The emergence and spread of antimicrobial resistance in Neisseria gonorrhoeae is seriously threatening the treatment and control of
gonorrhea globally. Novel treatment options are essential, coupled with appropriate methods to pharmacodynamically examine the efficacy and resistance emergence of these novel drugs. Herein, we used our dynamic in vitro hollow fiber
infection model (HFIM) to evaluate
protein-unbound
lefamulin, a semisynthetic
pleuromutilin, against N. gonorrhoeae. Dose-range and dose-fractionation experiments with N. gonorrhoeae reference strains: WHO F (susceptible to all relevant antimicrobials), WHO X (extensively drug-resistant, including
ceftriaxone resistance), and WHO V (high-level
azithromycin resistant, and highest gonococcal MIC of
lefamulin (2 mg/l) reported), were performed to examine
lefamulin gonococcal killing and resistance development during treatment. The dose-range experiments, simulating a single oral dose of
lefamulin based on human plasma concentrations, indicated that ≥1.2 g, ≥2.8 g, and ≥9.6 g of
lefamulin were required to eradicate WHO F, X, and V, respectively. Dose-fractionation experiments, based on human
lefamulin plasma concentrations, showed that WHO X was eradicated with ≥2.8 g per day when administered as q12 h (1.4 g twice a day) and with ≥3.6 g per day when administered as q8 h (1.2 g thrice a day), both for 7 days. However, when simulating the treatment with 5-10 times higher concentrations of free
lefamulin in relevant
gonorrhea tissues (based on urogenital tissues in a rat model), 600 mg every 12 h for 5 days (approved oral treatment for community-acquired
bacterial pneumonia) eradicated all strains, and no
lefamulin resistance emerged in the successful treatment arms. In many arms failing single or multiple dose treatments for WHO X,
lefamulin-resistant mutants (MIC = 2 mg/l), containing an A132V amino acid substitution in
ribosomal protein L3, were selected. Nevertheless, these
lefamulin-resistant mutants demonstrated an impaired biofitness. In conclusion, a clinical study is warranted to elucidate the clinical potential of
lefamulin as a treatment option for uncomplicated
gonorrhea (as well as several other bacterial
STIs).