Efficacy of high dose tranexamic acid (TXA) for hemorrhage: A systematic review and meta-analysis.

BACKGROUND: Standard dose (≤ 1 g) tranexamic acid (TXA) has established mortality benefit in trauma patients. The role of high dose IV TXA (≥2 g or ≥30 mg/kg as a single bolus) has been evaluated in the surgical setting, however, it has not been studied in trauma. We reviewed the available evidence of high dose IV TXA in any setting with the goal of informing its use in the adult trauma population. METHODS: We searched MEDLINE, EMBASE and unpublished sources from inception until July 27, 2022 for studies that compared standard dose with high dose IV TXA in adults (≥ 16 years of age) with hemorrhage. Screening and data abstraction was done independently and in duplicate. We pooled trial data using a random effects model and considered randomized controlled trials (RCTs) and observational cohort studies separately. We assessed the individual study risk of bias using the Cochrane Risk of Bias for RCTs and the Newcastle-Ottawa Scale for observational cohort studies. The overall certainty of evidence was assessed using the GRADE approach (Grading of Recommendations Assessment, Development and Evaluation). RESULTS: We included 20 studies with a combined total of 12,523 patients. Based on pooled RCT data, and as compared to standard dose TXA, high dose IV TXA probably decreases transfusion requirements (odds ratio [OR] 0.86, 95% confidence interval [CI] 0.76 to 0.97, moderate certainty) but with possibly no effect on blood loss (mean difference [MD] 43.31 ml less, 95% CI 135.53 to 48.90 ml less, low certainty), and an uncertain effect on thromboembolic events (OR 1.33, 95% CI 0.86 to 2.04, very low certainty) and mortality (OR 0.70, 95% CI 0.37 to 1.32, very low certainty). CONCLUSION: When compared to standard dose, high dose IV TXA probably reduces transfusion requirements with an uncertain effect on thromboembolic events and mortality. LEVEL OF EVIDENCE: Systematic review and meta-analysis, level IV.

Pharmacokinetics and efficacy of atropine sulfate/obidoxime chloride co-formulation against VX in a guinea pig model.

Nerve agent exposure is generally treated by an antidote formulation composed of a muscarinic antagonist, atropine sulfate (ATR), and a reactivator of acetylcholinesterase (AChE) such as pralidoxime, obidoxime (OBI), methoxime, trimedoxime or HI-6 and an anticonvulsant. Organophosphates (OPs) irreversibly inhibit AChE, the enzyme responsible for termination of acetylcholine signal transduction. Inhibition of AChE leads to overstimulation of the central and peripheral nervous system with convulsive seizures, respiratory distress and death as result. The present study evaluated the efficacy and pharmacokinetics (PK) of ATR/OBI following exposure to two different VX dose levels. The PK of ATR and OBI administered either as a single drug, combined treatment but separately injected, or administered as the ATR/OBI co-formulation, was determined in plasma of naïve guinea pigs and found to be similar for all formulations. Following subcutaneous VX exposure, ATR/OBI-treated animals showed significant improvement in survival rate and progression of clinical signs compared to untreated animals. Moreover, AChE activity after VX exposure in both blood and brain tissue was significantly higher in ATR/OBI-treated animals compared to vehicle-treated control. In conclusion, ATR/OBI has been proven to be efficacious against exposure to VX and there were no PK interactions between ATR and OBI when administered as a co-formulation.

Cerebral blood flow and oxygenation in rat brain after soman exposure.

Nerve agent exposure can cause debilitating neurological damage even with treatment. Currently accepted treatments involve attenuating the cholinergic crisis and seizure onset but do not focus directly on neuroprotection. Hence, there is a need for improved treatments to reduce neurological deficits. It is important to understand the pathophysiology of nerve agent mediated injury in order to identify effective treatment targets. Nerve agent-induced seizures are believed to be the main contributor to the neuropathology. Recently seizures have been shown to cause vascular changes that may actually attenuate neurological damage. This study evaluated the effect of soman-induced convulsive seizures on the relationship between CNS oxygen consumption and supply. To simultaneously assess changes in oxygenation and perfusion, rats were implanted with permanently fixed fiber-optic tissue oxygen sensing probes in the motor cortex and imaged with continuous arterial spin labelling MRI to measure cerebral blood flow. Baseline tissue oxygen tension (ptO2) and cerebral blood flow (CBF) were measured in isoflurane anaesthetized rats at least one day prior to soman or saline exposure. Rats were pretreated with HI-6 dimethansulfonate and atropine methyl nitrate (125 mg/kg and 20 mg/kg; intraperitoneal) followed by a convulsive dose of soman (90 µg/kg; subcutaneous) or equal volume of saline. Three additional treatments of HI-6/AMN were administered to improve survival. At 1.5 -hs after exposure, ptO2 and cerebral blood flow measurements were conducted. There was a significant decrease in CBF 1.5 -hs following soman exposure but no change in ptO2 was found. When we correlated ptO2 and CBF, for a given ptO2, there was lower CBF following soman exposure. This may indicate metabolism is inhibited, possibly because of mitochondrial impairment, therefore reducing oxygen demand. These data show hypoperfusion in brain following soman exposure which would be expected to contribute to soman-related neuropathology.

Quantitative T2 MRI is predictive of neurodegeneration following organophosphate exposure in a rat model.

Organophosphorus compounds, such as chemical warfare nerve agents and pesticides, are known to cause neurological damage. This study measured nerve agent-related neuropathology and determined whether quantitative T2 MRI could be used as a biomarker of neurodegeneration. Quantitative T2 MRI was performed using a 9.4 T MRI on rats prior to and following soman exposure. T2 images were taken at least 24 h prior, 1 h and 18-24 h after soman exposure. Rats were pre- and post-treated with HI-6 dimethanesulfonate and atropine methyl nitrate. A multicomponent T2 acquisition and analysis was performed. Brains were stained with Fluoro-Jade C to assess neurodegeneration. Rats exposed to soman developed behavioral expression of electrographic seizures. At 18-24 h after soman exposure, significant increases in T2, a possible marker of edema, were found in multiple regions. The largest changes were in the piriform cortex (before: 47.7 ± 1.4 ms; 18-24 h: 82.3 ± 13.4 ms). Fluoro-Jade C staining showed significant neurodegeneration 18-24 h post exposure. The piriform cortex had the strongest correlation between the change in relaxation rate and percent neurodegeneration (r = 0.96, p < 0.001). These findings indicate there is regionally specific neurodegeneration 24 h after exposure to soman. The high correlation between T2 relaxivity and histopathology supports the use of T2 as a marker of injury.

Comparative physiology and efficacy of atropine and scopolamine in sarin nerve agent poisoning.

Anticholinergic treatment is key for effective medical treatment of nerve agent exposure. Atropine is included at a 2 mg intramuscular dose in so-called autoinjectors designed for self- and buddy-aid. As patient cohorts are not available, predicting and evaluating the efficacy of medical countermeasures relies on animal models. The use of atropine as a muscarinic antagonist is based on efficacy achieved in studies in a variety of species. The dose of atropine administered varies considerably across these studies. This is a complicating factor in the prediction of efficacy in the human situation, largely because atropine dosing also influences therapeutic efficacy of oximes and anticonvulsants generally part of the treatment administered. To improve translation of efficacy of dosing regimens, including pharmacokinetics and physiology provide a promising approach. In the current study, pharmacokinetics and physiological parameters obtained using EEG and ECG were assessed in naïve rats and in sarin-exposed rats for two anticholinergic drugs, atropine and scopolamine. The aim was to find a predictive parameter for therapeutic efficacy. Scopolamine and atropine showed a similar bioavailability, but brain levels reached were much higher for scopolamine. Scopolamine exhibited a dose-dependent loss of beta power in naïve animals, whereas atropine did not show any such central effect. This effect was correlated with an enhanced anticonvulsant effect of scopolamine compared to atropine. These findings show that an approach including pharmacokinetics and physiology could contribute to improved dose scaling across species and assessing the therapeutic potential of similar anticholinergic and anticonvulsant drugs against nerve agent poisoning.

Pharmacokinetics of Three Oximes in a Guinea Pig Model and Efficacy of Combined Oxime Therapy.

Organophosphorus nerve agents (NA) inhibit acetylcholinesterase (AChE) which results in the over-stimulation of both the central and peripheral nervous systems, creating a toxic syndrome that can be lethal if left untreated (Cannard, 2006). It is standard practice to treat Sarin (GB) intoxication with an oxime, an antimuscarinic such as atropine and an anticonvulsant. Three common oximes are available: HI-6, Pralidoxime (2-PAM) and Obidoxime (Obi), all possess a nucleophile that can break the NA-AChE covalent bond. However, each oxime's efficacy profile against various agents is different (Thiermann and Worek, 2018). In an effort to broaden therapeutic efficacy against a range of possible NA's, consideration should be given to the use of two oximes in combination. Using a guinea pig model, the first arm of this study was to determine the pharmacokinetics (PK) of HI-6 DMS, 2-PAM chloride and Obi chloride (at autoinjector equivalent doses) following intramuscular (i.m.) co-administration along with atropine to replicate either a single isometrically scaled dose (referred to in this study as a single autoinjector equivalent) of 2-PAM (and equimolar doses of Obi and HI-6) or double doses (referred to in this study as two autoinjector equivalents). The second arm of the study evaluated the efficacy of Obi and 2-PAM individually at a single or double autoinjector dose and also in combination against GB exposure. Pharmacokinetic profiles of each oxime were evaluated for both arms of the study and no significant change in parameters were reported. Improved cholinesterase reactivation was observed in a dose dependent manner with combined therapy showing similar reactivation to individual oximes alone at a two autoinjector equivalent dose. Seizure activity was reduced when combined oxime therapy was administered. This improvement was also reflected in the Racine seizure index score assigned at the end of the experimental period. To the best of our knowledge, this study is the first to evaluate and compare the pharmacokinetics of three oximes and the combination of two oximes (2-PAM and Obi) administered in naïve animals or those exposed to GB. Combined oxime therapy (Obi and 2-PAM) resulted in improved seizure control, increased cholinesterase reactivation peripherally and centrally and improved behavioral signs (Racine score). This study provides evidence that combination of oximes is effective, does not result in adverse events and that the pharmacokinetics of each oxime are not affected when administered in combination.

Assessment of brain oxygenation imbalance following soman exposure in rats.

Nerve agents (NAs) are potent organophosphorus (OP) compounds with applications in chemical warfare. OP compounds act by inhibiting acetylcholinesterase (AChE). Soman (O-pinacolyl methylphosphonofluoridate) is one of the most potent NAs. It is well known that small doses of NAs can be lethal, and that even non-lethal exposure leads to long-term mental debilitation/neurological damage. However, the neuropathology following exposure to sub-lethal nerve agents is not well understood. In this study, we examined changes in tissue oxygenation (pO2) in the cortex and hippocampus after a sub-lethal dose of soman [80-90 µg/kg; subcutaneous]. pO2 changes can provide information regarding oxygen delivery and utilization and may be indicative of a disruption in cerebral blood flow and/or metabolism. Changes in oxygenation were measured with chronically implanted oxygen sensors in awake and freely moving rats. Measurements were taken before, during, and after soman-induced convulsive seizures. Soman exposure resulted in an immediate increase in pO2 in the cortex, followed by an even greater increase that precedes the onset of soman-induced convulsive seizures. The rise in hippocampus pO2 was delayed relative to the cortex, although the general pattern of brain oxygenation between these two regions was similar. After convulsive seizures began, pO2 levels declined but usually remained hyperoxygenated. Following the decline in pO2, low frequency cycles of large amplitude changes were observed in both the cortex and hippocampus. This pattern is consistent with recurring seizures. Measuring real-time changes in brain pO2 provides new information on the physiological status of the brain following soman exposure. These results highlight that the measurement of brain oxygenation could provide a sensitive marker of nerve agent exposure and serve as a biomarker for treatment studies.

Development and validation of a sensitive HPLC method for the quantification of HI-6 in guinea pig plasma and evaluated in domestic swine.

A rapid and small volume assay to quantify HI-6 in plasma was developed to further the development and licensing of an intravenous formulation of HI-6. The objective of this method was to develop a sensitive and rapid assay that clearly resolved HI-6 and an internal standard in saline and plasma matrices. A fully validated method using ion-pair HPLC and 2-PAM as the internal standard fulfilled these requirements. Small plasma samples of 35 microL were extracted using acidification, filtration and neutralization. Linearity was shown for over 4 microg/mL to 1mg/mL with accuracy and precision within 6% relative error at the lower limit of detection. This method was utilized in the pharmacokinetic analysis HI-6 dichloride (2Cl) and HI-6 dimethane sulfonate (DMS) in anaesthetized guinea pigs and domestic swine following an intravenous bolus administration. From the resultant pharmacokinetic parameters a target plasma concentration of 100 microM was established and maintained in guinea pigs receiving an intravenous infusion. This validated method allows for the analysis of low volume samples, increased sample numbers and is applicable to the determination of pharmacokinetic profiles and parameters.