Guidelines for Interpretation Required.
by Dr. med. Jennifer Kranz, Dr. Stefanie Schmidt, Dr. Cordula Lebert, Dr. med. Laila Schneidewind, PD Dr. med. Guido Schmiemann,
and Prof. Dr. med. Florian Wagenlehner in issue 50/2017
The new S3 guideline emphasizes the importance of pivmecillinam and nitroxolin in the empirical treatment of uncomplicated cystitis (1). We welcome this recommendation because both substances are effective for a relevant range of pathogens, have very good pharmacodynamics and pharmacokinetics, and can contribute to reducing resistance selection pressure. However, diagnostic-clinical microbiology is faced with a dilemma, because clinical thresholds to interpret resistance tests for these substances are available to a limited degree only. The CLSI guideline includes only breakpoints for mecillinam (the active substance of the prodrug pivmecillinam) for testing for Escherichia coli (2). EUCAST, however, provides breakpoints for mecillinam for testing for E coli, Klebsiella sp, and Proteus mirabilis. EUCAST breakpoints for nitroxoline currently exist only for E coli (3). Other pathogens of urinary tract infections (for example, Enterobacter sp, Citrobacter sp, Staphylococcus sp, and Enterococcus sp) have not been considered. The problem is aggravated by the fact that mecillinam and nitroxoline are—with one exception—not included in the standard test panels of automated sensitivity testing.
As a result, mecillinam and nitroxoline can be tested to a restricted degree only, and microbiological laboratories can therefore provide only inadequate support to clinicians in terms of the targeted treatment of cystitis with pivmecillinam or nitroxoline.
This dilemma can be resolved in future only if interpretation guidelines are implemented for resistance testing of mecillinam and nitroxoline to all relevant pathogens, and if these substances are included in commercial test panels for automated resistance testing. It would be highly desirable for the German national antimicrobial susceptibility testing committee (NAK, www.nak-deutschland.org) to come up with suggestions for how to deal with lacking thresholds until international regulations become available.
Prof. Dr. med. Frieder Schaumburg
Prof. Dr. med. Karsten Becker
Institut für Medizinische Mikrobiologie
Prof. Dr. Sören G. Gatermann
Institut für Hygiene und Mikrobiologie
Conflict of interest statement
Professor Gatermann has received honoraria for preparing scientific conferences and physical resources for a research project of Beckman Coulter and bioMérioux that he initiated.
Professor Schaumburg and Professor Becker declare that no conflict of interest exists.