Central Nervous System Antimicrobial Exposure and Proposed Dosing for Anthrax Meningitis.

BACKGROUND: The high mortality of systemic anthrax is likely a consequence of the severe central nervous system inflammation that occurs in anthrax meningitis. Effective treatment of such infections requires, at a minimum, adequate cerebrospinal fluid (CSF) antimicrobial concentrations. METHODS: We reviewed English medical literature and regulatory documents to extract information on serum and CSF exposures for antimicrobials with in vitro activity against Bacillus anthracis. Using CSF pharmacokinetic exposures and in vitro B. anthracis susceptibility data, we used population pharmacokinetic modeling and Monte Carlo simulations to determine whether a specific antimicrobial dosage would likely achieve effective CSF antimicrobial activity in patients with normal to inflamed meninges (ie, an intact to markedly disrupted blood-brain barrier). RESULTS: The probability of microbiologic success at achievable antimicrobial dosages was high (≥95%) for ciprofloxacin, levofloxacin (500 mg every 12 hours), meropenem, imipenem/cilastatin, penicillin G, ampicillin, ampicillin/sulbactam, doxycycline, and minocycline; acceptable (90%-95%) for piperacillin/tazobactam and levofloxacin (750 mg every 24 hours); and low (<90%) for vancomycin, amikacin, clindamycin, and linezolid. CONCLUSIONS: Prompt empiric antimicrobial therapy of patients with suspected or confirmed anthrax meningitis may reduce the high morbidity and mortality. Our data support using several ß-lactam-, fluoroquinolone-, and tetracycline-class antimicrobials as first-line and alternative agents for treatment of patients with anthrax meningitis; all should achieve effective microbiologic exposures. Our data suggest antimicrobials that should not be relied on to treat suspected or documented anthrax meningitis. Furthermore, the protein synthesis inhibitors clindamycin and linezolid can decrease toxin production and may be useful components of combination therapy.

Rapid in vitro activity of telavancin against Bacillus anthracis and in vivo protection against inhalation anthrax infection in the rabbit model.

Inhalation anthrax is the most severe form of Bacillus anthracis infection, often progressing to fatal conditions if left untreated. While recommended antibiotics can effectively treat anthrax when promptly administered, strains engineered for antibiotic resistance could render these drugs ineffective. Telavancin, a semisynthetic lipoglycopeptide antibiotic, was evaluated in this study as a novel therapeutic against anthrax disease. Specifically, the aims were to (i) assess in vitro potency of telavancin against 17 B. anthracis isolates by minimum inhibitory concentration (MIC) testing and (ii) evaluate protective efficacy in rabbits infected with a lethal dose of aerosolized anthrax spores and treated with human-equivalent intravenous telavancin doses (30 mg/kg every 12 hours) for 5 days post-antigen detection versus a humanized dose of levofloxacin and vehicle control. Blood samples were collected at various times post-infection to assess the level of bacteremia and antibody production, and tissues were collected to determine bacterial load. The animals' body temperatures were also recorded. Telavancin demonstrated potent bactericidal activity against all strains tested (MICs 0.06-0.125 µg/mL). Further, telavancin conveyed 100% survival in this model and cleared B. anthracis from the bloodstream and organ tissues more effectively than a humanized dose of levofloxacin. Collectively, the low MICs against all strains tested and rapid bactericidal in vivo activity demonstrate that telavancin has the potential to be an effective alternative for the treatment or prophylaxis of anthrax infection.

CDC Guidelines for the Prevention and Treatment of Anthrax, 2023.

This report updates previous CDC guidelines and recommendations on preferred prevention and treatment regimens regarding naturally occurring anthrax. Also provided are a wide range of alternative regimens to first-line antimicrobial drugs for use if patients have contraindications or intolerances or after a wide-area aerosol release of: Bacillus anthracis spores if resources become limited or a multidrug-resistant B. anthracis strain is used (Hendricks KA, Wright ME, Shadomy SV, et al.; Workgroup on Anthrax Clinical Guidelines. Centers for Disease Control and Prevention expert panel meetings on prevention and treatment of anthrax in adults. Emerg Infect Dis 2014;20:e130687; Meaney-Delman D, Rasmussen SA, Beigi RH, et al. Prophylaxis and treatment of anthrax in pregnant women. Obstet Gynecol 2013;122:885-900; Bradley JS, Peacock G, Krug SE, et al. Pediatric anthrax clinical management. Pediatrics 2014;133:e1411-36). Specifically, this report updates antimicrobial drug and antitoxin use for both postexposure prophylaxis (PEP) and treatment from these previous guidelines best practices and is based on systematic reviews of the literature regarding 1) in vitro antimicrobial drug activity against B. anthracis; 2) in vivo antimicrobial drug efficacy for PEP and treatment; 3) in vivo and human antitoxin efficacy for PEP, treatment, or both; and 4) human survival after antimicrobial drug PEP and treatment of localized anthrax, systemic anthrax, and anthrax meningitis. Changes from previous CDC guidelines and recommendations include an expanded list of alternative antimicrobial drugs to use when first-line antimicrobial drugs are contraindicated or not tolerated or after a bioterrorism event when first-line antimicrobial drugs are depleted or ineffective against a genetically engineered resistant: B. anthracis strain. In addition, these updated guidelines include new recommendations regarding special considerations for the diagnosis and treatment of anthrax meningitis, including comorbid, social, and clinical predictors of anthrax meningitis. The previously published CDC guidelines and recommendations described potentially beneficial critical care measures and clinical assessment tools and procedures for persons with anthrax, which have not changed and are not addressed in this update. In addition, no changes were made to the Advisory Committee on Immunization Practices recommendations for use of anthrax vaccine (Bower WA, Schiffer J, Atmar RL, et al. Use of anthrax vaccine in the United States: recommendations of the Advisory Committee on Immunization Practices, 2019. MMWR Recomm Rep 2019;68[No. RR-4]:1-14). The updated guidelines in this report can be used by health care providers to prevent and treat anthrax and guide emergency preparedness officials and planners as they develop and update plans for a wide-area aerosol release of B. anthracis.

Lysins as a powerful alternative to combat Bacillus anthracis.

This review gathers all, to the best of our current knowledge, known lysins, mainly bacteriophage-derived, that have demonstrated activity against Bacillus anthracis strains. B. anthracis is a spore-forming, toxin-producing bacteria, naturally dwelling in soil. It is best known as a potential biowarfare threat, an etiological agent of anthrax, and a severe zoonotic disease. Anthrax can be treated with antibiotics (ciprofloxacin, penicillin, doxycycline); however, their administration may take up even to 60 days, and different factors can compromise their effectiveness. Bacterial viruses, bacteriophages (phages), are natural enemies of bacteria and use their lytic enzymes, endolysins (lysins), to specifically kill bacterial cells. Harnessing the potential of lysins to combat bacterial infections holds promise for diminishing antibiotic usage and, consequently, addressing the escalating antibiotic resistance in bacteria. In this context, we list the lysins with the activity against B. anthracis, providing a summary of their lytic properties in vitro and the outcomes observed in animal models. Bacillus cereus strain ATCC 4342/RSVF1, a surrogate for B. anthracis, was also included as a target bacteria. KEY POINTS: • More than a dozen different B. anthracis lysins have been identified and studied. • They fall into three blocks regarding their amino acid sequence similarity and most of them are amidases. • Lysins could be used in treating B. anthracis infections.

Development of a Pharmacy Point-of-Dispensing Toolkit for Anthrax Post-Exposure Prophylaxis for Allegheny County Postal Workers.

CONTEXT: The Centers for Disease Control and Prevention (CDC) and the US Postal Service (USPS) consider anthrax to be a potential threat to USPS workers. A county health department-owned pharmacy supports local USPS response in the event of an exposure. The pharmacy team identified the need to review and update the local anthrax response plan. PROGRAM/POLICY: A Pharmacy Point-of-Dispensing Toolkit and response plan for initial 10-day post-exposure antibiotic prophylaxis was developed for use by a local health department in the event of a mass anthrax exposure at a US Post Office sorting facility. The pharmacist's role in medical countermeasures planning for anthrax exposure is also discussed to illustrate how pharmacists' medication expertise can be utilized. EVALUATION: The CDC's Public Health Preparedness Capabilities: National Standards for State and Local Planning framework and inputs from an interprofessional stakeholder team were used to develop a Medical Countermeasures Response Plan and Implementation Toolkit for mass point-of-dispensing (POD) in the event of an anthrax exposure. IMPLEMENTATION AND DISSEMINATION: Stakeholders attended a USPS Community Partner Training event where additional revisions to the toolkit were made. The toolkit and standing order are now implemented at the local health department to be reviewed and updated on a yearly basis by health department leadership. DISCUSSION: Pharmacists can use their medication expertise and experience with patient education to design emergency response plans focused on increasing patient safety and medication adherence. Pharmacists should be involved in emergency response and medical countermeasures planning that involve medications.

Efficacy of delafloxacin against the biothreat pathogen Bacillus anthracis.

OBJECTIVES: To evaluate the in vitro activity and in vivo efficacy of delafloxacin against Bacillus anthracis, the causative agent of anthrax. METHODS: MICs were obtained according to CLSI guidelines for 30 virulent isolates and 14 attenuated antibiotic-resistant strains. For the in vivo efficacy study, mice were administered delafloxacin (30-62.5 mg/kg) subcutaneously, or ciprofloxacin (30 mg/kg) intraperitoneally beginning at either 24 or 48 ±â€Š1 h post-challenge (post-exposure prophylaxis) and continued every 12 h for 14 days with study termination on day 30. The mean inhaled dose in the study was approximately 103 × LD50 equivalents, and the range was 87-120 × LD50. RESULTS: Delafloxacin (MIC90 = 0.004 mg/L) was 16-fold more potent than ciprofloxacin (MIC90 = 0.06 mg/L) against a 30-strain set of virulent B. anthracis. Against a panel of attenuated antibiotic-resistant strains, delafloxacin demonstrated potency ≥128-fold over that observed with ciprofloxacin. When evaluated in vivo, mice treated with all delafloxacin doses tested at 24 h post-challenge demonstrated equivalent survival compared with mice treated with the positive control ciprofloxacin. Because of the high challenge dose of spores, mice treated at 48 h showed rapid and high mortality in all groups including the positive control. Surviving animals in all delafloxacin- and ciprofloxacin-treated groups (24 and 48 h) showed complete splenic clearance of infection and <2.2 × 103 cfu/g lung tissue. CONCLUSIONS: Given the high bar set by the 100 × LD50 challenge dose in this study, the results from delafloxacin treatment are promising for the treatment of inhaled anthrax.

Pre- and Postlicensure Animal Efficacy Studies Comparing Anthrax Antitoxins.

BACKGROUND: The deliberate use of Bacillus anthracis spores is believed by the US government to be a high bioweapons threat. The first line of defense following potential exposure to B. anthracis spores would be postexposure prophylaxis with antimicrobials that have activity against B. anthracis. Additional therapies to address the effects of toxins may be needed in systemically ill individuals. Over the last 2 decades, the United States government (USG) collaborated with the private sector to develop, test, and stockpile 3 antitoxins: anthrax immunoglobulin intravenous (AIGIV), raxibacumab, and obiltoxaximab. All 3 products target protective antigen, a protein factor common to the 2 exotoxins released by B. anthracis, and hamper or block the toxins' effects and prevent or reduce pathogenesis. These antitoxins were approved for licensure by the United States Food and Drug Administration based on animal efficacy studies compared to placebo. METHODS: We describe USG-sponsored pre- and postlicensure studies that compared efficacy of 3 antitoxins in a New Zealand White rabbit model of inhalation anthrax; survival following a lethal aerosolized dose of B. anthracis spores was the key measure of effectiveness. To model therapeutic intervention, intravenous treatments were started following onset of antigenemia. RESULTS: In pre- and postlicensure studies, all 3 antitoxins were superior to placebo; in the postlicensure study, raxibacumab and obiltoxaximab were superior to AIGIV, but neither was superior to the other. CONCLUSIONS: These data illustrate the relative therapeutic benefit of the 3 antitoxins and provide a rationale to prioritize their deployment.

Safety of Antimicrobials for Postexposure Prophylaxis and Treatment of Anthrax: A Review.

BACKGROUND: Bacillus anthracis, the causative agent for anthrax, poses a potential bioterrorism threat and is capable of causing mass morbidity and mortality. Antimicrobials are the mainstay of postexposure prophylaxis (PEP) and treatment of anthrax. We conducted this safety review of 24 select antimicrobials to identify any new or emerging serious or severe adverse events (AEs) to help inform their risk-benefit evaluation for anthrax. METHODS: Twenty-four antimicrobials were included in this review. Tertiary data sources (e.g. Lactmed, Micromedex, REPROTOX) were reviewed for safety information and summarized to evaluate the known risks of these antimicrobials. PubMed was also searched for published safety information on serious or severe AEs with these antimicrobials; AEs that met inclusion criteria were abstracted and reviewed. RESULTS: A total of 1316 articles were reviewed. No consistent observations or patterns were observed among the abstracted AEs for a given antimicrobial; therefore, the literature review did not reveal evidence of new or emerging AEs that would add to the risk-benefit profiles already known from tertiary data sources. CONCLUSIONS: The reviewed antimicrobials have known and/or potential serious or severe risks that may influence selection when recommending an antimicrobial for PEP or treatment of anthrax. Given the high fatality rate of anthrax, the risk-benefit evaluation favors use of these antimicrobials for anthrax. The potential risks of antimicrobials should not preclude these reviewed antimicrobials from clinical consideration for anthrax but rather guide appropriate antimicrobial selection and prioritization across different patient populations with risk mitigation measures as warranted.

Survival of Patient With Hemorrhagic Meningitis Associated With Inhalation Anthrax.

This report describes a 49-year-old male construction worker who acquired a Bacillus anthracis infection after working on a sheep farm. He experienced a severe respiratory infection, septic shock, and hemorrhagic meningoencephalitis with severe intracranial hypertension. After several weeks with multiple organ dysfunction syndrome, he responded favorably to antibiotic treatment. Three weeks into his hospitalization, an intracranial hemorrhage and cerebral edema led to an abrupt deterioration in his neurological status. A single dose of raxibacumab was added to his antimicrobial regimen on hospital day 27. His overall status, both clinical and radiographic, improved within a few days. He was discharged 2 months after admission and appears to have fully recovered.

Antitoxin Use in the Prevention and Treatment of Anthrax Disease: A Systematic Review.

BACKGROUND: Bacillus anthracis is a high-priority threat agent because of its widespread availability, easy dissemination, and ability to cause substantial morbidity and mortality. Although timely and appropriate antimicrobial therapy can reduce morbidity and mortality, the role of adjunctive therapies continues to be explored. METHODS: We searched 11 databases for articles that report use of anthrax antitoxins in treatment or prevention of systemic anthrax disease published through July 2019. We identified other data sources through reference search and communication with experts. We included English-language studies on antitoxin products with approval by the US Food and Drug Administration (FDA) for anthrax in humans, nonhuman primates, and rabbits. Two researchers independently reviewed studies for inclusion and abstracted relevant data. RESULTS: We abstracted data from 12 publications and 2 case reports. All 3 FDA-approved anthrax antitoxins demonstrated significant improvement in survival as monotherapy over placebo in rabbits and nonhuman primates. No study found significant improvement in survival with combination antitoxin and antimicrobial therapy compared to antimicrobial monotherapy. Case reports and case series described 25 patients with systemic anthrax disease treated with antitoxins; 17 survived. Animal studies that used antitoxin monotherapy as postexposure prophylaxis (PEP) demonstrated significant improvement in survival over placebo, with greatest improvements coming with early administration. CONCLUSIONS: Limited human and animal evidence indicates that adjunctive antitoxin treatment may improve survival from systemic anthrax infection. Antitoxins may also provide an alternative therapy to antimicrobials for treatment or PEP during an intentional anthrax incident that could involve a multidrug-resistant B. anthracis strain.

Welder's Anthrax: A Tale of 2 Cases.

Bacillus anthracis has traditionally been considered the etiologic agent of anthrax. However, anthrax-like illness has been documented in welders and other metal workers infected with Bacillus cereus group spp. harboring pXO1 virulence genes that produce anthrax toxins. We present 2 recent cases of severe pneumonia in welders with B. cereus group infections and discuss potential risk factors for infection and treatment options, including antitoxin.

Determination of the Postexposure Prophylactic Benefit of Oral Azithromycin and Clarithromycin Against Inhalation Anthrax in Cynomolgus Macaques.

BACKGROUND: Sufficient and diverse medical countermeasures against severe pathogenic infections, such as inhalation anthrax, are a critical need. Azithromycin and clarithromycin are antimicrobials commonly used for both upper and lower respiratory infections. They inhibit protein synthesis by blocking the formation of the 50S ribosomal subunit. To expand the armamentarium, these 2 antibiotics were evaluated in a postexposure prophylactic model of inhalation anthrax in cynomolgus macaques. METHODS: This prophylaxis study had 4 test arms: azithromycin, clarithromycin, a levofloxacin control, and a placebo. Beginning 24 hours after exposure to a target challenge dose of 200 lethal dose 50 (LD50) of Bacillus anthracis Ames spores, animals were treated orally until 30 days postchallenge and then observed until 75 days postchallenge. RESULTS: The test group that received clarithromycin had a survival rate of 67%. The test group that received azithromycin had a survival rate of 50%, but the peak azithromycin plasma levels achieved were <30 ng/mL-much lower than the expected 410 ng/mL. The levofloxacin positive control had a survival rate of 50%; all of the negative controls succumbed to infection. CONCLUSIONS: The efficacy of clarithromycin prophylaxis was statistically significant compared with placebo, while azithromycin prophylaxis was indistinguishable from placebo. Given the low plasma concentrations of azithromycin achieved in the study, it is not surprising that half the animals succumbed to anthrax during the dosing period; the animals that survived beyond the time during which placebo control animals succumbed survived to the end of the observation period.

Systematic Review of Hospital Treatment Outcomes for Naturally Acquired and Bioterrorism-Related Anthrax, 1880-2018.

BACKGROUND: Bacillus anthracis can cause anthrax and is a potential bioterrorism agent. The 2014 Centers for Disease Control and Prevention recommendations for medical countermeasures against anthrax were based on in vitro data and expert opinion. However, a century of previously uncompiled observational human data that often includes treatment and outcomes is available in the literature for analysis. METHODS: We reviewed treatment outcomes for patients hospitalized with anthrax. We stratified patients by meningitis status, route of infection, and systemic criteria, then analyzed survival by treatment type, including antimicrobials, antitoxin/antiserum, and steroids. Using logistic regression, we calculated odds ratios and 95% confidence intervals to compare survival between treatments. We also calculated hospital length of stay. Finally, we evaluated antimicrobial postexposure prophylaxis (PEPAbx) using data from a 1970 Russian-language article. RESULTS: We identified 965 anthrax patients reported from 1880 through 2018. After exclusions, 605 remained: 430 adults, 145 children, and 30 missing age. Survival was low for untreated patients and meningitis patients, regardless of treatment. Most patients with localized cutaneous or nonmeningitis systemic anthrax survived with 1 or more antimicrobials; patients with inhalation anthrax without meningitis fared better with at least 2. Bactericidal antimicrobials were effective for systemic anthrax; addition of a protein synthesis inhibitor(s) (PSI) to a bactericidal antimicrobial(s) did not improve survival. Likewise, addition of antitoxin/antiserum to antimicrobials did not improve survival. Mannitol improved survival for meningitis patients, but steroids did not. PEPAbx reduced risk of anthrax following exposure to B. anthracis. CONCLUSIONS: Combination therapy appeared to be superior to monotherapy for inhalation anthrax without meningitis. For anthrax meningitis, neither monotherapy nor combination therapy were particularly effective; however, numbers were small. For localized cutaneous anthrax, monotherapy was sufficient. For B. anthracis exposures, PEPAbx was effective.

Anthrax Meningoencephalitis and Intracranial Hemorrhage.

The neurological sequelae of Bacillus anthracis infection include a rapidly progressive fulminant meningoencephalitis frequently associated with intracranial hemorrhage, including subarachnoid and intracerebral hemorrhage. Higher mortality than other forms of bacterial meningitis suggests that antimicrobials and cardiopulmonary support alone may be insufficient and that strategies targeting the hemorrhage might improve outcomes. In this review, we describe the toxic role of intracranial hemorrhage in anthrax meningoencephalitis. We first examine the high incidence of intracranial hemorrhage in patients with anthrax meningoencephalitis. We then review common diseases that present with intracranial hemorrhage, including aneurysmal subarachnoid hemorrhage and spontaneous intracerebral hemorrhage, postulating applicability of established and potential neurointensive treatments to the multimodal management of hemorrhagic anthrax meningoencephalitis. Finally, we examine the therapeutic potential of minocycline, an antimicrobial that is effective against B. anthracis and that has been shown in preclinical studies to have neuroprotective properties, which thus might be repurposed for this historically fatal disease.

Risk Factors for Severe Cutaneous Anthrax in a Retrospective Case Series and Use of a Clinical Algorithm to Identify Likely Meningitis and Evaluate Treatment Outcomes, Kyrgyz Republic, 2005-2012.

BACKGROUND: US Centers for Disease Control and Prevention guidelines currently recommend triple-therapy antimicrobial treatment for anthrax meningitis. In the Kyrgyz Republic, a country with endemic anthrax, cutaneous anthrax patients are routinely hospitalized and treated successfully with only monotherapy or dual therapy. Clinical algorithms have been developed to identify patients with likely anthrax meningitis based on signs and symptoms alone. We sought to retrospectively identify likely meningitis patients in the Kyrgyz Republic using a clinical algorithm and evaluate risk factors and their outcomes by type of treatment. METHODS: We conducted a retrospective chart review of cutaneous anthrax patients in the Kyrgyz Republic from 2005 through 2012. Using previous methods, we developed a highly specific algorithm to categorize patients by meningitis status. We then evaluated patient risk factors, treatments, and outcomes by disease severity and meningitis status. RESULTS: We categorized 37 of 230 cutaneous anthrax patients as likely having meningitis. All 37 likely meningitis patients survived, receiving only mono- or dual-therapy antimicrobials. We identified underlying medical conditions, such as obesity, hypertension, and chronic obstructive pulmonary disease, and tobacco and alcohol use, as potential risk factors for severe anthrax and anthrax meningitis. CONCLUSIONS: Based on our analyses, treatment of anthrax meningitis may not require 3 antimicrobials, which could impact future anthrax treatment recommendations. In addition, chronic comorbidities may increase risk for severe anthrax and anthrax meningitis. Future research should further investigate potential risk factors for severe anthrax and their impact on laboratory-confirmed meningitis and evaluate mono- and dual-therapy antimicrobial regimens for anthrax meningitis.

Postexposure Prophylaxis and Treatment of Bacillus anthracis Infections: A Systematic Review and Meta-analyses of Animal Models, 1947-2019.

BACKGROUND: Anthrax is endemic to many countries, including the United States. The causative agent, Bacillus anthracis, poses a global bioterrorism threat. Without effective antimicrobial postexposure prophylaxis (PEPAbx) and treatment, the mortality of systemic anthrax is high. To inform clinical guidelines for PEPAbx and treatment of B. anthracis infections in humans, we systematically evaluated animal anthrax treatment model studies. METHODS: We searched for survival outcome data in 9 scientific search engines for articles describing antimicrobial PEPAbx or treatment of anthrax in animals in any language through February 2019. We performed meta-analyses of efficacy of antimicrobial PEPAbx and treatment for each drug or drug combination using random-effects models. Pharmacokinetic/pharmacodynamic relationships were developed for 5 antimicrobials with available pharmacokinetic data. Monte Carlo simulations were used to predict unbound drug exposures in humans. RESULTS: We synthesized data from 34 peer-reviewed studies with 3262 animals. For PEPAbx and treatment of infection by susceptible B. anthracis, effective monotherapy can be accomplished with fluoroquinolones, tetracyclines, ß-lactams (including penicillin, amoxicillin-clavulanate, and imipenem-cilastatin), and lipopeptides or glycopeptides. For naturally occurring strains, unbound drug exposures in humans were predicted to adequately cover the minimal inhibitory concentrations (MICs; those required to inhibit the growth of 50% or 90% of organisms [MIC50 or MIC90]) for ciprofloxacin, levofloxacin, and doxycycline for both the PEPAbx and treatment targets. Dalbavancin covered its MIC50 for PEPAbx. CONCLUSIONS: These animal studies show many reviewed antimicrobials are good choices for PEPAbx or treatment of susceptible B. anthracis strains, and some are also promising options for combating resistant strains. Monte Carlo simulations suggest that oral ciprofloxacin, levofloxacin, and doxycycline are particularly robust choices for PEPAbx or treatment.

Anthrax toxin component, Protective Antigen, protects insects from bacterial infections.

Anthrax is a major zoonotic disease of wildlife, and in places like West Africa, it can be caused by Bacillus anthracis in arid nonsylvatic savannahs, and by B. cereus biovar anthracis (Bcbva) in sylvatic rainforests. Bcbva-caused anthrax has been implicated in as much as 38% of mortality in rainforest ecosystems, where insects can enhance the transmission of anthrax-causing bacteria. While anthrax is well-characterized in mammals, its transmission by insects points to an unidentified anthrax-resistance mechanism in its vectors. In mammals, a secreted anthrax toxin component, 83 kDa Protective Antigen (PA83), binds to cell-surface receptors and is cleaved by furin into an evolutionary-conserved PA20 and a pore-forming PA63 subunits. We show that PA20 increases the resistance of Drosophila flies and Culex mosquitoes to bacterial challenges, without directly affecting the bacterial growth. We further show that the PA83 loop known to be cleaved by furin to release PA20 from PA63 is, in part, responsible for the PA20-mediated protection. We found that PA20 binds directly to the Toll activating peptidoglycan-recognition protein-SA (PGRP-SA) and that the Toll/NF-κB pathway is necessary for the PA20-mediated protection of infected flies. This effect of PA20 on innate immunity may also exist in mammals: we show that PA20 binds to human PGRP-SA ortholog. Moreover, the constitutive activity of Imd/NF-κB pathway in MAPKK Dsor1 mutant flies is sufficient to confer the protection from bacterial infections in a manner that is independent of PA20 treatment. Lastly, Clostridium septicum alpha toxin protects flies from anthrax-causing bacteria, showing that other pathogens may help insects resist anthrax. The mechanism of anthrax resistance in insects has direct implications on insect-mediated anthrax transmission for wildlife management, and with potential for applications, such as reducing the sensitivity of pollinating insects to bacterial pathogens.

'A remedy for this dread disease': Achille Sclavo, anthrax and serum therapy in early twentieth-century Britain.

In the years around 1900 one of the most significant practical consequences of new styles of bacteriological thought and practice was the development of preventive vaccines and therapeutic sera. Historical scholarship has highlighted how approaches rooted in the laboratory methods of Robert Koch, Louis Pasteur and their collaborators were transformed in local contexts and applied in diverse ways to enable more effective disease identification, prevention and treatment. Amongst these, the anti-anthrax serum developed by the Italian physician Achille Sclavo (1861-1930) has received little to no attention from historians. This article positions Sclavo's serum as a neglected but significant presence in British microbiology, which achieved widespread uptake amidst a wave of optimism, despite prolonged uncertainty about its mechanism of action and dosage. After being introduced to Britain in 1904 by the enterprising first medical inspector of factories Thomas Morison Legge, within a matter of months the serum became regarded by medical practitioners as an effective treatment of cutaneous anthrax, though access to 'fresh' serum and the necessary speedy diagnosis remained problematic. Like the disease anthrax itself, discussion of 'Sclavo's serum' was out of all proportion to the relatively low number of cases, reflecting a deep-seated fascination with the wider possibilities afforded by effective serum therapy.

Population pharmacokinetics of raxibacumab in healthy adult subjects.

AIMS: Raxibacumab is a fully humanized monoclonal antibody that blocks the interaction of Bacillus anthracis toxins, thereby protecting target cells from its effects. Raxibacumab is approved in the USA for the treatment of adults and children with inhalational anthrax in combination with antibiotics, and for prophylaxis of inhalational anthrax. The aim of this investigation was to characterise the population pharmacokinetics and assess the effect of baseline demographic covariates on the disposition of raxibacumab. METHODS: The data used for this analysis were obtained from 3 clinical trials and include 2229 blood samples from 322 healthy subjects who were randomised to receive a 40 mg/kg intravenous dose of raxibacumab over a period of 2.25 hours. Population pharmacokinetic modelling was performed using a nonlinear mixed effects approach. Secondary parameters of interest were the area under the curve, maximum concentration and the time of serum raxibacumab concentrations greater than or equimolar to the highest serum protective antigen concentrations observed for at least 28 days in any monkey challenged with B. anthracis that died. RESULTS: Raxibacumab exposure in healthy subjects was described by a 2-compartment model. Interindividual variability was estimated for all model parameters, whilst residual variability was described by a proportional and additive error model. Weight was the only influential covariate with significant effect on disposition parameters. CONCLUSIONS: A dose of 40 mg/kg provided comparable exposure across the overall healthy subject population. Interindividual variability in raxibacumab vs. time profiles could partially be accounted for by differences in body weight.

Extrapolation and dosing recommendations for raxibacumab in children from birth to age <18 years.

AIMS: The US Food and Drug Administration's Animal Rule allows for the approval of drugs when human efficacy studies are not ethical. While the therapeutic doses of raxibacumab, a monoclonal antibody for the prophylaxis and treatment of inhalational anthrax, have been based on pharmacokinetic data from adult subjects, its disposition in children has not been investigated in clinical trials. Here we evaluate the effect of demographic covariates and maturation processes on the pharmacokinetics of raxibacumab and explore opportunities for the optimisation of paediatric doses. METHODS: A population pharmacokinetic model was used as basis for the extrapolation of raxibacumab disposition from adults to children. Different extrapolation scenarios, including weight-banded dosing regimens, were considered to assess the effect of growth and maturation on the pharmacokinetic parameters of interest. Area under the concentration-time curve, maximum plasma concentration and the time of serum raxibacumab concentrations greater than or equimolar to the highest serum protective antigen concentrations observed for at least 28 days in any monkey challenged with Bacillus anthracis that died were derived and compared with the currently approved US doses. RESULTS: Based on practical considerations, a weight-banded dosing regimen consisting of 4 dose levels (75 mg/kg for individuals ≤1.5 kg, 55 mg/kg for individuals <10 kg, 45 mg/kg for individuals <50 kg, 40 mg/kg for all individuals >50 kg) was required to optimise target exposure across the paediatric population. CONCLUSIONS: Age-related maturation processes may affect raxibacumab clearance in very young patients. The proposed dosing regimens take into account effects of body weight and maturation processes on the elimination of raxibacumab.