In vitro activity of a novel diaminopyrimidine compound, iclaprim, against Chlamydia trachomatis and C. pneumoniae

Randomized, double-blind, multicenter safety and efficacy study of rifalazil compared with azithromycin for treatment of uncomplicated genital Chlamydia trachomatis infection in women

A randomized, double-blind study comparing single-dose chlamydia therapies of oral rifalazil (25 mg) and azithromycin (1 g) was conducted in 82 women with uncomplicated genital Chlamydia trachomatis infection. The microbiologic cure rate of C. trachomatis with rifalazil (n = 33) was 84.8% at the visit on day 22 to 26 (test-of-cure visit), versus 92.1% with azithromycin (n = 38), and the number of treatment failures in each group was 5 and 3, respectively. The difference in cure rate was -7.3%, with a lower limit of the 95% confidence interval (95% CI) of -22.5, and thus, noninferiority was not established at the prespecified margin (lower limit of CI of -15%). The overall treatment-emergent adverse event (TEAE) and treatment-related TEAE rates were lower in the rifalazil group (68% and 55%) than in the azithromycin group (71% and 62%), respectively. Subjects classified as treatment failures at day 22 to 26 had a lower mean plasma concentration of rifalazil at the visit on day 8 to 12 than those classified as treatment cures, but this difference was not significant; however, the levels were similar for both groups at the visit on day 22 to 26. A single 25-mg dose of rifalazil was well tolerated and eradicated C. trachomatis in most of these women with uncomplicated genital C. trachomatis infection. (The study was registered at clinicaltrials.gov under registration no. NCT01631201).

Cumulative clinical experience from over a decade of use of levofloxacin in community-acquired pneumonia: critical appraisal and role in therapy

Levofloxacin is the synthetic L-isomer of the racemic fluoroquinolone, ofloxacin. It interferes with critical processes in the bacterial cell such as DNA replication, transcription, repair, and recombination by inhibiting bacterial topoisomerases. Levofloxacin has broad spectrum activity against several causative bacterial pathogens of community-acquired pneumonia (CAP). Oral levofloxacin is rapidly absorbed and is bioequivalent to the intravenous formulation such that patients can be conveniently transitioned between these formulations when moving from the inpatient to the outpatient setting. Furthermore, levofloxacin demonstrates excellent safety, and has good tissue penetration maintaining adequate concentrations at the site of infection. The efficacy and tolerability of levofloxacin 500 mg once daily for 10 days in patients with CAP are well established. Furthermore, a high-dose (750 mg) and short-course (5 days) of once-daily levofloxacin has been approved for use in the US in the treatment of CAP, acute bacterial sinusitis, acute pyelonephritis, and complicated urinary tract infections. The high-dose, short-course levofloxacin regimen maximizes its concentration-dependent antibacterial activity, decreases the potential for drug resistance, and has better patient compliance.

Antibiotic resistance in Chlamydiae

There are few documented reports of antibiotic resistance in Chlamydia and no examples of natural and stable antibiotic resistance in strains collected from humans. While there are several reports of clinical isolates exhibiting resistance to antibiotics, these strains either lost their resistance phenotype in vitro, or lost viability altogether. Differences in procedures for chlamydial culture in the laboratory, low recovery rates of clinical isolates and the unknown significance of heterotypic resistance observed in culture may interfere with the recognition and interpretation of antibiotic resistance. Although antibiotic resistance has not emerged in chlamydiae pathogenic to humans, several lines of evidence suggest they are capable of expressing significant resistant phenotypes. The adept ability of chlamydiae to evolve to antibiotic resistance in vitro is demonstrated by contemporary examples of mutagenesis, recombination and genetic transformation. The isolation of tetracycline-resistant Chlamydia suis strains from pigs also emphasizes their adaptive ability to acquire antibiotic resistance genes when exposed to significant selective pressure.

Levofloxacin in the treatment of community-acquired pneumonia

Levofloxacin is a fluoroquinolone that has a broad spectrum of activity against several causative bacterial pathogens of community-acquired pneumonia (CAP). The efficacy and tolerability of levofloxacin 500 mg once daily for 10 days in patients with CAP are well established. Furthermore, a high-dose (750 mg), short-course (5 days) of once-daily levofloxacin has been approved for use in the USA in the treatment of CAP, acute bacterial sinusitis, acute pyelonephritis and complicated urinary tract infections. Levofloxacin can be used as a monotherapy in patients with CAP, however, levofloxacin combination therapy with anti-pseudomonal beta-lactam (or aminoglycoside) should be considered if Pseudomonas aeruginosa is the causative pathogen of the respiratory infection. The high-dose, short-course levofloxacin regimen maximizes its concentration-dependent antibacterial activity, decreases the potential for drug resistance and has better patient compliance. Oral levofloxacin is rapidly absorbed and is bioequivalent to the intravenous formulation and the patients can switch between these formulations, which results in more options with respect to the therapeutic regimens. Furthermore, levofloxacin is generally well tolerated, has good tissue penetration and adequate concentrations can be maintained at the site of infections.

Newer antibacterial drugs for a new century

IMPORTANCE OF THE FIELD

Antibacterial drug discovery and development has slowed considerably in recent years, with novel classes discovered decades ago and regulatory approvals tougher to get. Traditional approaches and the newer genomic mining approaches have not yielded novel classes of antibacterial compounds. Instead, improved analogues of existing classes of antibacterial drugs have been developed by improving potency, minimizing resistance and alleviating toxicity.

AREAS COVERED IN THIS REVIEW

This article is a comprehensive review of newer classes of antibacterial drugs introduced or approved after year 2000.

WHAT THE READER WILL GAIN

It describes their mechanisms of action/resistance, improved analogues, spectrum of activity and clinical trials. It also discusses new compounds in development with novel mechanisms of action, as well as novel unexploited bacterial targets and strategies that may pave the way for combating drug resistance and emerging pathogens in the twenty-first century.

TAKE HOME MESSAGE

The outlook of antibacterial drug discovery, though challenging, may not be insurmountable in the years ahead, with legislation on incentives and funding introduced for developing an antimicrobial discovery program and efforts to conserve antibacterial drug use.

New antimicrobial agents for use in the intensive care unit

Timely provision of adequate antimicrobial coverage in an initial anti-infective treatment regimen results in optimal outcomes for bacterial and fungal infections. However, selection of appropriate antimicrobial regimens for treatment of infections in the intensive care unit (ICU) can be challenging due to expansion of resistance, which typically requires use of multidrug anti-infective regimens to provide adequate coverage of important pathogens commonly seen in the ICU setting. Indeed, a recent additional call to action by the Infectious Diseases Society of America (IDSA) has enforced the impact that antimicrobial-resistant pathogens can have on patient care. The term ESKAPE has been coined by this IDSA group to refer to Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumanii, Pseudomonas aeruginosa, and Enterobacter species, the etiologic causes of the majority of hospital-acquired infections in the United States that are able to effectively "escape" our antibiotic arsenal and that also mandate discovery of new antimicrobial agents. This article reviews select antibacterial agents and an antifungal agent in late stages of clinical development that appear to have potential for treatment of infections in the ICU.

Iclaprim: a novel dihydrofolate reductase inhibitor for skin and soft tissue infections

Antibiotic resistance is an ever-increasing concern in the treatment of severe skin and skin-structure infections, pneumonia, bacteremia and other serious infections caused by methicillin-resistant Staphylococcus aureus, vancomycin-resistant S. aureus, group A Streptococcus and vancomycin-resistant Enterococcus. In this review, we summarize the current status of both US FDA-approved and investigational agents aimed at this group of pathogens. We also describe, in detail, the chemistry, mechanism of action, pharmacokinetic properties and spectrum of microbiological activity of iclaprim, a novel dihydrofolate reductase inhibitor recently awarded fast-track approval status by the FDA. Finally, we review the clinical efficacy of iclaprim compared with linezolid for skin and skin-structure infections as demonstrated in Phase III randomized, controlled trials, and comment on its potential role in the treatment of other severe infections with drug-resistant Gram-positive pathogens.

In vitro activity of Iclaprim against respiratory and bacteremic isolates of Streptococcus pneumoniae

Iclaprim, a novel dihydrofolate reductase inhibitor, inhibited 90% of the clinical isolates (MIC(90)) of Streptococcus pneumoniae (n = 785) collected by a national surveillance program at a concentration of 1 microg/ml. The MIC(90) for iclaprim was 7 doubling dilutions lower for trimethoprim-sulfamethoxazole-susceptible isolates (n = 670; MIC(90), 0.06 microg/ml) than for trimethoprim-sulfamethoxazole-resistant isolates (n = 115; MIC(90), >or=8 microg/ml). The potential clinical utility of iclaprim to treat patients with pneumococcal infections may depend upon the current prevalence of resistance to trimethoprim-sulfamethoxazole in this pathogen.

Levofloxacin : a review of its use as a high-dose, short-course treatment for bacterial infection

Levofloxacin (Levaquin) is a fluoroquinolone antibacterial that is the L-isomer of ofloxacin. A high-dose (750 mg) short-course (5 days) of once-daily levofloxacin is approved for use in the US in the treatment of community-acquired pneumonia (CAP), acute bacterial sinusitis (ABS), complicated urinary tract infections (UTI) and acute pyelonephritis (AP). The broad spectrum antibacterial profile of levofloxacin means that monotherapy is often a possibility in patients with CAP at times when other agents may require combination therapy, although levofloxacin can be used in combination therapy when necessary. The high-dose, short-course levofloxacin regimen maximizes its concentration-dependent bactericidal activity and may reduce the potential for resistance to emerge. In addition, this regimen lends itself to better compliance because of the shorter duration of treatment and the convenient once-daily administration schedule. Oral levofloxacin is rapidly absorbed and is bioequivalent to the intravenous formulation; importantly, patients can transition between the formulations, which results in more options in regards to the treatment regimen and the potential for patients with varying degrees of illness to be treated. Levofloxacin has good tissue penetration and an adequate concentration can be maintained in the urinary tract to treat uropathogens. Levofloxacin is generally well tolerated and has good efficacy in the treatment of patients with CAP, ABS, complicated UTI and AP. The efficacy and tolerability of levofloxacin 500 mg once daily for 10 days in patients with CAP, ABS and UTIs is well established, and the high-dose, short-course levofloxacin regimen has been shown to be noninferior to the 10-day regimen in CAP and ABS, and to have a similar tolerability profile. Similarly, the high-dose, short-course levofloxacin regimen is noninferior to ciprofloxacin in patients with complicated UTI or AP. Thus, levofloxacin is a valuable antimicrobial agent that has activity against a wide range of bacterial pathogens; however, its use should be considered carefully so that the potential for resistance selection can be minimized and its usefulness in severe infections and against a range of penicillin- and macrolide-resistant pathogens can be maintained.

Pharmacologic options for CNS infections caused by resistant Gram-positive organisms

Infectious disease continues to evolve, presenting new and challenging clinical situations for practitioners. Specific to device-related and neurosurgical-related CNS infections, Gram-positive organisms are of growing concern. Current Infection Disease Society of America guidelines for the treatment of CNS infections offer little direction after conventional therapy, consisting of vancomycin, has failed or the patient has demonstrated intolerance. A review of literature evaluating alternative therapies, specifically linezolid, quinupristin/dalfopristin, daptomycin and tigecycline, will be presented. Interpretations of these data are offered followed by a brief presentation of future therapies, including ortavancin, telavancin, dalbavancin, ceftobiprole and iclaprim, all of which possess potent Gram-positive activity.

Azithromycin extended release: a review of its use in the treatment of acute bacterial sinusitis and community-acquired pneumonia in the US

Azithromycin is a macrolide antibacterial agent. The novel microspheres oral extended-release formulation (Zmax) is the first antibacterial drug approved in the US for administration as a single dose in adult patients with mild to moderate acute bacterial sinusitis (ABS) or community-acquired pneumonia (CAP). It has a broad spectrum of in vitro antibacterial activity against Gram-positive, Gram-negative and atypical pathogens that cause ABS and CAP infections (including Streptococcus pneumoniae), and achieves good tissue penetration. Azithromycin extended release is an effective and generally well tolerated treatment in patients with ABS or CAP. The clinical cure rates of a single 2.0 g dose of azithromycin extended release were noninferior to those obtained with a 10-day regimen of levofloxacin in patients with ABS, and with 7-day regimens of clarithromycin extended release or levofloxacin in patients with CAP. With a pharmacodynamic and pharmacokinetic profile well suited to administration as a single-dose regimen that may offer the advantage of improved compliance and convenience compared with once-daily longer-course regimens, azithromycin extended release is a new option in the empirical treatment of adult patients with mild or moderate ABS or CAP in the US.

Investigational treatments for postoperative surgical site infections

Surgical site infections rank third among nosocomial infections, representing a global threat, associated with the emergence of multi-drug-resistant bacteria. The pharmaceutical industry has recently curtailed developmental programmes; however, the need for new compounds is extremely important. This article reviews new antimicrobials and immunointerventional targets for their potential to treat surgical site infections in comparison with recently licensed compounds. Daptomycin, dalbavancin, oritavancin, telavancin, iclaprim and ranbezolid seem to be promising agents against infections caused by Gram-positive pathogens and effectively address the present problems of multi-resistance in Gram-positive infections. Peptide deformylase inhibitors and immunostimulating agents open new perspectives in this field; however, very few compounds targeting Gram-negative problematic pathogens are in the pipeline of the future. Tigecycline (recently marketed) ceftobiprole, ceftaroline and doripenem seem to possess an extended anti-Gram-positive and -negative spectrum. Among these compounds, only doripenem demonstrates activity against Pseudomonas aeruginosa, for which there is a clear unmet need for new compounds, focusing on new targets.

Dihydrofolate reductase inhibitors as antibacterial agents

Although only a few DHFR inhibitors have progressed as antibiotics to the market there is much renewed interest in the discovery and development of new generation DHFR inhibitors as antibacterial agents. This article describes the success in exploiting DHFR as a drugable target as exemplified by trimethoprim (TMP) and the development of several new diaminopyrimidines. Iclaprim, a recent example of a novel diaminopyrimidine currently in Phase III clinical trials, is also described together with several examples of anti-DHFR antibacterial compounds in pre-clinical development.

New advances in antibiotic development and discovery

The development of new antibiotics is crucial to controlling current and future infectious diseases caused by antibiotic-resistant bacteria. Increased development costs, the difficulty in identifying new drug classes, unanticipated drug toxicities, the ease by which bacteria develop resistance to new antibiotics and the failure of many agents to address antibiotic resistance specifically, however, have all led to an overall decline in the number of antibiotics that are being introduced into clinical practice. Although there are few, if any, advances likely in the immediate future, there are agents in both clinical and preclinical development that can address some of the concerns of the infectious disease community. Many of these antibiotics will be tailored to specific infections caused by a relatively modest number of susceptible and resistant organisms.