Evaluation of Intravenous Fosfomycin Disodium Dosing Regimens in Critically Ill Patients for Treatment of Carbapenem-Resistant Enterobacterales Infections Using Monte Carlo Simulation

Optimized fosfomycin regimens for treating carbapenem-resistant Acinetobacter baumannii in critically ill patients with varying degrees of renal function

Fosfomycin has been used to treat carbapenem-resistant Acinetobacter baumannii (CRAB) infections. However, there is insufficient information on dosage adjustment among critically ill patients with renal impairment. This study aims to evaluate the attainment of PK/PD targets for different dosage regimens of CRAB treatment in critically ill patients based on their renal function. Monte Carlo simulations were conducted to assess the probability of achieving time above the minimum inhibitory concentration (T > MIC) of 80% and 100% and to determine the cumulative fraction response (CFR) against institutional MICs. Our results demonstrated that administering fosfomycin 20-24 g/day to individuals with normal renal function (CrCl ≥60 mL/min) achieved the target at a MIC of ≤64 and ≤32 μg/mL during the first 24 h of treatment and at steady state, respectively. Notably, those with renal impairment achieved higher MIC values at a steady state despite dosage reduction. None of the regimens reached the target CFR. Our study suggested that administering fosfomycin at least 20 g/day to those with normal renal function provides sufficient exposure throughout the treatment course when the MIC value is ≤32 μg/mL. Less aggressive dosing regimens are advisable for patients with renal impairment. Additional clinical studies are necessary to verify our suggestions.

Understanding antimicrobial pharmacokinetics in critically ill patients to optimize antimicrobial therapy: A narrative review

Effective treatment of sepsis not only demands prompt administration of appropriate antimicrobials but also requires precise dosing to enhance the likelihood of patient survival. Adequate dosing refers to the administration of doses that yield therapeutic drug concentrations at the infection site. This ensures a favorable clinical and microbiological response while avoiding antibiotic-related toxicity. Therapeutic drug monitoring (TDM) is the recommended approach for attaining these goals. However, TDM is not universally available in all intensive care units (ICUs) and for all antimicrobial agents. In the absence of TDM, healthcare practitioners need to rely on several factors to make informed dosing decisions. These include the patient's clinical condition, causative pathogen, impact of organ dysfunction (requiring extracorporeal therapies), and physicochemical properties of the antimicrobials. In this context, the pharmacokinetics of antimicrobials vary considerably between different critically ill patients and within the same patient over the course of ICU stay. This variability underscores the need for individualized dosing. This review aimed to describe the main pathophysiological changes observed in critically ill patients and their impact on antimicrobial drug dosing decisions. It also aimed to provide essential practical recommendations that may aid clinicians in optimizing antimicrobial therapy among critically ill patients.

Mortality factors and antibiotic options in carbapenem-resistant Enterobacterales bloodstream infections: Insights from a high-prevalence setting with co-occurring NDM-1 and OXA-48

Bloodstream infections (BSI) caused by carbapenem-resistant Enterobacterales (CRE) are associated with a high mortality rate. This study aimed to investigate factors associated with 14-day mortality and identify a potential treatment option. A retrospective cohort study was conducted on patients with CRE-BSI in Thailand from 2015 to 2020. The multivariate Cox proportional-hazards model was employed to identify factors influencing 14-day mortality. Out of 134 diagnosed cases of CRE-BSI, the all-cause 14-day mortality rate was 35.1%. The most prevalent organism isolated was Klebsiella pneumoniae (85.8%), followed by Escherichia coli (11.9%). Among the 60 isolates tested for carbapenemase genes, the majority exhibited co-occurring blaNDM-1 and blaOXA-48 (51.7%), followed by blaOXA-48 (31.7%) and blaNDM-1 (15.0%). In the multivariate analysis, neutropenia (adjusted hazard ratio [aHR] 2.55; 95% confidence interval [95%CI] 1.28-5.06; p = 0.008), sepsis/septic shock (aHR 3.02; 95%CI 1.33-6.86; p = 0.008), and previous metronidazole exposures (aHR 3.58; 95%CI 1.89-6.71; p < 0.001) were identified as independent factors for 14-day mortality. The fosfomycin-based regimen was found to be protective (aHR 0.37; 95%CI 0.15-0.92; p = 0.032). In patients with CRE-BSI, particularly in regions with a high occurrence of co-occurring blaNDM-1 and blaOXA-48, neutropenia, sepsis/septic shock, and previous metronidazole exposures emerged as independent risk factors for mortality. Moreover, the fosfomycin-based regimen showed an improvement in the survival rate.

Indian consensus on the managemeNt of carbapenem-resistant enterobacterales infection in critically ill patients II (ICONIC II)

INTRODUCTION

The rising challenge of carbapenem-resistant Enterobacterales (CRE) infections in Indian healthcare settings calls for clear clinical guidance on the management of these infections. The Indian consensus on the management of CRE infection in critically ill patients (ICONIC-II) is a follow-up of the ICONIC-I study, which was undertaken in 2019.

AREAS COVERED

A modified Delphi method was used to build expert consensus on CRE management in India, involving online surveys, face-to - face expert meetings, and a literature review. A panel of 12 experts was formed to develop potential clinical consensus statements (CCSs), which were rated through two survey rounds. The CCSs were finalized in a final face-to - face discussion. The finalized CCSs were categorized as consensus, near consensus, and no consensus.

EXPERT OPINION

The outcomes included 46 CCSs (consensus: 40; near consensus: 3; and no consensus: 3). The expert panel discussed and achieved consensus on various strategies for managing CRE infections, emphasizing the significance of existing and emerging resistance mechanisms, prompt and tailored empiric therapy, and use of combination therapies. The consensus statements based on the collective expertise of the panel can potentially assist clinicians in the management of CRE infections that lack high-level evidence.

Comparative effectiveness and mortality of colistin monotherapy versus colistin-fosfomycin combination therapy for the treatment of carbapenem-resistant Enterobacteriaceae (CRE) infections: A propensity score analysis

BACKGROUND

Carbapenem-resistant Enterobacteriaceae (CRE) infections pose a significant threat to global health due to limited treatment options and high mortality rates. Colistin-based regimens have emerged as a primary treatment approach, but the effectiveness and mortality outcomes of colistin monotherapy versus colistin-fosfomycin combination therapy remain uncertain. This study aims to compare the effectiveness and mortality of colistin monotherapy and colistin-fosfomycin combination therapy for CRE infections. Notably, our study is the first to undertake a comprehensive examination of the effectiveness and mortality outcomes between colistin monotherapy and colistin-fosfomycin combination therapy in the context of CRE infections.

METHODS

A retrospective cohort study was conducted using data from patients diagnosed with carbapenem-resistant Enterobacteriaceae (CRE) infections at Nakornping Hospital during 2015 to 2022. Inverse probability weighting (IPW) was employed to create balanced cohorts of patients receiving either colistin monotherapy or colistin-fosfomycin combination therapy. The primary outcome measure was treatment effectiveness, assessed by 30-day mortality. Secondary outcome measures included clinical response, mortality at the end of treatment, and microbiologic response. Univariate and multivariate logistic regression analysis were employed after applying propensity score weighting using inverse probability of weighting (IPW).

RESULTS

A total of 220 patients were included in the analysis, with 67 receiving colistin monotherapy and 153 receiving colistin-fosfomycin combination therapy. Propensity score weighting using IPW balanced the baseline characteristics between the two groups. The effectiveness of treatment, as measured by 30-day mortality, was not significantly different between the colistin monotherapy group and the colistin-fosfomycin combination therapy group (adjusted odds ratio [aOR] = 1.51, 95% confidence interval [CI]: 0.60-3.78, p = 0.383). Similarly, no significant difference was observed in the mortality at the end of treatment between the two groups (aOR = 1.26, 95% CI: 0.55-2.90, p = 0.576). The clinical response (aOR = 1.48, 95% CI: 0.61-3.59, p = 0.383) and microbiologic response (aOR = 0.66, 95% CI: 0.18-2.38, p = 0.527) were similar between the colistin monotherapy and colistin-fosfomycin combination therapy groups.

CONCLUSION

The propensity score analysis among 220 matched patients showed comparable treatment effectiveness and mortality between colistin monotherapy and colistin-fosfomycin combination therapy for CRE infections. These results suggest that colistin monotherapy may be as effective as combination therapy. More prospective randomized controlled trials are needed to confirm these findings and establish optimal CRE treatment strategies.

Pharmacokinetic/pharmacodynamic (PK/PD) simulation for dosage optimization of colistin and sitafloxacin, alone and in combination, against carbapenem-, multidrug-, and colistin-resistant Acinetobacter baumannii

To the best of our knowledge, to date, no study has investigated the optimal dosage regimens of either colistin or sitafloxacin against drug-resistant Acinetobacter baumannii (A. baumannii) infections by using specific parameters. In the current study, we aimed to explore the optimal dosage regimens of colistin and sitafloxacin, either in monotherapy or in combination therapy, for the treatment of carbapenem-, multidrug-, and colistin-resistant A. baumannii infections. A Monte Carlo simulation was applied to determine the dosage regimen that could achieve the optimal probability of target attainment (PTA) and cumulative fraction of response (CFR) (≥90%) based on the specific parameters of each agent and the minimal inhibitory concentration (MIC) of the clinical isolates. This study explored the dosage regimen of 90, 50, 30, and 10 mL/min for patients with creatinine clearance (CrCL). We also explored the dosage regimen for each patient with CrCL using combination therapy because there is a higher possibility of reaching the desired PTA or CFR. Focusing on the MIC90 of each agent in combination therapy, the dosage regimen for colistin was a loading dose of 300 mg followed by a maintenance dose ranging from 50 mg every 48 h to 225 mg every 12 h and the dosage regimen for sitafloxacin was 325 mg every 48 h to 750 mg every 12 h. We concluded that a lower-than-usual dose of colistin based on specific pharmacokinetic data in combination with a higher-than-usual dose of sitafloxacin could be an option for the treatment of carbapenem-, multidrug-, and colistin-resistant. A. baumannii. The lower dose of colistin might show a low probability of adverse reaction, while the high dose of sitafloxacin should be considered. In the current study, we attempted to find if there is a strong possibility of drug selection against crucial drug-resistant pathogen infections in a situation where there is a lack of new antibiotics. However, further study is needed to confirm the results of this simulation study.

Clinical Use of Intravenous Fosfomycin in Critical Care Patients in Taiwan

This retrospective study aimed to evaluate the clinical use and side effects of fosfomycin in critically ill patients in Taiwan. Forty-two patients (mean age, 69.9 years; female, 69%) who received fosfomycin were included from a teaching hospital in Taiwan from January 2021 to December 2021. We analyzed the prescription pattern of intravenous fosfomycin and evaluated patient safety profiles, clinical successes, and microbiological cure rates. The main indication was urinary tract infections (35.6%), and the most frequently identified pathogen was Escherichia coli (18.2%). The overall clinical success was 83.4%, with one multidrug-resistant pathogen isolated from eight patients (19.0%). The average dose of fosfomycin given was 11.1 ± 5.2 g/day. The average duration of therapy was 8.7 ± 5.9 days, with a median duration of 8 days, where fosfomycin was mostly (83.3%) given in combination. Fosfomycin was given 12 hourly to a maximum number (47.6%) of cases. The incidence rates of adverse drug reactions (hypernatremia and hypokalemia) were 33.33% (14/42) and 28.57% (12/42), respectively. The overall survival rate was 73.8%. Intravenous fosfomycin may be an effective and safe antibiotic to use in combination with other drugs for empirical broad-spectrum or highly suspected multidrug-resistant infections in critically ill patients.

Investigations on In Vivo Pharmacokinetic/Pharmacodynamic Determinants of Fosfomycin in Murine Thigh and Kidney Infection Models

Background: Amidst the era of widespread resistance, there has been a renewed interest in older antibiotics such as fosfomycin, owing to its activity against certain resistant Gram-negative pathogens, including multidrug-resistant variants expressing extended spectrum β-lactamases or carbapenemases. The goal of the study was to investigate pharmacokinetic/pharmacodynamic (PK/PD) index and PK/PD targets of fosfomycin in murine thigh and kidney infection models, employing clinical isolates of Escherichia coli (E. coli) and Klebsiella pneumoniae (K. pneumoniae). Methods: Seven isolates of E. coli (one wild-type and six clinical isolates) and five isolates of K. pneumoniae (one wild-type and four clinical isolates) were utilized for in vivo PK/PD studies. Single-dose plasma PK studies were conducted in infected mice by subcutaneous route. PD index was determined from exposure-response analysis employing 24-hr dose fractionation studies in neutropenic murine thigh infection model, while pharmacodynamic targets (PDTs) were derived from both thigh and kidney infection models. Results: Dose fractionation studies demonstrated that in vivo efficacy of fosfomycin best correlated with AUC/MIC for E. coli (R² = 0.9227) and K. pneumoniae (R² = 0.8693). The median AUC/MIC linked to 1 log10 kill effects were 346.2 and 745.2 in thigh infection model and 244.1 and 425.4 in kidney infection model for E. coli and K. pneumoniae, respectively. The mice plasma protein binding of fosfomycin was estimated to be 5.4%. Conclusions: The in vivo efficacy of fosfomycin against Enterobacterales was best described by AUC/MIC. The PDTs derived from this study may help define the coverage potential of fosfomycin at the clinical doses approved.

Prescription Pattern of Intravenous Fosfomycin in a Provincial Hospital in Thailand

BACKGROUND

In Thailand, active antibiotics against Gram-negative bacteria are limited. The re-emergence of intravenous (IV) fosfomycin is an alternative. IV fosfomycin has broad-spectrum activity, relative safety, and availability. The limitations of the clinical use of IV fosfomycin include the lack of susceptibility reports and unclear dosing. Therefore, this study was designed to examine the prescription pattern of IV fosfomycin in Chonburi Hospital, a provincial hospital in Thailand.

MATERIALS AND METHODS

A retrospective descriptive study involving in-patients aged ≥18 years who received IV fosfomycin between February 2019 and January 2020. Data were collected from the electronic patient records.

RESULTS

Of 265 patients, 254 (95.8%) and 11 (4.2%) received IV fosfomycin for treatment and prophylaxis, respectively. IV fosfomycin was prescribed for empirical and definitive treatment. All 166 organisms were Gram-negative bacteria (GNB), including Enterobacterales (47.0%), Acinetobacter baumannii (44.0%), and Pseudomonas aeruginosa (9.0%). Moreover, 141 (87.6%) isolates were carbapenem-resistant GNB (CR-GNB). The most commonly used IV fosfomycin regimen contained colistin or aminoglycosides. Furthermore, 35.3% of the combination regimens contained one active antibiotic. The appropriate dosage of IV fosfomycin for treating urinary tract infection was 71.8%. The 14-day all-cause mortality rate in CR-GNB was 45.0%.

CONCLUSION

IV fosfomycin is reserved for secondary use in treating nosocomial infection with resistant GNB. It is used synergistically with other antibiotics. At least one active antibiotic and the optimal fosfomycin dosage should be considered. An antimicrobial stewardship program should be implemented for the optimal use of fosfomycin.

The burden of carbapenem-resistant Enterobacterales infection in a large Thai tertiary care hospital

Background: Carbapenem-resistant Enterobacterales (CRE) are resistant to several other classes of antimicrobials, reducing treatment options and increasing mortality. We studied the clinical characteristics and burden of hospitalized adult patients with CRE infections in a setting where treatment options are limited.

Methods: A retrospective cohort study included adult inpatients between January 2015–December 2019 at Siriraj Hospital in Bangkok, Thailand. Clinical and microbiological data were reviewed.

Results: Of 420 patients with CRE infections, the mean age was 65.00 ± 18.89 years, 192 (45.72%) were male, and 112 (26.90%) were critically ill. Three hundred and eighty (90.48%) had Klebsiella pneumoniae, and 40 (9.52%) had Escherichia coli infections. The mean APACHE II score was 14.27 ± 6.36. Nearly half had previous hospitalizations (48.81%), 41.2% received antimicrobials, and 88.1% had undergone medical procedures before the onset of infection. The median time of onset of CRE infection was 16 days after admission. Common sites of infection were bacteremia (53.90%) and pneumonia (45.47%). Most CRE-infected patients had septic shock (63.10%) and Gram-negative co-infections (62.85%). Colistin (29.95%) and non-colistin (12.91%) monotherapies, and colistin-based (44.78%) and non-colistin-based (12.36%) combination therapies were the best available antimicrobial therapies (BAAT). The median length of hospitalization was 31 days, and the median hospitalization cost was US$10,435. The in-hospital mortality rate was 68.33%. Septic shock [adjusted odds ratio (aOR) 10.73, 5.65–20.42, p <0 .001], coinfection (aOR 2.43, 1.32–4.47, p = 0.004), mechanical ventilation (aOR 2.33, 1.24–4.36, p = 0.009), and a high SOFA score at onset (aOR 1.18, 1.07–1.30, p <0 .001) were associated with mortality.

Conclusion: CRE infection increases mortality, hospital stays, and healthcare costs. A colistin-based regimen was the BAAT in this study. Therefore, newer antimicrobial agents are urgently needed.

Antimicrobial safety considerations in critically ill patients: part II: focused on anti-microbial toxicities

INTRODUCTION

Antibiotic prescription is a challenging issue in critical care settings. Different pharmacokinetic and pharmacodynamic properties, polypharmacy, drug interactions, and high incidence of multidrug-resistant microorganisms in this population can influence the selection, safety, and efficacy of prescribed antibiotics.

AREAS COVERED

In the current article we searched PubMed, Scopus and Google Scholar for neurotoxicities, hematologic toxicity and fluid stewardship in intensive care units.

EXPERT OPINION

Critically ill patients who receive antimicrobial agents should be monitored for neurological, hematologic toxicities especially seizure, thrombocytopenia, and clostridioides infections. Other toxicities including QTc prolongation, electrolyte disturbances, liver enzyme elevation, and infusion-related reactions were being considered. Other changes, including fluid overload, hypoalbuminemia, augmented renal clearance, increased cardiac outputs in septic shock, and acute kidney injury, may influence treatment efficiency and patient outcome.

High-Dosage Fosfomycin Results in Adequate Plasma and Target-Site Exposure in Morbidly Obese and Nonobese Nonhyperfiltration Patients

The objectives of this study were the identification in (morbidly) obese and nonobese patients of (i) the most appropriate body size descriptor for fosfomycin dose adjustments and (ii) adequacy of the currently employed dosing regimens. Plasma and target site (interstitial fluid of subcutaneous adipose tissue) concentrations after fosfomycin administration (8 g) to 30 surgery patients (15 obese/15 nonobese) were obtained from a prospective clinical trial. After characterization of plasma and microdialysis-derived target site pharmacokinetics via population analysis, short-term infusions of fosfomycin 3 to 4 times daily were simulated. The adequacy of therapy was assessed by probability of pharmacokinetic/pharmacodynamic target attainment (PTA) analysis based on the unbound drug-related targets of an %fT_>MIC (the fraction of time that unbound fosfomycin concentrations exceed the MIC during 24 h) of 70 and an fAUC_0-24h/MIC (the area under the concentration-time curve from 0 to 24 h for the unbound fraction of fosfomycin relative to the MIC) of 40.8 to 83.3. Lean body weight, fat mass, and creatinine clearance calculated via adjusted body weight (ABW) (CLCR_{CG_ABW}) of all patients (body mass index [BMI] = 20.1 to 52.0 kg/m²) explained a considerable proportion of between-patient pharmacokinetic variability (up to 31.0% relative reduction). The steady-state unbound target site/plasma concentration ratio was 26.3% lower in (morbidly) obese than nonobese patients. For infections with fosfomycin-susceptible pathogens (MIC ≤ 16 mg/L), intermittent "high-dosage" intravenous (i.v.) fosfomycin (8 g, three times daily) was sufficient to treat patients with a CLCR_{CG_ABW} of <130 mL/min, irrespective of the pharmacokinetic/pharmacodynamic indices considered. For infections by Pseudomonas aeruginosa with a MIC of 32 mg/L, when the index fAUC_0-24h/MIC is applied, fosfomycin might represent a promising treatment option in obese and nonobese patients, especially in combination therapy to complement β-lactams, in which carbapenem-resistant P. aeruginosa is critical. In conclusion, fosfomycin showed excellent target site penetration in obese and nonobese patients. Dosing should be guided by renal function rather than obesity status. (This study has been registered in the EU Clinical Trials Register under EudraCT no. 2012-004383-22.).

Continuous versus intermittent infusion of antibiotics in Gram-negative multidrug-resistant infections

PURPOSE OF REVIEW

The aim of this review was to perform a critical reappraisal of the real-world evidence supporting administration by prolonged infusion of novel beta-lactams for the management of multidrug-resistant Gram-negative infections.

RECENT FINDINGS

Real-world evidence support the use of novel beta-lactams by prolonged infusion over intermittent infusion in terms of achieving aggressive pharmacokinetic/pharmacodynamic (PK/PD) target for either maximizing efficacy and clinical outcome or suppressing the emergence of resistance development. Continuous infusion of ceftolozane-tazobactam showed a marked superiority toward both intermittent and extended infusion (EI) in achieving a PK/PD target of 100%fT> 4 X MIC in infections caused by less-susceptible Pseudomonas aeruginosa isolates. No resistance development was found in critically ill or immunocompromised patients treated with EI ceftolozane-tazobactam compared to intermittent infusion. Prolonged infusion of ceftazidime-avibactam was negatively associated with mortality in patients affected by Klebsiella pneumoniae carbapenemase-producing K. pneumoniae infections. Different challenging scenarios (patients showing augmented renal clearance of affected by deep-seated infections) could benefit from prolonged infusion to optimize the efficacy of novel agents.

SUMMARY

Although available data are still limited, real-world evidence regarding mainly ceftolozane-tazobactam and ceftazidime-avibactam could support the administration of novel beta-lactams by prolonged infusion in some specific scenarios in which achievement of aggressive PK/PD target is quite challenging.

Fosfomycin and nitrofurantoin: classic antibiotics and perspectives

Antibiotics are essential molecules for the treatment and prophylaxis of many infectious diseases. However, drugs that combat microbial infections can become a human health threat due to their high and often indiscriminate consumption, considered one of the factors of antimicrobial resistance (AMR) emergence. The AMR crisis, the decrease in new drug development by the pharmaceutical industry, and reduced economic incentives for research have all reduced the options for treating infections, and new strategies are necessary, including the return of some traditional but "forgotten" antibiotics. However, prescriptions for these older drugs including nitrofurantoin and oral fosfomycin, have been based on the results of pioneer studies, and the limited knowledge generated 50-70 years ago may not be enough. To avoid harming patients and further increasing multidrug resistance, systematic evaluation is required, mainly for the drugs prescribed for community-acquired infections, such as urinary tract infections (UTI). Therefore, this review has the objective of reporting the use of two classic drugs from the nitrofuran and phosphonic acid classes for UTI control nowadays. Furthermore, we also explore new approaches used for these antibiotics, including new combination regimes for spectral amplification, and the prospects for reducing bacterial resistance in the fight against bacteria responsible for UTI.

Fosfomycin in continuous or prolonged infusion for systemic bacterial infections: a systematic review of its dosing regimen proposal from in vitro, in vivo and clinical studies

Fosfomycin (FOS) administered intravenously has been recently rediscovered for the treatment of systemic infections due to multidrug-resistant bacteria. Its pharmacokinetic properties suggest a time-dependent dosing schedule with more clinical benefits from prolonged (PI) or continuous infusion (CI) than from intermittent infusion. We revised literature concerning PI and CI FOS to identify the best dosing regimen based on current evidence. We performed a MEDLINE/PubMed search. Ninety-one studies and their pertinent references were screened. Seventeen studies were included in the present review. The activity of FOS against Gram-negative and Gram-positive bacteria was evaluated in fourteen and five studies, respectively. Six studies evaluated FOS activity in combination with another antibiotic. Daily dosing of 12, 16, 18 or 24 g, administered with different schedules, were investigated. These regimens resulted active against the tested isolates in most cases. Emergence of resistant isolates has been shown to be preventable through the coadministration of another active antibiotic. FOS is a promising option to treat systemic infections caused by multidrug-resistant bacteria. Coadministration with another active molecule is required to prevent the emergence of resistant bacterial strains. The results of our review suggest that a therapeutic regimen including a loading dose of FOS 8 g followed by a daily dose of 16 g or 24 g CI could be the best therapeutic approach for patients with normal renal function. The dosing regimens in patients with renal insufficiency and CI or PI superiority compared with intermittent infusion in clinical settings should be further investigated.