Effects of combination of benzylpenicillin and fosfomycin on penicillin-resistant Streptococcus pneumoniae

Fosfomycin as Partner Drug for Systemic Infection Management. A Systematic Review of Its Synergistic Properties from In Vitro and In Vivo Studies

Fosfomycin is being increasingly prescribed for multidrug-resistant bacterial infections. In patients with systemic involvement, intravenous fosfomycin is usually administered as a partner drug, as part of an antibiotic regimen. Hence, the knowledge of fosfomycin pharmacodynamic interactions (synergistic, additive, indifferent and antagonistic effect) is fundamental for a proper clinical management of severe bacterial infections. We performed a systematic review to point out fosfomycin’s synergistic properties, when administered with other antibiotics, in order to help clinicians to maximize drug efficacy optimizing its use in clinical practice. Interactions were more frequently additive or indifferent (65.4%). Synergism accounted for 33.7% of total interactions, while antagonism occurred sporadically (0.9%). Clinically significant synergistic interactions were mostly distributed in combination with penicillins (51%), carbapenems (43%), chloramphenicol (39%) and cephalosporins (33%) in Enterobactaerales; with linezolid (74%), tetracyclines (72%) and daptomycin (56%) in Staphylococcus aureus; with chloramphenicol (53%), aminoglycosides (43%) and cephalosporins (36%) against Pseudomonas aeruginosa; with daptomycin (97%) in Enterococcus spp. and with sulbactam (75%) and penicillins (60%) and in Acinetobacter spp. fosfomycin-based antibiotic associations benefit from increase in the bactericidal effect and prevention of antimicrobial resistances. Taken together, the presence of synergistic interactions and the nearly total absence of antagonisms, make fosfomycin a good partner drug in clinical practice.

In vitro synergy testing of novel antimicrobial combination therapies against Neisseria gonorrhoeae

BACKGROUND

Antimicrobial-resistant Neisseria gonorrhoeae is a major public health threat. Current CDC treatment guidelines for uncomplicated gonorrhoea recommend only ceftriaxone plus either azithromycin or doxycycline. Additional treatment options are needed.

METHODS

We used antibiotic gradient synergy testing (the Etest) to evaluate antimicrobial combinations that included a third-generation cephalosporin (cefixime or ceftriaxone) plus azithromycin, doxycycline, gentamicin, rifampicin or fosfomycin. We tested each combination against 28 clinical N. gonorrhoeae isolates and four control strains of varying susceptibility profiles, and compared the results with those obtained using combination antimicrobial testing using agar dilution. We calculated the fractional inhibitory concentration index (FICI) for each combination to determine synergy, the results being interpreted as follows: FICI ≤ 0.5 = synergy; FICI > 4.0 = antagonism; and FICI > 0.5-4 = indifference.

RESULTS

The combinations of a third-generation cephalosporin plus azithromycin, doxycycline, rifampicin, gentamicin or fosfomycin produced FICIs of indifference. The Etest and agar dilution methods produced comparable results.

CONCLUSIONS

Combinations of ceftriaxone plus rifampicin, gentamicin or fosfomycin may warrant further clinical investigation as treatments for gonorrhoea. Using the Etest for synergy testing is a viable method that has practical advantages over agar dilution.

In vitro synergism of fosfomycin and clarithromycin antimicrobials against methicillin-resistant Staphylococcus pseudintermedius

BACKGROUND

Bacterial biofilms are of tremendous concern for clinicians, as they can compromise the ability of the immune system and antimicrobial therapy to resolve chronic and recurrent infections. Novel antimicrobial therapies or combinations targeted against biofilm establishment and growth subsequently represent a promising new option for the treatment of chronic infectious diseases. In this study, we treated bacterial biofilms produced by methicillin-resistant Staphylococcus pseudintermedius (MRSP) with a combination of fosfomycin and clarithromycin. We selected these agents, because they prevent biofilm formation and induce antimicrobial synergism that may also target other staphylococci.

RESULTS

We determined that the combination of fosfomycin and clarithromycin better impairs S. pseudintermedius biofilm formation compared to treatment with either therapy alone (P < 0.05). Morphological examination of these biofilms via scanning electron microscopy demonstrated that fosfomycin alone does impact biofilm formation on orthopaedic implants. However, this activity is enhanced in the presence of clarithromycin. We propose that the bacteriostatic activity of clarithromycin is accentuated when fosfoymcin is present, as it may allow better penetration into the biofilm matrix, allowing fosfomycin access to sessile bacteria near the surface of attachment.

CONCLUSIONS

Here, we demonstrate that the combination of fosfomycin and clarithromycin may be a useful therapy that could improve the clinical outcomes of treating antimicrobial resistant MRSP biofilms.

Heteroresistance to fosfomycin is predominant in Streptococcus pneumoniae and depends on the murA1 gene

Fosfomycin targets the first step of peptidoglycan biosynthesis in Streptococcus pneumoniae catalyzed by UDP-N-acetylglucosamine enolpyruvyltransferase (MurA1). We investigated whether heteroresistance to fosfomycin occurs in S. pneumoniae. We found that of 11 strains tested, all but 1 (Hungary(19A)) displayed heteroresistance and that deletion of murA1 abolished heteroresistance. Hungary(19A) differs from the other strains by a single amino acid substitution in MurA1 (Ala(364)Thr). To test whether this substitution is responsible for the lack of heteroresistance, it was introduced into strain D39. The heteroresistance phenotype of strain D39 was not changed. Furthermore, no relevant structural differences between the MurA1 crystal structures of heteroresistant strain D39 and nonheteroresistant strain Hungary(19A) were found. Our results reveal that heteroresistance to fosfomycin is the predominant phenotype of S. pneumoniae and that MurA1 is required for heteroresistance to fosfomycin but is not the only factor involved. The findings provide a caveat for any future use of fosfomycin in the treatment of pneumococcal infections.

Fosfomycin for the treatment of infections caused by Gram-positive cocci with advanced antimicrobial drug resistance: a review of microbiological, animal and clinical studies

BACKGROUND

The advancing antimicrobial drug resistance in Gram-positive cocci complicates the selection of appropriate therapy. The re-evaluation of older antibiotics may prove useful in expanding relevant therapeutic options.

OBJECTIVE

We sought to evaluate fosfomycin for the treatment of infections caused by methicillin-resistant staphylococci, vancomycin-resistant enterococci, and penicillin-non-susceptible pneumococci.

METHODS

We searched in PubMed, Scopus, and the Cochrane Library for studies evaluating the antimicrobial activity of fosfomycin against the above-mentioned pathogens, or the in vivo or clinical effectiveness of fosfomycin for the treatment of infections caused by these pathogens.

RESULTS/CONCLUSIONS

As reported in the identified studies, the susceptibility rate of methicillin-resistant Staphylococcus aureus to fosfomycin was > or = 90% in 12/22, and 50-90% in 7/22 studies; the cumulative susceptibility rate was 87.9% (4240/4892 isolates). The cumulative susceptibility rate of vancomycin-resistant enterococci to fosfomycin was 30.3% (183/604 isolates), and that of penicillin-non-susceptible pneumococci was 87.2% (191/219 isolates). Clinical data show that fosfomycin, primarily in combination regimens, has been associated with clinical success in 28/29 (96.6%) cases of infection (mainly pneumonia, bacteremia, and meningitis) by fosfomycin-susceptible isolates of methicillin-resistant S. aureus. The above data support further research on the role of fosfomycin against infections caused by Gram-positive cocci with advanced antimicrobial drug resistance.

Synergy of fosfomycin with other antibiotics for Gram-positive and Gram-negative bacteria

BACKGROUND

The alarming increase in drug resistance and decreased production of new antibiotics necessitate the evaluation of combinations of existing antibiotics. Fosfomycin shows no cross-resistance to other antibiotic classes. Thus, its combination with other antibiotics may potentially show synergy against resistant bacteria.

OBJECTIVE

To evaluate the available published evidence regarding the in vitro synergistic activity of fosfomycin with other antibiotic agents against Gram-positive and Gram-negative bacteria.

METHODS

PubMed and the Cochrane Library were searched.

RESULTS

Forty-one studies, including 34 (82.9%) conducted/published before 2000, were eligible for inclusion. The relatively limited number of isolates examined and the considerable heterogeneity of the retrieved studies regarding the definitions of synergy and the methodologies used hamper conclusive remarks for specific combinations of fosfomycin with other antibiotics. Yet, in the 27 studies providing data for Gram-positive strains (16 for Staphylococcus aureus, 3 for coagulase-negative staphylococci, 5 for Streptococcus pneumoniae, and 3 for Enterococcus spp.), fosfomycin showed synergy against methicillin-resistant Staphylococcus aureus when combined with cefamandole, cephazolin, ceftriaxone, ciprofloxacin, imipenem, and rifampicin. Data regarding Gram-negative strains reported from 15 studies (12 exclusively for P. aeruginosa, 2 exclusively for Enterobacteriaceae, 1 for both, and 1 for Acinetobacter baumannii) suggested that fosfomycin showed an estimable synergistic effect with gentamicin, amikacin, ceftazidime, cefepime, ciprofloxacin, levofloxacin, and aztreonam against P. aeruginosa.

CONCLUSIONS

The synergistic combination of fosfomycin with other antibiotics may be a useful alternative treatment option for Gram-negative and Gram-positive infections. Additional studies using more stringent definitions of synergy, and studies reporting on the clinical efficacy of fosfomycin combinations in the current era of high antimicrobial resistance are needed.

Clinical significance of the pharmacokinetic and pharmacodynamic characteristics of fosfomycin for the treatment of patients with systemic infections

The advancing antimicrobial drug resistance in common bacterial pathogens, along with the relative shortage of new antibacterial agents, call for the re-evaluation of available therapeutic options. Fosfomycin is an established treatment option for uncomplicated urinary tract infections. Here we review and evaluate the main pharmacokinetic and pharmacodynamic parameters of intravenously administered fosfomycin with regard to its use for systemic infections. Fosfomycin is a relatively small, hydrophilic agent with almost negligible serum protein binding. It is excreted unchanged in urine, achieving high concentrations for a prolonged period. Fosfomycin has good distribution into tissues, achieving clinically relevant concentrations in sites such as serum, soft tissue, lungs, bone, cerebrospinal fluid and heart valves. Fosfomycin has shown antimicrobial activity against biofilms, particularly in combination with fluoroquinolones. It also exerts immunomodulatory effects, mainly on lymphocyte and neutrophil function. Potentially useful properties of fosfomycin regarding its use in combination regimens include reduction in the expression of certain penicillin-binding proteins and attenuation of nephrotoxicity caused by several antimicrobial agents. In conclusion, the pharmacokinetic and pharmacodynamic properties of fosfomycin do not preclude its use for various types of systemic infections and suggest further research on relevant clinical applications of this agent.