisoning in terrorist attacks or intoxication with other organophosphorous compounds. Their distributions have been scouted in the bodies of rats.

MAIN METHODS

White male Wistar rats were intramuscularly injected. The animals were sacrificed, tissue samples were homogenized, and either K117 or K127 concentrations were determined using reversed-phase high-performance liquid chromatography.

KEY FINDINGS

Both K117 and K127 were present in all tissues that were analyzed including blood (serum), the brains, cerebrospinal fluid, the eyes, livers, kidneys, lungs and testes. Their pharmacokinetics and body distributions are similar.

SIGNIFICANCE

Either K117 or K127 meets the essential requirements for antidotes. Dose dependence and kinetics of their distribution were compared to that of other pyridinium aldoximes.