has been identified as an orphan antibiotic with high potential value in order to be investigated in this era of antibiotic resistance.13 No studies have been found on fosfomycin for the proposed or similar indica- tion in careful revision of the clinical trials public regis- tries. Therefore, an opportunity to design and conduct a randomised clinical trial to evaluate its efficacy and safety presented itself. In this sense, it seems especially important to take into consideration the new proposed paradigms for investigating new alternatives for
antibiotic resistant bacteria through randomised clinical trial designs in order to meet the real clinical needs.14 15 The main concern with the use of fosfomycin is the possibility of resistance development during treatment. While it is true that spread of resistant strains in our environment has been linked to increased consumption of drugs for oral treatment of uncomplicated UTI,16 it seems that the resilience of fosfomycin-resistant enter- obacteria has decreased, which would otherwise have permitted it to maintain its activity over time.17 Even though development of resistance to fosfomycin can occur during treatment, it seems to be much less fre- quent in E. coli than in Klebsiella spp or Pseudomonas aeru- ginosa, and specifically in UTI,17 which provides an adequate background for testing the efficacy of this drug in monotherapy for bacteraemic UTI caused by ESBL-EC. Also, bacteraemic infections with a source in the urinary tract, especially in the absence of urine obstruction, is associated with lower mortality in com- parison with other sources;18 finally, the development of resistance in the course of treatment is less likely in these infections.17 Therefore, the investigation of fosfo- mycin efficacy as monotherapy in bacteraemic UTIs by E. coli, at least if there has been an adequate source
control if necessary, is justified.
The few pharmacokinetic and pharmacodynamic
studies performed to date with fosfomycin indicate that sufficient plasma concentrations are reached for the treatment of systemic infections due to susceptible organ- isms for at least 4 h19 20 following an intravenous dose of 4 g. Since it is excreted unchanged in the urine, its levels in the urine are also suitable for diagnosing these infec- tions.19 Pharmacokinetic data available to date have been obtained following administration of single doses;21 however, we intend to determine fosfomycin plasma levels following repeated doses (48 h after treatment).
The Food and Drug Administration (FDA) considers ‘complicated UTI’ to be a syndrome for new therapy evaluation.22 However, we believe the syndrome defin- ition of the FDA is overly heterogeneous as it includes different clinical situations, from lower UTI in cathe- terised patients, to pyelonephritis with bloodstream infection in patients with structural of functional pro- blems in the urinary tract. The research group respon- sible for this trial considers that using such definitions for investigating fosfomycin would not provide valuable results, particularly for patients with bacteraemia; fur- thermore, the results can be readily transferable to non- bacteraemic UTIs. This is why we decided to include patients with BUTI, who are readily identifiable and for whom clinical decisions are taken every day in real practice.
We decided to use meropenem as comparator because carbapenems are considered the drugs of choice for inva- sive infections caused by ESBL producers,23 and there is extensive experience with meropenem. Ertapenem was not considered because treatment of UTIs is not an approved indication for this drug in Europe.24