A 3 g dose of once-daily fosfomycin for 1 week followed by 3 g every 48 hours for 6 to 12 weeks is a safe and effective therapy for chronic bacterial prostatitis with minimal toxicity and can be recommended in cases of multi-drug resistant (MDR) pathogens, according to a study published in the Journal of Antimicrobial Chemotherapy.

As few antibiotics are able to reach a therapeutic concentration in the prostate, chronic bacterial prostatitis remains difficult to treat. This prospective, observational study was designed to evaluate the safety and efficacy of fosfomycin in the treatment of chronic bacterial prostatitis as a result of MDR pathogens. Patients (N=44) were started on a regimen of 3 g fosfomycin every 24 hours for 1 week, followed by 3 g every 48 hours for 6 weeks (n=25), which was extended to 12 weeks for patients with calcifications in the prostate (n=19). Primary outcomes were microbiologic and clinical cure rate at the end of treatment and rate of relapse at 3 months and 6 months.

The most prevalent pathogen was Escherichia coli at 66%, followed by Enterococcus faecalis and Klebsiella spp. at 14%. Of these strains, 59% were MDR, and 23% had an extended spectrum β-lactamase phenotype. Of the 44 bacterial strains identified and included in the study, 33 were resistant to fluoroquinolones, but all were shown to be susceptible to fosfomycin (median minimum inhibitory concentration for gram-negative pathogens 1.5 mg/L). The cure rate was 80% at 3 months, 73% at 6 months, and 82% at the end of treatment. At 6 months, microbiologic eradication was achieved in 77% of participants and in 86% at the end of treatment. Twelve patients experienced treatment failure, and the most common adverse event observed was diarrhea at 18%.

Study limitations included a small sample size with no control group and that the study was based at a single center. In addition, follow-up microbiologic evaluation was primarily based on urine cultures due to the difficulties in repeating a Meares-Stamey procedure, so the cure rates could have been overestimated.

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The study investigators concluded that using fosfomycin in this manner “was proven as a safe and effective therapy with minimal toxicity and could be recommended in case of bacterial resistance to fluoroquinolones or in case of poor tolerability of the first-line agent and whenever there is laboratory confirmation of susceptibility to fosfomycin.”

Reference

Karaiskos I, Galani L, Sakka V, et al. Oral fosfomycin for the treatment of chronic bacterial prostatitis [published online February 22, 2019]. J Antimicrob Chemother. doi: 10.1093/jac/dkz015