SAN DIEGO — High cure rates can be achieved with fosfomycin in patients with chronic prostatitis — many of whom are resistant to the current first-line treatment of fluoroquinolones — according to results from a new study.

"For us, it's an alternative treatment," said lead researcher Ilias Karaiskos, MD, from the Hygeia General Hospital in Athens, Greece. "We believe that if we have quinolones we should use them because many studies show they are effective and have high levels in the prostate tissue."

"But if I have a patient who has a micro-organism that is resistant to quinolones, I give fosfomycin," he told Medscape Medical News.

The study results were presented here at the Interscience Conference of Antimicrobial Agents and Chemotherapy 2015.

Dr Karaiskos and his colleagues evaluated outpatients with chronic prostatitis treated at the infectious disease clinic of a tertiary hospital from November 2013 to March 2015. Mean age of the patients was 53.6 years.

Of the 20 outpatients, 65% were infected with Escherichia coli, 15% with Klebsiella oxytoca, 10% with Proteus mirabilis, and 10% with Enterococcus faecalis.

Of these, 75% were resistant to fluoroquinolones, but were all susceptible to fosfomycin, a drug approved to treat urinary tract infections in pregnant women.

When Quinolones Don't Work

"We are seeing resistance to quinolones." Dr Karaiskos explained. In fact, "rates are increasing around the world. We don't have many drugs that penetrate the prostate tissue, so we were looking for an alternative regimen that was cheap and easy to give without many side effects."

"Because we haven't used fosfomycin a lot, most pathogens are sensitive to it," he reported.

All patients received oral fosfomycin 3 g once daily during the first week of treatment and then every 48 hours for the subsequent 5 weeks.

"Our cure rate was 85%, based on resolution of clinical symptoms and the resolution of imaging abnormalities," Dr Karaiskos said. And cure was verified at 3 months with cultures and symptoms.

"To our knowledge," he said, this is "the largest series of patients treated successfully with oral fosfomycin once daily for a period of 6 weeks with a cure rate of 85%. The most common side effect was diarrhea, which usually subsided with prolongation of the dosage intervals."

"Chronic prostatitis is notorious for relapsing, so usually cure is defined after a long period of nonrelapse, for example, 6 months," said Lindsay Grayson, MD, from the University of Melbourne in Australia, who has been involved in a study of fosfomycin concentrations in the prostate of men with chronic prostatitis (Clin Infect Dis. 2014;58:e101-e105) and a report of two cases of cure with this drug (Clin Infect Dis. 2015;61:1141-1143).

The 48-hour dosing in this study "was lower than we use. We know from our patients that adequate trough levels — in serum at least — seem to require daily fosfomycin," said Dr Grayson.

"Of course, if 48-hourly works, that's great, since intraprostatic levels may be more sustained than the levels in serum. However, trough serum levels with daily dosing only just attained concentrations greater than the minimum inhibitory concentration of most E coli strains," he explained.

The study authors and Dr Grayson have disclosed no relevant financial relationships.

Interscience Conference of Antimicrobial Agents and Chemotherapy (ICAAC) 2015: Abstract L1253. Presented September 20, 2015.