Molecular pharmacodynamics of meropenem for nosocomial pneumonia caused by Pseudomonas aeruginosa.

Hospital-acquired pneumonia (HAP) is a leading cause of morbidity and mortality, commonly caused by Pseudomonas aeruginosa. Meropenem is a commonly used therapeutic agent, although emergent resistance occurs during treatment. We used a rabbit HAP infection model to assess the bacterial kill and resistance pharmacodynamics of meropenem. Meropenem 5 mg/kg administered subcutaneously (s.c.) q8h (±amikacin 3.33-5 mg/kg q8h administered intravenously[i.v.]) or meropenem 30 mg/kg s.c. q8h regimens were assessed in a rabbit lung infection model infected with P. aeruginosa, with bacterial quantification and phenotypic/genotypic characterization of emergent resistant isolates. The pharmacokinetic/pharmacodynamic output was fitted to a mathematical model, and human-like regimens were simulated to predict outcomes in a clinical context. Increasing meropenem monotherapy demonstrated a dose-response effect to bacterial kill and an inverted U relationship with emergent resistance. The addition of amikacin to meropenem suppressed the emergence of resistance. A network of porin loss, efflux upregulation, and increased expression of AmpC was identified as the mechanism of this emergent resistance. A bridging simulation using human pharmacokinetics identified meropenem 2 g i.v. q8h as the licensed clinical regimen most likely to suppress resistance. We demonstrate an innovative experimental platform to phenotypically and genotypically characterize bacterial emergent resistance pharmacodynamics in HAP. For meropenem, we have demonstrated the risk of resistance emergence during therapy and identified two mitigating strategies: (i) regimen intensification and (ii) use of combination therapy. This platform will allow pre-clinical assessment of emergent resistance risk during treatment of HAP for other antimicrobials, to allow construction of clinical regimens that mitigate this risk.IMPORTANCEThe emergence of antimicrobial resistance (AMR) during antimicrobial treatment for hospital-acquired pneumonia (HAP) is a well-documented problem (particularly in pneumonia caused by Pseudomonas aeruginosa) that contributes to the wider global antimicrobial resistance crisis. During drug development, regimens are typically determined by their sufficiency to achieve bactericidal effect. Prevention of the emergence of resistance pharmacodynamics is usually not characterized or used to determine the regimen. The innovative experimental platform described here allows characterization of the emergence of AMR during the treatment of HAP and the development of strategies to mitigate this. We have demonstrated this specifically for meropenem-a broad-spectrum antibiotic commonly used to treat HAP. We have characterized the antimicrobial resistance pharmacodynamics of meropenem when used to treat HAP, caused by initially meropenem-susceptible P. aeruginosa, phenotypically and genotypically. We have also shown that intensifying the regimen and using combination therapy are both strategies that can both treat HAP and suppress the emergence of resistance.

Development and application of neonatal physiology-based pharmacokinetic models of amikacin and fosfomycin to assess pharmacodynamic target attainment.

Antimicrobial resistance increasingly complicates neonatal sepsis in a global context. Fosfomycin and amikacin are two agents being tested in an ongoing multicenter neonatal sepsis trial. Although neonatal pharmacokinetics (PKs) have been described for these drugs, the physiological variability within neonatal populations makes population PKs in this group uncertain. Physiologically-based pharmacokinetic (PBPK) models were developed in Simcyp for fosfomycin and amikacin sequentially for adult, pediatric, and neonatal populations, with visual and quantitative validation compared to observed data at each stage. Simulations were performed using the final validated neonatal models to determine drug exposures for each drug across a demographic range, with probability of target attainment (PTA) assessments. Successfully validated neonatal PBPK models were developed for both fosfomycin and amikacin. PTA analysis demonstrated high probability of target attainment for amikacin 15 mg/kg i.v. q24h and fosfomycin 100 mg/kg (in neonates aged 0-7 days) or 150 mg/kg (in neonates aged 7-28 days) i.v. q12h for Enterobacterales with fosfomycin and amikacin minimum inhibitory concentrations at the adult breakpoints. Repeat analysis in premature populations demonstrated the same result. PTA analysis for a proposed combination fosfomycin-amikacin target was also performed. The simulated regimens, tested in a neonatal sepsis trial, are likely to be adequate for neonates across different postnatal ages and gestational age. This work demonstrates a template for determining target attainment for antimicrobials (alone or in combination) in special populations without sufficient available PK data to otherwise assess with traditional pharmacometric methods.

Assessment of flomoxef combined with amikacin in a hollow-fibre infection model for the treatment of neonatal sepsis in low- and middle-income healthcare settings.

BACKGROUND: Annual mortality from neonatal sepsis is an estimated 430 000-680 000 infants globally, most of which occur in low- and middle-income countries (LMICs). The WHO currently recommends a narrow-spectrum ß-lactam (e.g. ampicillin) and gentamicin as first-line empirical therapy. However, available epidemiological data demonstrate high rates of resistance to both agents. Alternative empirical regimens are needed. Flomoxef and amikacin are two off-patent antibiotics with potential for use in this setting. OBJECTIVES: To assess the pharmacodynamics of flomoxef and amikacin in combination. METHODS: The pharmacodynamic interaction of flomoxef and amikacin was assessed in chequerboard assays and a 16-arm dose-ranged hollow-fibre infection model (HFIM) experiment. The combination was further assessed in HFIM experiments mimicking neonatal plasma exposures of clinically relevant doses of both drugs against five Enterobacterales isolates with a range of flomoxef/amikacin MICs. RESULTS: Flomoxef and amikacin in combination were synergistic in bacterial killing in both assays and prevention of emergence of amikacin resistance in the HFIM. In the HFIM assessing neonatal-like drug exposures, the combination killed 3/5 strains to sterility, (including 2/5 that monotherapy with either drug failed to kill) and failed to kill the 2/5 strains with flomoxef MICs of 32 mg/L. CONCLUSIONS: We conclude that the combination of flomoxef and amikacin is synergistic and is a potentially clinically effective regimen for the empirical treatment of neonatal sepsis in LMIC settings and is therefore suitable for further assessment in a clinical trial.

Flomoxef and fosfomycin in combination for the treatment of neonatal sepsis in the setting of highly prevalent antimicrobial resistance.

BACKGROUND: Neonatal sepsis is a serious bacterial infection of neonates, globally killing up to 680 000 babies annually. It is frequently complicated by antimicrobial resistance, particularly in low- and middle-income country (LMIC) settings with widespread resistance to the WHO's recommended empirical regimen of ampicillin and gentamicin. OBJECTIVES: We assessed the utility of flomoxef and fosfomycin as a potential alternative empirical regimen for neonatal sepsis in these settings. METHODS: We studied the combination in a 16-arm dose-ranged hollow-fibre infection model (HFIM) experiment and chequerboard assays. We further assessed the combination using clinically relevant regimens in the HFIM with six Enterobacterales strains with a range of flomoxef/fosfomycin MICs. RESULTS: Pharmacokinetic/pharmacodynamic modelling of the HFIM experimental output, along with data from chequerboard assays, indicated synergy of this regimen in terms of bacterial killing and prevention of emergence of fosfomycin resistance. Flomoxef monotherapy was sufficient to kill 3/3 strains with flomoxef MICs ≤0.5 mg/L to sterility. Three of three strains with flomoxef MICs ≥8 mg/L were not killed by fosfomycin or flomoxef monotherapy; 2/3 of these were killed with the combination of the two agents. CONCLUSIONS: These data suggest that flomoxef/fosfomycin could be an efficacious and synergistic regimen for the empirical treatment of neonatal sepsis in LMIC settings with prevalent antimicrobial resistance. Our HFIM results warrant further assessment of the flomoxef/fosfomycin combination in clinical trials.

Flomoxef for neonates: extending options for treatment of neonatal sepsis caused by ESBL-producing Enterobacterales.

BACKGROUND: Neonatal sepsis is a serious and frequently lethal infection, often complicated by antimicrobial resistance (including ESBLs) in low- and middle-income countries (LMICs). Flomoxef is an off-patent oxacephem ß-lactam with stability against non-AmpC ESBLs, with potential for utility in these settings. To date, there has been no published flomoxef neonatal population pharmacokinetic (PopPK) model. OBJECTIVES: To summarize the clinical data available for flomoxef, build a neonatal PopPK model and assess the adequacy of different neonatal flomoxef regimens. METHODS: A systematic literature search returned all available clinical or pharmacokinetic data of flomoxef use in neonates. Pharmacokinetic data were used to construct a PopPK model, with progressive incorporation of covariates into the final model. Monte Carlo simulations were performed using this final model to simulate drug exposures of different flomoxef regimens to calculate PTAs. RESULTS: Individual-level clinical and pharmacokinetic data were extracted for 313 and 146 neonates, respectively, with population clinical data extracted for a further 199 neonates. Clinical and microbiological success rates were 89.71% and 82.8%, respectively, with minimal side effects. The final PopPK model incorporated body weight and postnatal age as covariates. PTA analyses predicted that IV regimens of 20 mg/kg q12h, 20 mg/kg q6-8h and 40 mg/kg q6-8h are adequate for neonates aged 0-7, 7-14 and 14-28 days, respectively. CONCLUSIONS: To the best of our knowledge, this is the first published neonatal PopPK model for flomoxef. Given the high treatment success rates, low toxicity rates and off-patent status, this drug has potential for use in the treatment of neonatal sepsis in ESBL-prevalent LMIC settings.

Potential Antibiotics for the Treatment of Neonatal Sepsis Caused by Multidrug-Resistant Bacteria.

Neonatal sepsis causes up to an estimated 680,000 deaths annually worldwide, predominantly in low- and middle-income countries (LMICs). A significant and growing proportion of bacteria causing neonatal sepsis are resistant to multiple antibiotics, including the World Health Organization-recommended empiric neonatal sepsis regimen of ampicillin/gentamicin. The Global Antibiotic Research and Development Partnership is aiming to develop alternative empiric antibiotic regimens that fulfil several criteria: (1) affordable in LMIC settings; (2) activity against neonatal bacterial pathogens, including extended-spectrum ß-lactamase producers, gentamicin-resistant Gram-negative bacteria, and methicillin-resistant Staphylococcus aureus (MRSA); (3) a licence for neonatal use or extensive experience of use in neonates; and (4) minimal toxicities. In this review, we identify five antibiotics that fulfil these criteria: amikacin, tobramycin, fosfomycin, flomoxef, and cefepime. We describe the available characteristics of each in terms of mechanism of action, resistance mechanisms, clinical pharmacokinetics, pharmacodynamics, and toxicity profile. We also identify some knowledge gaps: (1) the neonatal pharmacokinetics of cefepime is reliant on relatively small and limited datasets, and the pharmacokinetics of flomoxef are also reliant on data from a limited demographic range and (2) for all reviewed agents, the pharmacodynamic index and target has not been definitively established for both bactericidal effect and emergence of resistance, with many assumed to have an identical index/target to similar class molecules. These five agents have the potential to be used in novel combination empiric regimens for neonatal sepsis. However, the data gaps need addressing by pharmacokinetic trials and pharmacodynamic characterisation.

Amikacin Combined with Fosfomycin for Treatment of Neonatal Sepsis in the Setting of Highly Prevalent Antimicrobial Resistance.

Antimicrobial resistance (particularly through extended-spectrum ß-lactamase and aminoglycoside-modifying enzyme production) in neonatal sepsis is a global problem, particularly in low- and middle-income countries, with significant mortality rates. High rates of resistance are reported for the current WHO-recommended first-line antibiotic regimen for neonatal sepsis, i.e., ampicillin and gentamicin. We assessed the utility of fosfomycin and amikacin as a potential alternative regimen to be used in settings of increasingly prevalent antimicrobial resistance. The combination was studied in a 16-arm dose-ranged hollow-fiber infection model (HFIM) experiment. The combination of amikacin and fosfomycin enhanced bactericidal activity and prevented the emergence of resistance, compared to monotherapy with either antibiotic. Modeling of the experimental quantitative outputs and data from checkerboard assays indicated synergy. We further assessed the combination regimen at clinically relevant doses in the HFIM with nine Enterobacterales strains with high fosfomycin and amikacin MICs and demonstrated successful kill to sterilization for 6/9 strains. From these data, we propose a novel combination breakpoint threshold for microbiological success for this antimicrobial combination against Enterobacterales strains, i.e., MICF × MICA < 256 (where MICF and MICA are the fosfomycin and amikacin MICs, respectively). Monte Carlo simulations predict that a standard fosfomycin-amikacin neonatal regimen would achieve >99% probability of pharmacodynamic success for strains with MICs below this threshold. We conclude that the combination of fosfomycin with amikacin is a viable regimen for the empirical treatment of neonatal sepsis and is suitable for further clinical assessment in a randomized controlled trial.

Microbial aetiology of brain abscess in a UK cohort: Prominent role of Streptococcus intermedius.

BACKGROUND: Brain abscess is an uncommon condition, but carries high mortality. Current treatment guidelines are based on limited data. Surveillance of clinical, radiological and microbiology data is important to inform patient stratification, interventions, and antimicrobial stewardship. METHODS: We undertook a retrospective, observational study of patients with brain abscess, based on hospital coding, in a UK tertiary referral teaching hospital. We reviewed imaging data, laboratory microbiology, and antibiotic prescriptions. RESULTS: Over a 47 month period, we identified 47 adults with bacterial brain abscess (77% male, median age 47 years). Most of the abscesses were solitary frontal or parietal lesions. A microbiological diagnosis was secured in 39/47 (83%) of cases, among which the majority were of the Streptococcus milleri group (27/39; 69%), with a predominance of Streptococcus intermedius (19/27; 70%). Patients received a median of 6 weeks of intravenous antibiotics (most commonly ceftriaxone), with variable oral follow-on regimens. Ten patients (21%) died, up to 146 days after diagnosis. Mortality was significantly associated with increasing age, multiple abscesses, immunosuppression and the presence of an underlying cardiac anomaly. CONCLUSION: Our data suggest that there has been a shift away from staphylococcal brain abscesses, towards S. intermedius as a dominant pathogen. In our setting, empiric current first line therapy with ceftriaxone remains appropriate on microbiological grounds and narrower spectrum therapy may sometimes be justified. Mortality of this condition remains high among patients with comorbidity. Prospective studies are required to inform optimum dose, route and duration of antimicrobial therapy.

A spinal infection with Staphylococcus pseudintermedius.

We present a case of a 60-year-old woman with an invasive spinal infection with Staphylococcus pseudintermedius associated with a 15-year-old spinal fixation device and epidemiological contact with dogs. It was confirmed on blood culture and culture from pus from the epidural abscess and successfully treated using similar treatment as for a Staphylococcus aureus infection - 6 weeks of intravenous flucloxacillin 2 g four times daily with a 6 week follow-on course of oral clindamycin 450 mg three times daily. This case represents the first reported deep abscess forming infection with this recently discovered organism. This case highlights that (1) S. pseudintermedius has a potential for invasive zoonotic infection, (2) treatment as for S. aureus appears adequate for resolution of the case, (3) the increased use of the matrix-assisted laser desorption/ionisation time-of-flight identification technique is leading to more specific identification of previously unrecognised organisms.