fThe antileprosy drug clofazimine has shown potential for shortening tuberculosis treatment; however, the current dosing of the drug is not evidence based, and the optimal dosing is unknown. Our objective was to conduct a preclinical evaluation of the pharmacokinetics and pharmacodynamics of clofazimine in the mouse model of tuberculosis, with the goal of providing useful information on dosing for future studies. Pharmacokinetic parameters were evaluated in infected and uninfected BALB/c mice. Pharmacodynamic parameters were evaluated in Mycobacterium tuberculosis-infected mice that were treated for 12 weeks with one of six different clofazimine dosing regimens, i.e., doses of 6.25, 12.5, and 25 mg/kg of body weight/day and 3 regimens with loading doses. Clofazimine progressively accumulated in the lungs, livers, and spleens of the mice, reaching levels of greater than 50 g/g in all tissues by 4 weeks of administration, while serum drug levels remained low at 1 to 2 g/ml. Elimination of clofazimine was extremely slow, and the half-life was dependent on the duration of drug administration. Clofazimine exhibited dosedependent tissue and serum concentrations. At any dose, clofazimine did not have bactericidal activity during the first 2 weeks of administration but subsequently demonstrated potent, dose-independent bactericidal activity. The antituberculosis activity of clofazimine was dependent on neither the dose administered nor the drug concentrations in the tissues, suggesting that much lower doses could be effectively used for tuberculosis treatment. C lofazimine (CFZ) is a phenazine dye developed in the 1950s for the treatment of tuberculosis (TB) (1, 2). Despite promising activity against Mycobacterium tuberculosis both in vitro and in vivo, clofazimine was not advanced as a TB drug but instead became incorporated decades later into the multidrug treatment of leprosy, where it remains a key drug (3, 4). Interest in clofazimine for TB treatment has been revitalized following the 2010 report by Van Deun and colleagues that a clofazimine-containing regimen not only was highly effective for the treatment of multidrug-resistant (MDR) TB, but was also associated with a significantly decreased duration of therapy (5); 9 months of a clofazimine-containing regimen resulted in 87.9% relapse-free cure, which is in sharp contrast to the limited efficacy (less than 50% relapse-free cure) of the World Health Organization (WHO)-recommended, at least 20-month-long MDR-TB treatment regimen (6, 7). This report was complemented by experimental chemotherapy studies in which the inclusion of clofazimine in first-and secondline regimens significantly shortened the duration of treatment needed for relapse-free cure in mouse models of drug-susceptible and MDR TB, respectively (8, 9). These clinical and preclinical data suggest that clofazimine has great potential for TB treatment.Because clofazimine was abandoned as an option for TB treatment shortly after its discovery, and also because the use of clofazimine for leprosy is not ba...

SummaryA literature review was undertaken to ascertain the molecular basis for tigecycline and colistin resistance mechanisms and the experimental basis for the detection and delineation of this resistance particularly in carbapenemaseproducing Gram-negative bacteria. Pubmed, Google Scholar and Science Direct were searched with the keywords colistin, tigecycline, resistance mechanisms and detection methods. Trans-complementation and comparative MIC studies, mass spectrometry, chromatography, spectrofluorometry, PCR, qRT-PCR and whole genome sequencing (WGS) were commonly used to determine tigecycline and colistin resistance mechanisms, specifically modifications in the structural and regulatory efflux (acrAB, OqxAB, kpgABC adeABC-FGH-IJK, mexAB-XY-oprJM and soxS, rarA robA, ramRAB marRABC, adeLRS, mexRZ and nfxb) and lipid A (pmrHFIJFKLM, lpxA, lpxC lpxD and mgrB, pmrAB, phoPQ,) genes respectively. Mutations in the ribosomal 16S rRNA operon rrnBC, also yielded resistance to tigecycline through target site modifications. The mcr-1 gene conferring resistance to colistin was identified via WGS, transcomplementation and a murine thigh infection model studies. Common detection methods are mainly antibiotic sensitivity testing with broth microdilution while molecular identification tools are mostly PCR and WGS. Spectrofluorometry, MALDI-TOF MS, micro-array and real-time multiplex PCR hold much promise for the future as new detection tools.

The worldwide proliferation of life-threatening metallo-β-lactamase (MBL)-producing Gram-negative bacteria is a serious concern to public health. MBLs are compromising the therapeutic efficacies of β-lactams, particularly carbapenems, which are last-resort antibiotics indicated for various multidrug-resistant bacterial infections. Inhibition of enzymes mediating antibiotic resistance in bacteria is one of the major promising means for overcoming bacterial resistance. Compounds having potential MBL-inhibitory activity have been reported, but none are currently under clinical trials. The need for developing safe and efficient MBL inhibitors (MBLIs) is obvious, particularly with the continuous spread of MBLs worldwide. In this review, the emergence and escalation of MBLs in Gram-negative bacteria are discussed. The relationships between different class B β-lactamases identified up to 2017 are represented by a phylogenetic tree and summarized. In addition, approved and/or clinical-phase serine β-lactamase inhibitors are recapitulated to reflect the successful advances made in developing class A β-lactamase inhibitors. Reported MBLIs, their inhibitory properties, and their purported modes of inhibition are delineated. Insights into structural variations of MBLs and the challenges involved in developing potent MBLIs are also elucidated and discussed. Currently, natural products and MBL-resistant β-lactam analogues are the most promising agents that can become clinically efficient MBLIs. A deeper comprehension of the mechanisms of action and activity spectra of the various MBLs and their inhibitors will serve as a bedrock for further investigations that can result in clinically useful MBLIs to curb this global menace.

Our data suggest that clofazimine's delayed antimicrobial activity may be due more to its mechanism of action rather than to host-related factors.

No abstract