Glenn S. Tillotson

Discovery research: the scientific challenge of finding new antibiotics

The dwindling supply of new antibiotics largely reflects regulatory and commercial challenges, but also a failure of discovery. In the 1990s the pharmaceutical industry abandoned its classical ways of seeking antibiotics and instead adopted a strategy that combined genomics with high-throughput screening of existing compound libraries. Too much emphasis was placed on identifying targets and molecules that bound to them, and too little emphasis was placed on the ability of these molecules to permeate bacteria, evade efflux and avoid mutational resistance; moreover, the compound libraries were systematically biased against antibiotics. The sorry result is that no antibiotic found by this strategy has yet entered clinical use and many major pharmaceutical companies have abandoned antibiotic discovery. Although a raft of start-up companies-variously financed by venture capital, charity or public money--are now finding new antibiotic compounds (some of them very promising in vitro or in early trials), their development through Phase III depends on financial commitments from large pharmaceutical companies, where the discouraging regulatory environment and the poor likely return on investment remain paramount issues.

Anti-infective research and development—problems, challenges, and solutions

In communities and hospitals around the world, the number of patients with antibiotic-resistant infections continues to climb. Our current armamentarium of drugs are gradually becoming ineffective and a new pipeline of robust compounds is needed urgently. In this Forum, we present several perspectives on the problems and pitfalls of drug discovery and development, the challenges faced by the practising physician, and potential solutions to protecting and safeguarding the public health of future generations.

The urgent need for new antibacterial agents

I find it continually amazing that society as a whole does not recognize the consequences of rising antimicrobial resistance as the threat it most certainly is. This is not for a lack of sustained activity by those who share these concerns. Far from it. Since 1997 there have been a plethora of enquiries, reports and recommendations—many from important bodies in both Europe and North America, yet little meaningful action has materialized. Some might consider this to be rather negative and an overstatement, yet can they point out a concrete outcome to all this activity? I like to think that the UK has led the way in raising concerns that antibiotic use, especially overuse (in animals as well as man) will hasten the day when these essential agents will lose their efficacy. The Swann Committee first brought this to our attention in 1969, and in 1998 a House of Lords report starkly stated that antimicrobial resistance was a ‘major threat to public health’. Most recently, the Infectious Diseases Society of America (IDSA) and the European Union, among others, have voiced their concerns. In 2009 the WHO called antibiotic resistance one of the three greatest threats to human health, and in 2011 the focus of World Health Day was ‘Combating Antibiotic Resistance’. However, antimicrobial resistance moves on in an inexorable fashion and the prospects for new agents are as bleak as ever. Perhaps it is us, the health professionals, who are at fault, either in the nature of our message, or in approaching the wrong groups who cannot influence outcomes? The BSAC has changed tack in its report on ‘The Urgent Need’, as outlined in the articles accompanying this one. – 9 Rather than restate the concerns surrounding antimicrobial resistance, its surveillance and how it might be contained (or more accurately, how its progress might be slowed), the BSAC adopted a different approach, focusing on the barriers to discovery and development of new technologies that might combat resistance (including new antimicrobial agents) and how these might be overcome. The Working Party of the BSAC examined three areas, namely research, regulation and economics. While recognizing that these areas are not distinct and there is much important overlap, the Working Party was challenged to suggest a practical framework for action. Critically there was an awareness on the part of the Working Party that the BSAC cannot undertake this immense task on its own, and co-operation with others is key. I do not wish to précis the report here, but rather make some personal comments on what I consider to be a few important areas. In research there is a major concern that international expertise in natural product discovery is being rapidly lost—how long has it been since such an antibacterial compound has been marketed? Overoptimism in genomics and highthroughput screening as the answer to the discovery of new agents in the 1990s would appear to have put back the cause by at least a decade. Research into how to influence the public’s perceptions of the risks confronting them (hence the political response) is also needed. Most certainly the regulatory issues relating to the licensing of new antimicrobials are extremely important. The bureaucrats are risk averse, yet do not take account of the risks to society of their inaction. This would change if political concerns were more loudly voiced. It is my personal opinion that it is changes in the economic field that are most likely to yield results. We were not the first to expound the economic arguments. Everything the Working Party heard from industry makes me believe that the marketplace must change. A course of antibiotics costs a few pounds or dollars and can save lives. In hospital practice we shudder if the costs rise into the hundreds. The angiogenesis inhibitor bevacizumab (trade name Avastin) is one of the most expensive widely marketed drugs. In 2008 sales generated nearly US

Susceptibility of Staphylococcus aureus isolated from skin and wound infections in the United States 2005–07: laboratory-based surveillance study

2.7 billion for Genentech, yet it has only modest effects on patient survival in a number of cancers. This is not to say it should not be used, but rather that there should be a rebalancing of risks and, more importantly, benefits. I would suggest that antimicrobials (other than a few antifungals) should be at a higher premium. Antimicrobial development must allow pharmaceutical companies realistic returns on their investment. This is crucial if society is to obtain new agents. So what actions should the BSAC undertake? The Working Party has suggested a number of short-, mediumand long-term activities. These, realistically, revolve around communication, in its broadest sense, with clinicians and academics, but possibly more importantly, with opinion formers in the UK and further afield. Such a programme of work, which will not be cheap, should include other parties and could usefully include the participation of the pharmaceutical industry.

MICs, MPCs and PK/PDs: a match (sometimes) made in hosts

OBJECTIVES The aim of this study was to describe the rates of antimicrobial susceptibility of Staphylococcus aureus from skin and wound infections reported from nine regions of the USA during 2005-07 and to identify the regional variation in patterns of resistance. METHODS The Surveillance Network (TSN) comprises 296 laboratories across the nine census regions of the USA. TSN laboratories reported the susceptibility data for six antimicrobials by isolate with source and other relevant data. Antimicrobial susceptibility data were analysed by individual drug resistance, multidrug resistance and geographical distribution of resistance phenotypes. RESULTS There were over 380 000 isolates of S. aureus tested and reported for the period 2005-07. Methicillin resistance was observed in 57.8% in 2007, with little change from 2005. There was little difference in rates of methicillin resistance between community and hospital strains, although strains from intensive care units (ICUs) tended to be slightly more resistant overall. Resistance to other antimicrobials was also reported. A regional variation in resistance rates was noted with the highest rates in the Central states and lowest in the New England and Mid-Atlantic regions. There was high activity observed with trimethoprim/sulfamethoxazole and gentamicin. Linezolid resistance was rare. Oxacillin resistance was similar among paediatric and elderly cohorts, whereas ciprofloxacin and clindamycin resistance was significantly (P < 0.01) more common in elderly patients when compared with both paediatric and adult populations. Less than a third of all isolates showed no resistance mechanism, 30.3%. Three distinct resistance phenotypes accounted for 46% of all resistant strains. Overall, there were more highly drug-resistant isolates from the ICU with four, five or six drug-resistant phenotypes accounting for over a third of all strains. CONCLUSIONS S. aureus has become methicillin-resistant in both the community and hospital settings; however, little change has been seen in the past 3 years. Multiresistant strains now are seen in all settings, but due to regional variation, empirical therapy should be guided by local susceptibility patterns. Currently, among the agents studied, only trimethoprim/sulfamethoxazole, gentamicin and linezolid exhibit susceptibility rates of >95%.

New and alternative approaches to tackling antibiotic resistance

There is little doubt that we have a global pandemic of antimicrobial-resistant microorganisms. Despite regional variations in resistance rates for various bacteria/drug combinations, the overall impact of this trend has impacted on individual patients and the economics of managing infections, as well as our approach to the empirical use of antimicrobial compounds for both inand outpatient management. Indeed, various treatment guidelines from expert working groups recommend different treatment options based on the likelihood of resistant pathogens. Currently, antibiotics are approved based on the demonstration of noninferiority of a new drug when compared with a standard antibiotic agent already approved for a specific indication. However, such trials may fail to take into account various microbiological or pharmacological parameters that could be used to determine optimal versus suboptimal dosing. As such, these parameters may not necessarily affect clinical outcome but may have a huge impact on the selection of drug-resistant pathogens.

Clinical Trial Design for Mild-to-Moderate Community-Acquired Pneumonia—An Industry Perspective

Multidrug-resistant bacteria are becoming more common and due to their multiplicity of mechanisms, they are frequently resistant to many if not all of the current antibiotics. This daunting spectre has been the target of many research efforts into conventional antibiotics and alternative approaches. This review focuses on the more recent advances in these fields with an overview on peptidomimetics, nanoparticles and their derivatives, FimH inhibitors, quorum sensing inhibition molecules, neoglycosides and phage therapies. These various approaches are at different stages of development, some are closer to the clinic than others, but recent regulatory guidance and re-awakened interest from the pharmaceutical companies gives us some optimism for the future.

Vancomycin for Staphylococcus aureus therapy of respiratory tract infections: the end of an era?

The use of noninferiority clinical trials is problematic unless one can establish the benefit of the active control versus no treatment. In community-acquired pneumonia, there are no placebo-controlled clinical trials establishing the benefit of antibiotic treatment, because the observed benefit of sulfapyridine and, subsequently, penicillin was established before the advent of randomized clinical studies. Historical data and observational cohort studies have established the marked decrease in mortality resulting from antimicrobial therapy; however, mortality is not a suitable end point for contemporary clinical trials for mild-to-moderate community-acquired pneumonia that is treated with oral antimicrobial drugs in ambulatory patients. There are historical clinical data that describe the timing of spontaneous recovery in patients with documented pneumonia caused by Streptococcus pneumoniae. In addition, there is one contemporary clinical trial that demonstrated superiority in clinical response of levofloxacin versus a cephalosporin regimen of ceftriaxone and/or cefuroxime for treatment of mild-to-moderate community-acquired pneumonia. Using either the historical data or the superiority study of levofloxacin, one can justify a noninferiority margin of 10% for the per-protocol population and 15% for the microbiologically evaluable population for future noninferiority clinical trials for mild-to-moderate community-acquired pneumonia.

Efficacy and safety of ridinilazole compared with vancomycin for the treatment of Clostridium difficile infection: a phase 2, randomised, double-blind, active-controlled, non-inferiority study

In 1991, Karchmer [1] raised several key issues related to the pathogenesis and optimal treatment of Staphylococcus aureus infections. The main issue concerned the role of vancomycin in treating serious or invasive methicillin-sensitive S. aureus ( MSSA) and methicillinresistant S. aureus (MRSA) infections. He recognized and envisaged the current global epidemic of MRSA infections in hospitals [2], and to a lesser extent the community [3], and concluded that ‘there is an urgent need for effective alternatives to vancomycin for the treatment of MRSA infections’. Since then we have emerging evidence, a recent meta-analysis, that in patients with S. aureus -related bacteraemia, MRSA is an independent risk factor for higher mortality compared with MSSA bacteraemia [4]. This adds further support to the ongoing debate about the virulence of MRSA infections compared with MSSA and the need for optimal antibiotics at the onset of treatment. The reality, a decade later, is the occurrence of a broad range of serious and invasive MRSA infections, often in vulnerable patients in ‘high risk’ clinical settings [5]. The need to treat many of these patients empirically with a view to ‘covering’ the most likely offending pathogens is perceived to be high if the critical therapeutic window of opportunity for optimal antibiotic therapy is not to be missed. The undesirable consequences of not getting the ‘right drug, to the right patient, in the right dose at the right time’ are clear [6]. The rapid laboratory and clinical capability of predicting patients likely to be infected with MRSA continues to improve but is by no means ideal [7,8]. Additionally, we are witnessing the concurrent rise in S. aureus strains that exhibits glycopeptide-intermediate susceptibility from several countries including Japan, France and US that has been subject to recent review [9]. For example, strains with MIC to vancomycin of 4 mg/l have caused clinical infections that failed to respond to vancomycin therapy. Traditionally, when the effectiveness of an antimicrobial agent in serious infections is considered, there has been an overemphasis on the need for bactericidal activity as a pre-requisite for a good outcome. Many of us now accept that local tissue penetration should be considered of equal importance. This is particularly important when looking at treatment options for staphylococcal infections, especially in tissues such as lung or the endovascular lining. Vancomycin is still regarded as the ‘gold-standard’ therapy for serious or invasive MRSA infections. Considering Karchmer’s concerns of a decade ago, we examine what more have we learnt about vancomycin treatment and summarize the emerging evidence for new or combination therapies. Vancomycin is bactericidal and appears to exert its effect by binding to the precursor units of peptidoglycan synthesis inhibiting the transpeptidase reaction. It exhibits concentration-independent bactericidal action against susceptible bacteria and is more bactericidal in aerobic conditions. This effect is exerted without a lag period but acts only on multiplying organisms and with a post-antibiotic effect of about 2 h. Against MSSA, it is a less active agent than b-lactams [1,10 /12] by virtue of being more slowly and incompletely bactericidal compared with equivalent concentrations of a b-lactam. A recent illustration of this phenomenon in clinical practice was demonstrated by Tam et al. [13] in haemodialysis patients with MSSA bacteraemia. This study revealed that persistent bacteraemia 24 h after therapy was significantly greater (37% vs. 25%, P /0.05) in patients initially treated with vancomycin compared with those with a b-lactam. Additionally, in patients with MSSA endocarditis and related bacteraemia, there * Corresponding author. Tel.: /44-1382-660-111; fax: /44-1382816-178. E-mail address: dilip.nathwani@tuht.scot.nhs.uk (D. Nathwani). International Journal of Antimicrobial Agents 21 (2003) 521 /524

Clostridium difficile--a moving target.

Summary Background Clostridium difficile infection is the most common health-care-associated infection in the USA. We assessed the safety and efficacy of ridinilazole versus vancomycin for treatment of C difficile infection. Methods We did a phase 2, randomised, double-blind, active-controlled, non-inferiority study. Participants with signs and symptoms of C difficile infection and a positive diagnostic test result were recruited from 33 centres in the USA and Canada and randomly assigned (1:1) to receive oral ridinilazole (200 mg every 12 h) or oral vancomycin (125 mg every 6 h) for 10 days. The primary endpoint was achievement of a sustained clinical response, defined as clinical cure at the end of treatment and no recurrence within 30 days, which was used to establish non-inferiority (15% margin) of ridinilazole versus vancomycin. The primary efficacy analysis was done on a modified intention-to-treat population comprising all individuals with C difficile infection confirmed by the presence of free toxin in stool who were randomly assigned to receive one or more doses of the study drug. The study is registered with ClinicalTrials.gov, number NCT02092935. Findings Between June 26, 2014, and August 31, 2015, 100 patients were recruited; 50 were randomly assigned to receive ridinilazole and 50 to vancomycin. 16 patients did not complete the study, and 11 discontinued treatment early. The primary efficacy analysis included 69 patients (n=36 in the ridinilazole group; n=33 in the vancomycin group). 24 of 36 (66·7%) patients in the ridinilazole group versus 14 of 33 (42·4%) of those in the vancomycin group had a sustained clinical response (treatment difference 21·1%, 90% CI 3·1–39·1, p=0·0004), establishing the non-inferiority of ridinilazole and also showing statistical superiority at the 10% level. Ridinilazole was well tolerated, with an adverse event profile similar to that of vancomycin: 82% (41 of 50) of participants reported adverse events in the ridinilazole group and 80% (40 of 50) in the vancomycin group. There were no adverse events related to ridinilazole that led to discontinuation. Interpretation Ridinilazole is a targeted-spectrum antimicrobial that shows potential in treatment of initial C difficile infection and in providing sustained benefit through reduction in disease recurrence. Further clinical development is warranted. Funding Wellcome Trust and Summit Therapeutics.