Avibactam Synthesis

The emergence of inhibitor-resistant bacterial strains and also inefficient inhibitory activity of traditional β-lactam inhibitors against KPC enzyme, is inspiring the development of a variety of new non-β-lactam\β-lactamase inhibitors. The search for such inhibitors was started with the hope of preserving β-lactam activity.
4.1 Avibactam (NXL104)
Avibactam is a novel, covalent, reversible β-lactamase inhibitor with more potent and broader spectrum of activity (relative to clavulanic acid, sulbactam and tazobactam) against ESBL, AmpC, KPC as well as some class D enzymes which are resistant to inhibition by currently available β-lactam/β-lactamase inhibitors (Fig.1) (7, 56-58). This synthetic inhibitor has little intrinsic antibacterial activity

It has been paired with two of third-generation cephalosporins, ceftazidime and ceftaroline. Ceftazidime alone is hydrolyzed by KPC enzyme, ESBLs and class C enzymes, but avibactam restores the antibacterial activity and also susceptibility of ceftazidime(60). Several studies were conducted to evaluate ceftazidime-avibactam combination. Data showed that this combination has better inhibitory activity than ceftazidime alone and is a valuable alternative to overcome Gram-negative bacilli including Enterobacteriacae, K.pneumoniae, E.cloacae and Burkholderia cefacian that produce class A carbapenemases and also majority of OXA-48 group of carbapenemases (61-66). However, ceftazidime-avibactam resistance have been demonstrated from KPC-2 variants such as KPC-3 producer Enterobacteriacae including K.pneumoniae and E.cloacae(67-69). Among β-lactamases, KPC-2 slowly hydrolyze avibactam(57, 68). Ceftazidime-avibactam has no activity against MBLs but because monobactams are not hydrolyzed by MBLs, aztreonam-avibactam combination is effective in vitro against MBL-producing Enterobacteriacae, especially NDM-producers that coproduce ESBLs or AmpC enzymes (56,

Data from in vitro study has demonstrated that relebactam /imipenem combination is synergistic and shows considerably reduced MIC in imipenem-resistant isolates of KPC-producing K.pneumoniae and Pseudomonas strain (81-83). In a study that was conducted to evaluate the efficacy of relebactam-imipenem combination, relebactam restored 97% susceptibility of imipenem against KPC-producer K.pneumoniae isolates(84). Although MBLs(IMP, NDM, VIM) are not susceptible to relebactam /imipenem, OXA-48 producing Enterobacteriacae are weakly affected by this combination(70, 85). Due to greater potency of imipenem relative to cephalosporins, relebactam /imipenem combination is a better choice than ceftazidime-avibactam and ceftaroline-avibactam