What we may expect from novel antibacterial agents in the pipeline with respect to resistance and pharmacodynamic principles.

There are some 43 small molecules in the antibiotic development pipeline from late preclinical stage (7 compounds) through Phase 1 (11 molecules), Phase 2 (13 molecules) to Phase 3 (12 molecules). The majority of these are representatives of established antibiotic classes that have been modified to address problems of resistance. In addition, there is considerable activity around the discovery of novel classes of β-lactamase inhibitors with 10 combinations representing 4 inhibitor classes, at different stages of development. The combination of such inhibitors, which have broad activity against serine β-lactamases and may even inhibit some penicillin binding proteins, with carbapenems, cephalosporins or aztreonam, provides enhanced activity against multi-drug resistant Gram-negative bacteria. There are 6 molecules representing novel classes of antibiotics but only one of these, murepavadin, is expected to have activity against a Gram-negative pathogenic bacterium (Pseudomonas aeruginosa). Although the new analogues of existing classes, and novel combinations, have been designed to address specific resistance problems, it is by no means certain than they will not be affected by the general mechanisms of resistance, particularly decreased net flux across the Gram-negative outer membrane. The potential impact of resistance mechanisms on the new agents is assessed and the ways in which PK/PD studies are used to design dosing regimens for the new agents, especially combinations, as well as to improve dosing of existing antibiotics are discussed.