In vitro activity of fosfomycin trometamol and other oral antibiotics against multidrug-resistant uropathogens

Prevalence, antibiotic resistance pattern for bacteriuria from patients with urinary tract infections

Background and Aims

Antibiotic resistance presents a significant global public health challenge, particularly for urinary tract infections (UTIs), and is notably severe in developing countries. Surveillance of the antimicrobial susceptibility patterns of UTI-causing bacteria is crucial for effective treatment selection. This study aimed to analyze these patterns in bacteria isolated from the urine samples of patients at Mughda Medical College Hospital, Dhaka, Bangladesh.

Methods

A retrospective study (January 2019 to December 2020) at Mugdha Medical College and Hospital, Dhaka, examined clinical and laboratory data from patients with positive urine cultures (≥105 CFU/mL). The study classified patients into four age groups: children (1-<18 years), young adults (18-<33 years), middle-aged adults (33-50 years), and old adults (>50 years). The standard Kirby-Bauer method was used to assess antibiotic sensitivity to 28 common antibiotics.

Results

Among 243 positive urine cultures in both community- and hospital-acquired UTIs, Escherichia coli was the most common uropathogen (65.84%), followed by Klebsiella spp. (12.34%), Enterococcus spp. (8.23%), and other types of bacteria.

Conclusion

Old adults are particularly vulnerable to UTIs, with E. coli being the predominant causative agent in the study region. The observed antimicrobial resistance patterns underscore the necessity of judicious antibiotic selection to effectively treat UTIs across different age groups.

Rediscovering the value of fosfomycin trometamol in the era of antimicrobial resistance: A systematic review and expert opinion

The worldwide prevalence of uncomplicated lower urinary tract infections (uUTIs) caused by multidrug-resistant Escherichia coli is increasing. To address this emergency, international guidelines recommend reducing administration of fluoroquinolones, in the context of growing resistance and the long-lasting and potentially disabling side effects of these drugs. The favoured drug to replace fluoroquinolones is fosfomycin trometamol (FT), a well-known derivate of phosphonic acid with broad-spectrum activity against Gram-negative and Gram-positive bacteria, including multidrug-resistant (MDR) strains. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) recently reduced the susceptibility breakpoint for E. coli from 32 mg/L to 8 mg/L regarding FT used for uUTIs. This might lead to increased appropriate use of oral fosfomycin target therapy against E. coli and other microorganisms, and may be associated with a high likelihood of success. For species such as Klebsiella spp, particularly MDR strains, the absence of clinical breakpoints might lead to reduced use of oral fosfomycin, particularly if minimum inhibitory concentration is not available. To address this issue, this review presents an overview of the preclinical evidence on the activity of FT, and a systematic review of the clinical activity of FT in uUTIs in women, and in the prevention of infectious complications after prostate biopsy. The findings indicate that the safety and microbiological and clinical effectiveness of a single oral dose of FT are similar to that for comparator regimens with longer treatment schedules in women with uUTI, and FT can be considered a viable alternative to fluoroquinolones for antimicrobial prophylaxis in prostate biopsy. These observations and a broad clinical experience support the empirical use of FT for treating uUTI and indicate that FT is a promising candidate to effectively counteract antibiotic-resistant uUTIs throughout Europe.

Oral fosfomycin for treatment of acute bacterial prostatitis caused by multidrug-resistant Enterobacterales

To assess the feasibility of oral fosfomycin-tromethamine (FT) for the management of acute bacterial prostatitis (ABP) caused by multidrug-resistant (MDR) Enterobacterales. An observational study of adult patients diagnosed with ABP from Vall d'Hebron University Hospital (Barcelona, Spain), treated with oral FT. The primary outcome was clinical cure defined as symptom relief at the control visit, 2-4 weeks post-end of treatment. Secondary outcomes included microbiological cure, relapse, and adverse events related to the treatment. Eighteen patients with ABP caused by Enterobacterales (15 Escherichia coli and three Klebsiella pneumoniae) were included. Microorganisms were MDR bacteria [14 extended-spectrum beta-lactamase (ESBL) producers and two carbapenemase producing K. pneumoniae]. Patients received treatment with FT 3 g/48 hours during a median of 14 days (Q25-Q75, 12-17.75). Fifteen patients received a lead-in phase of intravenous suitable antimicrobial during a median of 7 days (Q25-Q75, 3.75-8). No patient had to stop treatment due to adverse events, and the only side effect reported in two patients was diarrhea. Clinical cure was achieved in all (18/18) patients and microbiological cure in 11/12 patients. After a median of follow-up of 5 months (Q25-Q75, 2-11), 2/18 patients relapsed with an orchitis and a new episode of ABP. FT is an attractive step-down therapy for ABP in patients with resistance or side effects to first-line drugs. The availability of oral treatment could reduce the use of the carbapenems, with a benefit in the quality of life of the patient, health costs, and an ecological impact. IMPORTANCE We present a brief but largest and interesting experience in which we use fosfomycin-tromethamine (FT) for the treatment of acute bacterial prostatitis (ABP) due to multiresistant bacteria. Our study provides new data that help to consider FT as a plausible alternative for treating ABP in patients with resistance or side effects to first-line drugs. The availability of an alternative oral treatment to avoid the use of the carbapenems could have important benefits in terms of quality of life of the patient, health costs, and an ecological impact.

Uropathogenic Escherichia coli endeavors: an insight into the characteristic features, resistance mechanism, and treatment choice

Uropathogenic Escherichia coli (UPEC) are the strains diverted from the intestinal status and account mainly for uropathogenicity. This pathotype has gained specifications in structure and virulence to turn into a competent uropathogenic organism. Biofilm formation and antibiotic resistance play an important role in the organism's persistence in the urinary tract. Increased consumption of carbapenem prescribed for multidrug-resistant (MDR) and Extended-spectrum-beta lactamase (ESBL)-producing UPECs, has added to the expansion of resistance. The World Health Organization (WHO) and Centre for Disease Control (CDC) placed the Carbapenem-resistant Enterobacteriaceae (CRE) on their treatment priority lists. Understanding both patterns of pathogenicity, and multiple drug resistance may provide guidance for the rational use of anti-bacterial agents in the clinic. Developing an effective vaccine, adherence-inhibiting compounds, cranberry juice, and probiotics are non-antibiotical approaches proposed for the treatment of drug-resistant UTIs. We aimed to review the distinguishing characteristics, current therapeutic options and promising non-antibiotical approaches against ESBL-producing and CRE UPECs.

Virulence analysis and antibiotic resistance of Klebsiella pneumoniae isolates from hospitalised patients in Poland

Klebsiella pneumoniae (KP) is a nosocomial pathogen causing difficult-to-treat infections. The presence of virulence genes and antibiotic resistance of 109 KP isolates from hospitalized patients were investigated. Among them, 68.8% were multi-drug resistant (MDR) and 59.6% produced extended-spectrum beta-lactamases (ESBLs). Metallo-β-lactamases (MBLs) were produced by 22% of isolates (mainly from anus), including 16.5% of isolates producing New Delhi metallo-β-lactamase (NDM-1). The genes encoding adhesins (fimH-91.7%, mrkD-96.3%), enterobactin (entB-100%) and yersiniabactin (irp-1-88%) were frequently identified. The genes encoding salmochelin (iroD-9.2%, iroN-7.3%) and colibactin (clbA, clbB-0.9%) were identified rarely. Iron acquisition system-related kfu gene and wcaG gene involved in capsule production were identified in 6.4% and 11% of isolates, respectively. The rmpA gene associated with hypermucoviscosity was present in 6.4% of isolates. In 19.2% of isolates magA gene was detected, specific for K1 capsule serotype, while 22.9% of isolates showed K2 capsule serotype. The rmpA, iroD or iroN genes being diagnostic biomarkers for hypervirulent KP (hvKP) were detected in 16.5% of isolates. We found that 55.5% of hvKP were MDR and produced ESBLs, thus hospital KP isolates pose a serious threat to the healthcare system.

Fosfomycin Disk Diffusion Testing among Klebsiella pneumoniae Results in Frequent Inner Colonies and Categorical Disagreement Based on Conflicting Breakpoint Organization Recommendations

Recent studies indicate that discrete inner colonies (ICs) arise during fosfomycin disk diffusion (DD) testing. CLSI and EUCAST have contradicting recommendations on the interpretation of ICs; CLSI recommends considering them while EUCAST recommends ignoring them when interpreting DD results. We sought to compare the categorical agreement of DD and agar dilution (AD) MIC and to assess the implications of ICs interpretation on zone diameter readings. A convenience sample of 80 Klebsiella pneumoniae clinical isolates with varied phenotypic profiles collected from 3 United States locations was included. Susceptibility was determined in duplicate, using both organization recommendations and interpretations for Enterobacterales. Correlations between methods were calculated using EUCASTIV AD as the reference method. MIC values ranged from 1 to >256 μg/mL with an MIC50/90 of 32/256 μg/mL. Extrapolating EUCASToral and CLSI AD Escherichia coli breakpoints, 12.5% and 83.8% of isolates were susceptible, respectively, whereas 66.3% were susceptible by EUCASTIV AD-which applies to K. pneumoniae. CLSI DD measurements were 2 to 13 mm smaller than EUCAST measurements due to 66 (82.5%) isolates producing discrete ICs. Categorical agreement with EUCASTIV AD was greatest for CLSI AD (65.0%) and poorest for EUCASToral DD (6.3%). Isolates among this collection were frequently classified into different interpretive categories based on varying breakpoint organization recommendations. The more conservative oral breakpoints of EUCAST resulted in more isolates categorized as resistant despite frequent ICs. Differing zone diameter distributions and poor categorical agreement highlight issues of extrapolating E. coli breakpoints and methods to other Enterobacterales, and the clinical relevance of this issue warrants further investigation. IMPORTANCE Fosfomycin susceptibility testing recommendations are complex. Both the Clinical and Laboratory Standards Institute and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) recognize agar dilution as the reference method, but they also support disk diffusion as an approved method for Escherichia coli. However, these two organizations have conflicting recommendations for the interpretation of inner colonies that arise during disk diffusion testing which can lead to varying zone diameters and interpretations despite isolates having identical MIC values. Using a collection of 80 Klebsiella pneumoniae isolates, we found that a large (82.5%) portion produced discrete inner colonies during disk diffusion and isolates were frequently classified into different interpretive categories. The more conservative breakpoints of EUCAST resulted in more isolates categorized as resistant despite frequent inner colonies. Differing zone diameter distributions and poor categorical agreement highlight issues of extrapolating E. coli breakpoints and methods to other Enterobacterales, and the clinical relevance of this issue warrants further investigation.

Carbapenem-Resistant Klebsiella pneumoniae: Virulence Factors, Molecular Epidemiology and Latest Updates in Treatment Options

Klebsiella pneumoniae is a Gram-negative opportunistic pathogen responsible for a variety of community and hospital infections. Infections caused by carbapenem-resistant K. pneumoniae (CRKP) constitute a major threat for public health and are strongly associated with high rates of mortality, especially in immunocompromised and critically ill patients. Adhesive fimbriae, capsule, lipopolysaccharide (LPS), and siderophores or iron carriers constitute the main virulence factors which contribute to the pathogenicity of K. pneumoniae. Colistin and tigecycline constitute some of the last resorts for the treatment of CRKP infections. Carbapenemase production, especially K. pneumoniae carbapenemase (KPC) and metallo-β-lactamase (MBL), constitutes the basic molecular mechanism of CRKP emergence. Knowledge of the mechanism of CRKP appearance is crucial, as it can determine the selection of the most suitable antimicrobial agent among those most recently launched. Plazomicin, eravacycline, cefiderocol, temocillin, ceftolozane-tazobactam, imipenem-cilastatin/relebactam, meropenem-vaborbactam, ceftazidime-avibactam and aztreonam-avibactam constitute potent alternatives for treating CRKP infections. The aim of the current review is to highlight the virulence factors and molecular pathogenesis of CRKP and provide recent updates on the molecular epidemiology and antimicrobial treatment options.

Assessing Clinical Potential of Old Antibiotics against Severe Infections by Multi-Drug-Resistant Gram-Negative Bacteria Using In Silico Modelling

In the light of increasing antimicrobial resistance among gram-negative bacteria and the lack of new more potent antimicrobial agents, new strategies have been explored. Old antibiotics, such as colistin, temocillin, fosfomycin, mecillinam, nitrofurantoin, minocycline, and chloramphenicol, have attracted the attention since they often exhibit in vitro activity against multi-drug-resistant (MDR) gram-negative bacteria, such as Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii. The current review provides a summary of the in vitro activity, pharmacokinetics and PK/PD characteristics of old antibiotics. In silico modelling was then performed using Monte Carlo simulation in order to combine all preclinical data with human pharmacokinetics and determine the probability of target (1-log kill in thigh/lung infection animal models) attainment (PTA) of different dosing regimens. The potential of clinical efficacy of a drug against severe infections by MDR gram-negative bacteria was considered when PTA was >95% at the epidemiological cutoff values of corresponding species. In vitro potent activity against MDR gram-negative pathogens has been shown for colistin, polymyxin B, temocillin (against E. coli and K. pneumoniae), fosfomycin (against E. coli), mecillinam (against E. coli), minocycline (against E. coli, K. pneumoniae, A. baumannii), and chloramphenicol (against E. coli) with ECOFF or MIC90 ≤ 16 mg/L. When preclinical PK/PD targets were combined with human pharmacokinetics, Monte Carlo analysis showed that among the old antibiotics analyzed, there is clinical potential for polymyxin B against E. coli, K. pneumoniae, and A. baumannii; for temocillin against K. pneumoniae and E. coli; for fosfomycin against E. coli and K. pneumoniae; and for mecillinam against E. coli. Clinical studies are needed to verify the potential of those antibiotics to effectively treat infections by multi-drug resistant gram-negative bacteria.

Efficacy of Fosfomycin against Planktonic and Biofilm-Associated MDR Uropathogenic Escherichia coli Clinical Isolates

Urinary tract infections (UTI) are a severe public health problem and are caused mainly by the uropathogenic Escherichia coli (UPEC). Antimicrobial resistance and limited development of new antimicrobials have led to the reuse of old antibiotics such as fosfomycin. The aim of this study was to evaluate the in vitro efficacy of fosfomycin on a collection of multidrug-resistant (MDR) UPEC and the degradative activity on biofilm producers. A total of 100 MDR UPEC clinical isolates were collected from patients at Mexican second- and third-level hospitals. Microorganism identification was performed using an automated system, the evaluation of the susceptibility of clinical isolates to fosfomycin was performed using the resazurin microtiter assay, and the identification of biofilm producers and the effect of fosfomycin in biofilms were evaluated using the crystal violet method. Among planktonic MDR UPEC, 93% were susceptible to fosfomycin. Eighty-three MDR UPEC were categorized as weak (39.8%), moderate (45.2%), and strong (14.5%) biofilm producers. Fosfomycin exhibited degradative activity ranging from 164.4 µg/mL to 1045 µg/mL. Weak producers required statistically lower concentrations of fosfomycin to destroy the biofilm, contrary to moderate and strong producers. In conclusion, fosfomycin could be an option for the treatment of infections caused by MDR UPEC, for which the antimicrobial treatment is more often becoming limited.

In Vitro Susceptibility of Multi-Drug Resistant Klebsiellapneumoniae Strains Causing Nosocomial Infections to Fosfomycin. A Comparison of Determination Methods

INTRODUCTION

Over the past few decades, Klebsiella pneumoniae strains increased their pathogenicity and antibiotic resistance, thereby becoming a major therapeutic challenge. One of the few available therapeutic options seems to be intravenous fosfomycin. Unfortunately, the determination of sensitivity to fosfomycin performed in hospital laboratories can pose a significant problem. Therefore, the aim of the present research was to evaluate the activity of fosfomycin against clinical, multidrug-resistant Klebsiella pneumoniae strains isolated from nosocomial infections between 2011 and 2020, as well as to evaluate the methods routinely used in hospital laboratories to assess bacterial susceptibility to this antibiotic.

MATERIALS AND METHODS

43 multidrug-resistant Klebsiella strains isolates from various infections were tested. All the strains had ESBL enzymes, and 20 also showed the presence of carbapenemases. Susceptibility was determined using the diffusion method (E-test) and the automated system (Phoenix), which were compared with the reference method (agar dilution).

RESULTS

For the reference method and for the E-test, the percentage of strains sensitive to fosfomycin was 65%. For the Phoenix system, the percentage of susceptible strains was slightly higher and stood at 72%. The percentage of fosfomycin-resistant strains in the Klebsiella carbapenemase-producing group was higher (45% for the reference method and E-test and 40% for the Phoenix method) than in carbapenemase-negative strains (25%, 25%, and 20%, respectively). Full (100%) susceptibility categorical agreement was achieved for the E-test and the reference method. Agreement between the automated Phoenix system and the reference method reached 86%.

CONCLUSIONS

Fosfomycin appears to be the antibiotic with a potential for use in the treatment of infections with multidrug-resistant Klebsiella strains. Susceptibility to this drug is exhibited by some strains, which are resistant to colistin and carbapenems. The E-test, unlike the Phoenix method, can be an alternative to the reference method in the routine determination of fosfomycin susceptibility, as it shows agreement in terms of sensitivity categories and only slight differences in MIC values. The Phoenix system, in comparison to the reference method, shows large discrepancies in the MIC values and in the susceptibility category.

Efficacy and safety of oral fosfomycin for asymptomatic bacteriuria in kidney transplant recipients: Results from a Spanish multicenter cohort

Current guidelines recommend against systematic screening or treating asymptomatic bacteriuria (AB) among kidney transplant (KT) recipients, although the evidence regarding episodes occurring early after transplantation or in the presence of anatomical abnormalities is inconclusive. Oral fosfomycin may constitute a good option for the treatment of post-transplant AB, particularly due to the emergence of multidrug-resistant (MDR) uropathogens. Available clinical evidence supporting its use in this specific setting, however, remains scarce. We performed a retrospective study in 14 Spanish institutions from January 2005 to December 2017. Overall, 137 episodes of AB diagnosed in 133 KT recipients treated with oral fosfomycin (calcium and trometamol salts) with a test-of-cure urine culture within the first 30 days were included. Median time from transplantation to diagnosis was 3.1 months (interquartile range [IQR]: 1.1 - 10.5). Most episodes (96.4% [132/137]) were caused by gram-negative bacteria (GNB), and 56.9% (78/137) were categorized as MDR (extended-spectrum β-lactamase-producing Enterobacterales [20.4%] and carbapenem-resistant GNB [2.9%]). Rate of microbiological failure at month 1 was 40.1% (95% confidence interval [95%CI]: 31.9 - 48.9) for the whole cohort and 42.3% (95%CI: 31.2 - 54.0) for episodes due to MDR pathogens. Previous urinary tract infection (odds ratio [OR]: 2.42; 95%CI: 1.11 - 5.29; P-value = 0.027) and use of fosfomycin as salvage therapy (OR: 8.31; 95%CI: 1.67 - 41.35; P-value = 0.010) were predictors of microbiological failure. No severe treatment-related adverse event were detected. Oral fosfomycin appears to be a suitable and safe alternative for the treatment (if indicated) of AB after KT, including those episodes due to MDR uropathogens.

Virulence Factors in Coagulase-Negative Staphylococci

Coagulase-negative staphylococci (CoNS) have emerged as major pathogens in healthcare-associated facilities, being S. epidermidis, S. haemolyticus and, more recently, S. lugdunensis, the most clinically relevant species. Despite being less virulent than the well-studied pathogen S. aureus, the number of CoNS strains sequenced is constantly increasing and, with that, the number of virulence factors identified in those strains. In this regard, biofilm formation is considered the most important. Besides virulence factors, the presence of several antibiotic-resistance genes identified in CoNS is worrisome and makes treatment very challenging. In this review, we analyzed the different aspects involved in CoNS virulence and their impact on health and food.

In vitro activity of fosfomycin against mucoid and non-mucoid Pseudomonas aeruginosa strains

OBJECTIVES

Pseudomonas aeruginosa is the most frequent infectious agent in cystic fibrosis patients. P. aeruginosa resistance to first line antibiotics limits therapeutic options, but the therapeutic potential of older generation antibiotics, such as fosfomycin is under investigation. Fosfomycin does not belong to any other antibiotic class and acts by inhibiting the biosynthesis of the bacterial cell wall during the initial phases. A major problem for the use of fosfomycin against P. aeruginosa is the absence of a clinical breakpoint, the last one of 32 μg/mL was proposed in 2013 by the CA-SFM (Comité de l'Antibiogramme de la Société Française de Microbiologie).

METHODS

Sixty-one strains of P. aeruginosa (thirty mucoid and thirty-one non mucoid) were collected from respiratory samples of cystic fibrosis patients. All isolates were identified by MALDI-TOF (Bruker, Bremen, Germany). Fosfomycin MICs against P. aeruginosa were measured using an automated system and confirmed by the gold standard method.

RESULTS

There was no significant difference between mucoid and non-mucoid strains. MIC distribution and susceptibility rates were obtained by agar dilution method and from this data we measured MIC50 and MIC90 which were equal to 32 μg/mL and 64 μg/mL, respectively. From automated method results we measured a very major error (VME), major error (ME) and categorical agreement (CA) which were equal to 0%, 11% and 89%, respectively. Comparing automated and agar dilution methods, a Cohen's kappa equal to 73% (0.726) was measured.

CONCLUSIONS

Our data suggest that fosfomycin has good effect against mucoid and non-mucoid strains of P. aeruginosa and automated systems can be implemented in clinical microbiology laboratories to assess fosfomycin with rapid and reproducible results.

Treatment of urinary tract infections in the era of antimicrobial resistance and new antimicrobial agents

Urinary tract infections (UTIs) caused by antibiotic-resistant Gram-negative bacteria are a growing concern due to limited treatment options. Knowledge of the common uropathogens in addition to local susceptibility patterns is essential in determining appropriate empiric antibiotic therapy of UTIs. The recommended first-line empiric antibiotic therapy for acute uncomplicated bacterial cystitis in otherwise healthy adult nonpregnant females is a 5-day course of nitrofurantoin, a 3-g single dose of fosfomycin tromethamine, or a 5-day course of pivmecillinam. High rates of resistance for trimethoprim-sulfamethoxazole and ciprofloxacin preclude their use as empiric treatment of UTIs in several communities, particularly if patients who were recently exposed to them or in patients who are at risk of infections with extended-spectrum β-lactamases (ESBLs)-producing Enterobacteriales. Second-line options include oral cephalosporins such as cephalexin or cefixime, fluoroquinolones and β-lactams, such as amoxicillin-clavulanate. Current treatment options for UTIs due to AmpC- β -lactamase-producing Enterobacteriales include nitrofurantoin, fosfomycin, pivmecillinam, fluoroquinolones, cefepime, piperacillin-tazobactam and carbapenems. Treatment oral options for UTIs due to ESBLs-E coli include nitrofurantoin, fosfomycin, pivmecillinam, amoxicillin-clavulanate, finafloxacin, and sitafloxacin while pivmecillinam, fosfomycin, finafloxacin, and sitafloxacin are treatment oral options for ESBLs- Klebsiella pneumoniae. Parenteral treatment options for UTIs due to ESBLs-producing Enterobacteriales include piperacillin-tazobactam (for ESBL-E coli only), carbapenems including meropenem/vaborbactam, imipenem/cilastatin-relebactam, and sulopenem, ceftazidime-avibactam, ceftolozane-tazobactam, aminoglycosides including plazomicin, cefiderocol, fosfomycin, sitafloxacin, and finafloxacin. Ceftazidime-avibactam, meropenem/vaborbactam, imipenem/cilastatin-relebactam, colistin, fosfomycin, aztreonam and ceftazidime-avibactam, aztreonam and amoxicillin-clavulanate, aminoglycosides including plazomicin, cefiderocol, tigecycline are treatment options for UTIs caused by carbapenem-resistant Enterobacteriales (CRE). Treatment options for UTIs caused by multidrug resistant (MDR)-Pseudomonas spp. include fluoroquinolones, ceftazidime, cefepime, piperacillin-tazobactam, carbapenems including imipenem-cilastatin/relebactam, meropenem, and fosfomycin, ceftolozane-tazobactam, ceftazidime-avibactam, aminoglycosides including plazomicin, aztreonam and ceftazidime-avibactam, cefiderocol, and colistin. It is important to use the new antimicrobials wisely for treatment of UTIs caused by MDR-organisms to avoid resistance development.

Urinary antibacterial activity of fosfomycin and nitrofurantoin at registered dosages in healthy volunteers

Given emerging uropathogen resistance to more recent antibiotics, old antibiotics used for uncomplicated urinary tract infection (UTI) warrant re-examination. In this study, the urinary antibacterial activities of fosfomycin and nitrofurantoin were investigated by determining the urinary inhibitory titre and urinary bactericidal titre against uropathogens in urine samples from female volunteers following administration of single-dose fosfomycin (3 g) or nitrofurantoin (50 mg q6h or 100 mg q8h). Urine samples were collected over 48 h (fosfomycin) or 6 or 8 h (nitrofurantoin), with drug levels quantified with every void. Fosfomycin concentrations ranged from <0.75 mg/L [lower limit of quantification (LLOQ)] to 5729.9 mg/L and nitrofurantoin concentrations ranged from <4 mg/L (LLOQ) to 176.3 mg/L (50 mg q6h) or 209.4 mg/L (100 mg q8h). There was discrepancy in the response to fosfomycin between Escherichia coli and Klebsiella pneumoniae, with fosfomycin displaying strong bactericidal activity for 48 h against E. coli but moderate bactericidal activity for 18 h against K. pneumoniae. This effect was not related to the strain's baseline minimum inhibitory concentration but rather to the presence of a resistant subpopulation. Maximum titres of nitrofurantoin were obtained during the first 2 h, but no antibacterial effect was found in most samples regardless of the dose. In the rare samples in which antibacterial activity was detectable, titres were comparable for both species tested. These findings confirm doubts regarding fosfomycin administration in UTIs caused by K. pneumoniae and reveal a discrepancy between nitrofurantoin's measurable ex vivo activity and its clinical effect over multiple dosing intervals.

Resistenze antibiotiche e nuove molecole: qual è lo scenario attuale?

Antibiotic resistance and new drugs in urologic setting: what we need to know? Urinary tract infections (UTIs) are among the most frequent infectious diseases, and represent an important public health problem with a substantial economic burden. In recent years the chemoresistance of the main uropathogens has significantly increased worldwide. Extended spectrum beta-lactamase (ESBL) production and multi-drug resistant (MDR) clones of Escherichia coli and Klebsiella pneumoniae are limiting available treatment options. Carbapenems and aminoglycosides are still effective in complicated UTI. New beta-lactam combinations such as ceftolozane-tazobactam and ceftazidime-avibactam may be highly useful in treating severe infections while contributing to the carbapenem sparing strategy. For uncomplicated UTI, within older antibiotics, fosfomycin trometamol may be considered a first-choice drug since it is still retaining a good activity against MDR uropathogens. On the other hand, there are extensive data showing that the administration of antimicrobials according to pharmacokinetic/pharmacodynamic (PK/PD) parameters improves the possibility of a positive clinical outcome, particularly in severely ill patients. Evidence is growing that when PK/PD parameters are used to target not only clinical cure. This article discusses the PK/PD characteristics of antimicrobial agents for the treatment of UTIs, and the pharmacological and therapeutic strategies for limiting or preventing bacterial resistance.

Optimizing dosing of nitrofurantoin from a PK/PD point of view: What do we need to know?

Nitrofurantoin is an old antibiotic and an important first-line oral antibiotic for the treatment of uncomplicated urinary tract infections. However despite its long term use for over 60 years, little information is available with respect to its dose justification and this may be the reason of highly variable recommended doses and dosing schedules. Furthermore, nitrofurantoin is not a uniform product -crystal sizes of nitrofurantoin, and therefore pharmacokinetic properties, differ significantly by product. Moreover, pharmacokinetic profiling of some products is even lacking, or difficult to interpret because of its unstable chemical properties. Pharmacokinetic and pharmacodynamic data is now slowly becoming available. This review provides an overview of nitrofurantoins antibacterial, pharmacokinetic and pharmacodynamic properties. This shows that a clear rationale of current dosing regimens is scanty.

High rate of colistin and fosfomycin resistance among carbapenemase-producing Enterobacteriaceae in Turkey

When the problem with carbapenem-resistant Enterobacteriaceae (CRE) increases, the older antimicrobial agents such as colistin and fosfomycin are used for the treatment of these infections. In this study, the broth microdilution method for colistin and the agar dilution method for fosfomycin were used for a total of 147 multidrug-resistant (MDR) or extensively drug-resistant (XDR) strains of CRE. The study included Klebsiella pneumoniae (91.16%), Escherichia coli (7.48%), Enterobacter cloacae (0.68%), and Serratia marcescens (0.68%). All these strains produce various types of carbapenemase, including OXA-48, NDM, and KPC. Some of these strains also have three different carbapenemase mechanisms, including OXA-48 (78.23%), NDM (2.04%), and KPC (0.68%) or OXA-48 and NDM (10.88%), or OXA-48 and KPC (0.68%). About 76.19% of the strains and 67.35% of the strains were resistant for colistin and fosfomycin, respectively. A total of 21 out of 35 colistin-susceptible strains were found to be susceptible to fosfomycin. This study showed that the resistance rates of colistin and fosfomycin are high. The MDR and XDR strains of CRE are spreading in our region and thus a monitoring system for CRE should be followed. Moreover, the applicability of antimicrobial stewardship programs should be increased in all inpatient and outpatient settings.

Multi-drug-resistant Gram-negative bacteria causing urinary tract infections: a review

Urinary tract infections (UTIs) are among the most frequent infectious diseases affecting humans, and represent an important public health problem with a substantial economic burden. Due to the high empiric use of antibiotics for the treatment of UTI, antibacterial resistance of Enterobacteriaceae, specifically the main uropathogens Escherichia coli and Klebsiella pneumoniae, has significantly increased worldwide. In this article the worldwide epidemiology of resistant Gram-negative bacteria causing UTIs, with a special focus on extended spectrum beta lactamase (ESBL) positive pathogens, as well as new threats such as multi-drug-resistant (MDR) clones (e.g. E. coli 131 (ST131) and K. pneumoniae ST258), are reviewed. The increased prevalence of MDR Enterobacteriaceae, limiting available treatment options for infections caused by these organisms, and the lack of new antibiotics provide good rationale for using older antibiotics, such as fosfomycin, that have been shown to retain some activity against MDR bacteria.

Pharmacological properties of oral antibiotics for the treatment of uncomplicated urinary tract infections

The therapeutic management of uncomplicated bacterial urinary tract infections (UTIs) is based on short-term courses of oral antibiotics. The preferred drugs are nitrofurantoin trimethoprim-sulfamethoxazole, fosfomycin trometamol, fluoroquinolones and β-lactam agents. The choice of agent for treating uncomplicated UTIs should be based on the pharmacokinetic characteristics of the molecule so that clinical benefit is optimized and the risk of antibacterial resistance is minimized. This article discusses the general pharmacokinetic-pharmacodynamic (PK/PD) aspects of antimicrobial chemotherapy, the PK/PD characteristics of oral antimicrobial agents for the treatment of uncomplicated UTIs and the pharmacological and therapeutic strategies for limiting or preventing bacterial resistance.

Effect of 5-Day Nitrofurantoin vs Single-Dose Fosfomycin on Clinical Resolution of Uncomplicated Lower Urinary Tract Infection in Women: A Randomized Clinical Trial

IMPORTANCE

The use of nitrofurantoin and fosfomycin has increased since guidelines began recommending them as first-line therapy for lower urinary tract infection (UTI).

OBJECTIVE

To compare the clinical and microbiologic efficacy of nitrofurantoin and fosfomycin in women with uncomplicated cystitis.

DESIGN, SETTING, AND PARTICIPANTS

Multinational, open-label, analyst-blinded, randomized clinical trial including 513 nonpregnant women aged 18 years and older with symptoms of lower UTI (dysuria, urgency, frequency, or suprapubic tenderness), a positive urine dipstick result (with detection of nitrites or leukocyte esterase), and no known colonization or previous infection with uropathogens resistant to the study antibiotics. Recruitment took place from October 2013 through April 2017 at hospital units and outpatient clinics in Geneva, Switzerland; Lodz, Poland; and Petah-Tiqva, Israel.

INTERVENTIONS

Participants were randomized in a 1:1 ratio to oral nitrofurantoin, 100 mg 3 times a day for 5 days (n = 255), or a single 3-g dose of oral fosfomycin (n = 258). They returned 14 and 28 days after therapy completion for clinical evaluation and urine culture collection.

MAIN OUTCOMES AND MEASURES

The primary outcome was clinical response in the 28 days following therapy completion, defined as clinical resolution (complete resolution of symptoms and signs of UTI without prior failure), failure (need for additional or change in antibiotic treatment due to UTI or discontinuation due to lack of efficacy), or indeterminate (persistence of symptoms without objective evidence of infection). Secondary outcomes included bacteriologic response and incidence of adverse events.

RESULTS

Among 513 patients who were randomized (median age, 44 years [interquartile range, 31-64]), 475 (93%) completed the trial and 377 (73%) had a confirmed positive baseline culture. Clinical resolution through day 28 was achieved in 171 of 244 patients (70%) receiving nitrofurantoin vs 139 of 241 patients (58%) receiving fosfomycin (difference, 12% [95% CI, 4%-21%]; P = .004). Microbiologic resolution occurred in 129 of 175 (74%) vs 103 of 163 (63%), respectively (difference, 11% [95% CI, 1%-20%]; P = .04). Adverse events were few and primarily gastrointestinal; the most common were nausea and diarrhea (7/248 [3%] and 3/248 [1%] in the nitrofurantoin group vs 5/247 [2%] and 5/247 [1%] in the fosfomycin group, respectively).

CONCLUSIONS AND RELEVANCE

Among women with uncomplicated UTI, 5-day nitrofurantoin, compared with single-dose fosfomycin, resulted in a significantly greater likelihood of clinical and microbiologic resolution at 28 days after therapy completion.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT01966653.

Oral Fosfomycin for the Treatment of Acute and Chronic Bacterial Prostatitis Caused by Multidrug-Resistant Escherichia coli

Acute and chronic bacterial prostatitis in outpatients is commonly treated with oral fluoroquinolones; however, the worldwide dissemination of multidrug-resistant (MDR) Escherichia coli has resulted in therapeutic failures with fluoroquinolones. We reviewed the literature regarding the use of oral fosfomycin in the treatment of acute and chronic prostatitis caused by MDR E. coli. All English-language references on PubMed from 1986 to June 2017, inclusive, were reviewed from the search “fosfomycin prostatitis.” Fosfomycin demonstrates potent in vitro activity against a variety of antimicrobial-resistant E. coli genotypes/phenotypes including ciprofloxacin-resistant, trimethoprim-sulfamethoxazole-resistant, extended-spectrum β-lactamase- (ESBL-) producing, and MDR isolates. Fosfomycin attains therapeutic concentrations (≥4 μg/g) in uninflamed prostatic tissue and maintains a high prostate/plasma ratio up to 17 hours after oral administration. Oral fosfomycin's clinical cure rates in the treatment of bacterial prostatitis caused by antimicrobial-resistant E. coli ranged from 50 to 77% with microbiological eradication rates of >50%. An oral regimen of fosfomycin tromethamine of 3 g·q 24 h for one week followed by 3 g·q 48 h for a total treatment duration of 6–12 weeks appeared to be effective. Oral fosfomycin may represent an efficacious and safe treatment for acute and chronic prostatitis caused by MDR E. coli.