Tuberculosis (TB) remains the top killer from an infectious globally causing an estimated 1.674.000 million deaths worldwide. In 2016, WHO estimates 600.000 cases of rifampicin-resistant TB of which 490.000 had multidrug-resistant (MDR) and less than half of them survive after receiving currently recommended WHO treatment regimens, illustrating weaknesses in current treatment approaches. We review progress and advances in the development of new and repurposed TB drugs, treatment trials and host-directed therapies. Updates are provided on phase 3 trials of the new compounds bedaquiline, delamanid, pretomanid; phase 2 trials of sutezolid, SQ-109, LCB01-0371, PBTZ-169; and five new drugs in phase 1 development. Approved or repurposed drugs undergoing further testing are rifampicin, rifapentine, clofazimine, and linezolid. Update on ongoing clinical trials, which aim to shorten TB treatment and improve treatment outcome is given. Several new or repurposed antimicrobial drugs are in advanced trial stages for MDR-TB, and five antimicrobial drug candidates are in phase 1 (Q203, TBI-166, OPC-167832, GSK 070, TBA-7371) and 5 in pre-clinical studies. Specific issues of safety and toxicity; drug-drug interactions; Therapeutic Drug Monitoring are reviewed. A wide range of candidate host-directed therapies (HDTs) and immune-based treatments are being investigated to accelerate the eradication of M.tb infection and for use as adjunctive therapy in shortening duration of treatment, preventing permanent lung injury and improving treatment outcomes of MDR-TB. Ongoing clinical trials of HDTs for TB treatment, the current HDT development pipeline and translational research efforts for advancing further HDT options are presented. Ongoing clinical trials of HDTs for TB treatment, the current HDT development pipeline and translational research efforts for advancing further HDT options are presented.5

Despite extensive global efforts in the fight against killer infectious diseases, they still cause one in four deaths worldwide and are important causes of long-term functional disability arising from tissue damage. The continuing epidemics of tuberculosis, HIV, malaria, and influenza, and the emergence of novel zoonotic pathogens represent major clinical management challenges worldwide. Newer approaches to improving treatment outcomes are needed to reduce the high morbidity and mortality caused by infectious diseases. Recent insights into pathogen-host interactions, pathogenesis, inflammatory pathways, and the host's innate and acquired immune responses are leading to identification and development of a wide range of host-directed therapies with different mechanisms of action. Host-directed therapeutic strategies are now becoming viable adjuncts to standard antimicrobial treatment. Host-directed therapies include commonly used drugs for non-communicable diseases with good safety profiles, immunomodulatory agents, biologics (eg monoclonal antibodies), nutritional products, and cellular therapy using the patient's own immune or bone marrow mesenchymal stromal cells. We discuss clinically relevant examples of progress in identifying host-directed therapies as adjunct treatment options for bacterial, viral, and parasitic infectious diseases.

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The first cases of totally drug-resistant (TDR) tuberculosis (TB) were reported in Italy 10 years ago; more recently, cases have also been reported in Iran, India and South Africa. Although there is no consensus on terminology, it is most commonly described as 'resistance to all first- and second-line drugs used to treat TB'. Mycobacterium tuberculosis (M.tb) acquires drug resistance mutations in a sequential fashion under suboptimal drug pressure due to monotherapy, inadequate dosing, treatment interruptions and drug interactions. The treatment of TDR-TB includes antibiotics with disputed or minimal effectiveness against M.tb, and the fatality rate is high. Comorbidities such as diabetes and infection with human immunodeficiency virus further impact on TB treatment options and survival rates. Several new drug candidates with novel modes of action are under late-stage clinical evaluation (e.g., delamanid, bedaquiline, SQ109 and sutezolid). 'Repurposed' antibiotics have also recently been included in the treatment of extensively drug resistant TB. However, because of mutations in M.tb, drugs will not provide a cure for TB in the long term. Adjunct TB therapies, including therapeutic vaccines, vitamin supplementation and/or repurposing of drugs targeting biologically and clinically relevant molecular pathways, may achieve better clinical outcomes in combination with standard chemotherapy. Here, we review broader perspectives of drug resistance in TB and potential adjunct treatment options.