Streptococcus pneumoniae resistance to fluoroquinolones

New Developments in Antibacterial Choice for Lower Respiratory Tract Infections in Elderly Patients

Elderly patients are at increased risk of developing lower respiratory tract infections compared with younger patients. In this population, pneumonia is a serious illness with high rates of hospitalisation and mortality, especially in patients requiring admission to intensive care units (ICUs). A wide range of pathogens may be involved depending on different settings of acquisition and patient's health status. Streptococcus pneumoniae is the most common bacterial isolate in community-acquired pneumonia, followed by Haemophilus influenzae, Moraxella catarrhalis and atypical pathogens such as Chlamydia pneumoniae, Legionella pneumophila and Mycoplasma pneumoniae. However, elderly patients with comorbid illness, who have been recently hospitalised or are residing in a nursing home, may develop severe pneumonia caused by multidrug resistant staphylococci or pneumococci, and enteric Gram-negative bacilli, including Pseudomonas aeruginosa. Moreover, anaerobes may be involved in aspiration pneumonia. Timely and appropriate empiric treatment is required in order to enhance the likelihood of a good clinical outcome, prevent the spread of antibacterial resistance and reduce the economic impact of pneumonia. International guidelines recommend that elderly outpatients and inpatients (not in ICU) should be treated for the most common bacterial pathogens and the possibility of atypical pathogens. The algorithm for therapy is to use either a selected beta-lactam combined with a macrolide (azithromycin or clarithromycin), or to use monotherapy with a new anti-pneumococcal quinolone, such as levofloxacin, gatifloxacin or moxifloxacin. Oral (amoxicillin, amoxicillin/clavulanic acid, cefuroxime axetil) and intravenous (sulbactam/ampicillin, ceftriaxone, cefotaxime) beta-lactams are agents of choice in outpatients and inpatients, respectively. For patients with severe pneumonia or aspiration pneumonia, the specific algorithm is to use either a macrolide or a quinolone in combination with other agents; the nature and the number of which depends on the presence of risk factors for specific pathogens. Despite these recommendations, clinical resolution of pneumonia in the elderly is often delayed with respect to younger patients, suggesting that optimisation of antibacterial therapy is needed. Recently, some new classes of antibacterials, such as ketolides, oxazolidinones and streptogramins, have been developed for the treatment of multidrug resistant Gram-positive infections. However, the efficacy and safety of these agents in the elderly is yet to be clarified. Treatment guidelines should be modified on the basis of local bacteriology and resistance patterns, while dosage and/or administration route of each antibacterial should be optimised on the basis of new insights on pharmacokinetic/pharmacodynamic parameters and drug interactions. These strategies should be able to reduce the occurrence of risk factors for a poor clinical outcome, hospitalisation and death.

Fluoroquinolone AUIC break points and the link to bacterial killing rates. Part 1: In vitro and animal models

OBJECTIVE

To review in vitro and animal model studies with fluoroquinolones and the pharmacokinetic and pharmacodynamic relationships that are predictive of clinical and microbiologic outcomes and resistance. Data on fluoroquinolones are summarized and examine the premise that a single area under the inhibitory concentration-time curve (AUIC) target >125 may be used for all fluoroquinolones with concentration-dependent killing actions and against all target organisms.

DATA SOURCES

Primary articles were identified by MEDLINE search (1966-February 2002) and through secondary sources.

STUDY SELECTION AND DATA EXTRACTION

All of the articles identified from the data sources were evaluated, and all information deemed relevant was included.

DATA SYNTHESIS

The fluoroquinolones exhibit concentration-dependent killing. This effect clearly depends on concentrations achieved, and outcomes depend on endpoints established by individual investigators. With AUIC values <60, the actions of fluoroquinolones are essentially bacteriostatic; any observed bacterial killing is the combined effect of low concentrations in relation to minimum inhibitory concentration and the action of host factors such as neutrophils and macrophages. AUIC values >100 but <250 yield bacterial killing at a slow rate, but usually by day 7 of treatment. AUICs >250 produce rapid killing, and bacterial eradication occurs within 24 hours. Disagreements regarding target endpoints are the expected consequences of comparing microbial and clinical outcomes across animal models, in vitro experiments, and humans when the endpoints are clearly not equivalent. Careful attention to time-related events, such as speed of bacterial killing, versus global endpoints, such as bacteriologic cure, allows optimal break points to be defined.

CONCLUSIONS

Evidence from in vitro and animal models favors the use of AUIC values >250 for rapid bactericidal action, regardless of whether the organism is gram-negative or gram-positive.

Fluoroquinolones, tuberculosis, and resistance

Although the fluoroquinolones are presently used to treat tuberculosis primarily in cases involving resistance or intolerance to first-line antituberculosis therapy, these drugs are potential first-line agents and are under study for this indication. However, there is concern about the development of fluoroquinolone resistance in Mycobacterium tuberculosis, particularly when administered as monotherapy or as the only active agent in a failing multidrug regimen. Treatment failures as well as relapses have been documented under such conditions. With increasing numbers of fluoroquinolone prescriptions and the expanded use of these broad-spectrum agents for many infections, the selective pressure of fluoroquinolone use results in the ready emergence of fluoroquinolone resistance in a diversity of organisms, including M tuberculosis. Among M tuberculosis, resistance is emerging and may herald a significant future threat to the long-term clinical utility of fluoroquinolones. Discussion and education regarding appropriate use are necessary to preserve the effectiveness of this antibiotic class against the hazard of growing resistance.

The battle against emerging antibiotic resistance: should fluoroquinolones be used to treat children?

Inappropriate use of antibiotic drugs in humans and animals has led to widespread resistance among microbial pathogens. Resistance is the phenotypic expression corresponding to genetic changes caused by either mutation or acquisition of new genetic information. In some cases, multidrug resistance occurs. Streptococcus pneumoniae is one of the most important respiratory pathogens, playing a major role in both upper and lower respiratory tract infections. Pneumococcal resistance to antimicrobials may be acquired by means of horizontal transfer followed by homologous recombination of genetic material from the normal flora of the human oral cavity or by means of mutation. Resistance to penicillins and macrolides has been increasing for some time, but, recently, fluoroquinolone resistance has become an issue as well. We are concerned that, if fluoroquinolones are approved for use in children, their widespread use will result in rapid emergence of pneumococcal resistance, because children are more often colonized in the nasopharynx with high-density populations of pneumococci than are adults.

Streptococcus pneumoniae response to repeated moxifloxacin or levofloxacin exposure in a rabbit tissue cage model

The role of moxifloxacin and levofloxacin pharmacokinetics (PK) in antimicrobial efficacy and in the selection of fluoroquinolone-resistant Streptococcus pneumoniae strains was investigated using the rabbit tissue cage abscess model. A rabbit tissue cage was created by insertion of sterile Wiffle balls in the dorsal cervical area. Animals orally received a range of moxifloxacin or levofloxacin doses that simulate human PK for 7 days 48 h after the Wiffle balls were inoculated with fluoroquinolone-sensitive S. pneumoniae (10(7) CFU). Abscess fluid was collected on a daily basis over 14 days to measure bacterial density and MICs. Moxifloxacin regimens produced a range of area under the concentration-time curve (AUC)/MIC ratios ranging from 9.2 to 444 and peak/MIC ratios ranging from 1.3 to 102. Levofloxacin doses produced AUC/MIC ratios of 5.1 to 85.5 and peak/MIC ratio of 0.9 to 14.8. Moxifloxacin at 6.5, 26, and 42 mg/kg reduced the bacterial log CFU per milliliter in abscess fluid (percentage of that in a sterile animal) by 4.2 +/- 2.2 (20%), 5.8 +/- 0.4 (100%), and 5.4 +/- 0.4 (100%), respectively, over the dosing period. Levofloxacin at 5.5, 22, and 32 mg/kg reduced the log CFU per milliliter in abscess fluid (percentage of that in a sterile animal) by 2.8 +/- 0.7 (20%), 5.1 +/- 1.3 (80%), and 4.6 +/- 1.3 (60%), respectively. Moxifloxacin has a greater bactericidal rate as determined by regression of log CFU versus time data. The AUC/MIC and peak/MIC ratios correlated with the efficacy of both drugs (P < 0.05). Resistance to either drug did not develop with any of the doses as assessed by a change in the MIC. In conclusion, data derived from this study show that moxifloxacin and levofloxacin exhibit rapid bactericidal activity against S. pneumoniae in vivo, and moxifloxacin exhibits enhanced bactericidal activity compared to levofloxacin, with AUC/MIC and peak/MIC ratios correlated with antimicrobial efficacy for both drugs. The development of fluoroquinolone-resistant S. pneumoniae was not observed with either drug in this model.

Gemifloxacin: survival of the fittest

The incidence of penicillin resistance in pneumococci is increasing in the USA, having risen from <5% before 1989 to >35% in 1997. There has also been a shift in the ratio of intermediate to high-level resistance from 3 or 4:1 to 2 or 1:1. Multidrug resistance and resistance to macrolides and fluoroquinolones in pneumococci is also a matter of concern. The implications for empirical treatment of respiratory tract infections are considerable. The potential of quinolones with activity against respiratory pathogens including pneumococci must be preserved by careful antimicrobial prescribing.

The drug-resistant pneumococcus: clinical relevance, therapy, and prevention

Streptococcus pneumoniae has been known for > 100 years as the most important bacterial pathogen of the respiratory tract in adults and children. In recent years, the pneumococcus has begun to exhibit increasing resistance to antimicrobial agents. Because of the huge number of infections caused by this organism, the development of resistance has changed the approach to many infectious disease problems, particularly with regard to empiric antibiotic therapy and prophylaxis. In our review of the antibiotic-resistant pneumococcus, we review the microbiologic basis for resistance, risk factors for and clinical relevance of infection by a resistant organism, and infection control measures.

Drug-resistant pathogens in community- and hospital-acquired pneumonia

Antimicrobial resistance has been a problem since the early days of the antibiotic era, but in recent years, this resistance has increased in the hospital and is being recognized more in the community setting. Respiratory pathogens such as S. pneumoniae and H. influenzae, for example, have developed resistance to traditional antimicrobial therapy, often over a very short period of time. This increase in resistance patterns requires physicians to closely monitor antimicrobial resistance in their community and to appreciate that some antimicrobial resistance mechanisms may result in resistance for a complete class of antibiotics or different classes of antibiotics with similar mechanisms of action.

Antibiotic therapy for community-acquired pneumonia

This article takes a broad perspective of community-acquired pneumonia (CAP). The arguments and data that support or refute the current approaches to initial antimicrobial treatment of CAP as outlined in the American Thoracic Society and Infectious Disease Society of America documents are provided. The complex issues involved in the decision of how to properly treat CAP are addressed.

Decreased susceptibility of Streptococcus pneumoniae to fluoroquinolones in Canada. Canadian Bacterial Surveillance Network

BACKGROUND

Fluoroquinolones are now recommended for the treatment of respiratory tract infections due to Streptococcus pneumoniae, particularly when the isolates are resistant to beta-lactam antibiotics. Although pneumococci with reduced susceptibility to fluoroquinolones have been identified, their prevalence has not been determined in a defined population.

METHODS

We performed susceptibility testing on 7551 isolates of S. pneumoniae obtained from surveillance in Canada in 1988 and from 1993 to 1998. Pneumococci with reduced susceptibility to fluoroquinolones (defined as a minimal inhibitory concentration of ciprofloxacin of at least 4 microg per milliliter) were further characterized. We also examined antibiotic prescriptions dispensed in Canadian retail pharmacies.

RESULTS

Between 1988 and 1997, fluoroquinolone prescriptions increased from 0.8 to 5.5 per 100 persons per year. The prevalence of pneumococci with reduced susceptibility to fluoroquinolones increased from 0 percent in 1993 to 1.7 percent in 1997 and 1998 (P=0.01). Among adults, the prevalence increased from 1.5 percent in 1993 and 1994 combined to 2.9 percent in 1997 and 1998 combined. The prevalence was higher in isolates from older patients (2.6 percent among those 65 years of age or older vs. 1.0 percent among those 15 to 64 years of age, P<0.001) and among those from Ontario (1.5 percent, vs. 0.4 percent among those from the rest of Canada; P< 0.001). Fluoroquinolone use was greatest among the elderly and in Ontario. The 75 isolates (17 serotypes) of pneumococci with reduced susceptibility to fluoroquinolones were submitted by 40 laboratories in eight provinces. Reduced susceptibility to fluoroquinolones was associated with resistance to penicillin.

CONCLUSIONS

The prevalence of pneumococci with reduced susceptibility to fluoroquinolones is increasing in Canada, probably as a result of selective pressure from the increased use of fluoroquinolones.

The new fluoroquinolones: A critical review

OBJECTIVE

This paper reviews the literature available on the new fluoroquinolones - clinafloxacin, gatifloxacin, grepafloxacin, levofloxacin, moxifloxacin, sparfloxacin and trovafloxacin - to compare these agents with each other and contrast them with ciprofloxacin, an older fluoroquinolone.

DATA SELECTION

Published papers used were obtained by searching MEDLINE for articles published between 1994 and 1998, inclusive. References of published papers were also obtained and reviewed. Abstracts from scientific proceedings were reviewed.

DATA EXTRACTION

Due to the limited data available on several of the agents, criteria for study inclusion in the in vitro, pharmacokinetics and in vivo sections were not restrictive.

DATA SYNTHESIS

The new fluoroquinolones offer excellent Gram-negative bacillary activity and improved Gram-positive activity (eg, against Streptococcus pneumoniae and Staphylococcus aureus) over ciprofloxacin. Clinafloxacin, gatifloxacin, moxifloxacin, sparfloxacin and trovafloxacin display improved activity against anaerobes (eg, Bacteriodes fragilis). All of the new fluoroquinolones have a longer serum half-life than ciprofloxacin (allowing for once daily dosing), and several are eliminated predominantly by nonrenal means. No clinical trials are available comparing the new fluoroquinolones with each other. Clinical trials comparing the new fluoroquinolones with standard therapy have demonstrated good efficacy in a variety of infections. Their adverse effect profile is similar to that of ciprofloxacin. Clinafloxacin and sparfloxacin cause a high incidence of phototoxicity (1.5% to 14% and 2% to 11.7%, respectively), grepafloxacin causes a high incidence of taste perversion (9% to 17%) and trovafloxacin causes a high incidence of dizziness (11%). They all interact with metal ion-containing drugs (eg, antacids), and clinafloxacin and grepafloxacin interact with theophylline. The new fluoroquinolones are expensive; however, their use may result in savings in situations where, because of their potent and broad spectrum of activity, they can be used orally in place of intravenous antibiotics.

CONCLUSIONS

The new fluoroquinolones offer advantages over ciprofloxacin in terms of improved in vitro activity and pharmacokinetics. Whether these advantages translate into improved clinical outcomes is presently unknown. The new fluoroquinolones have the potential to emerge as important therapeutic agents in the treatment of respiratory tract and genitourinary tract infections.

Advances in antimicrobial therapy of community-acquired pneumonia

Community-acquired pneumonia has a significant impact upon healthcare in North America and worldwide. In the U.S. it is responsible for three to four million cases yearly and 78,000 deaths. It is not a homogeneous entity and it may be caused by a number of pathogens including Streptococcus pneumoniae, the atypicals (Mycoplasma pneumoniae, Chlamydia pneumoniae and Legionella species) Haemophilus influenzae and Gram-negative rods. While it is clear that directed therapy is the ideal, empiric therapy is likely to remain the norm for some time to come. This is because of limitations in current diagnostic techniques, the possibility of infection with co-pathogens and the broad spectrum of antimicrobial activity required to treat the various pathogens which may be responsible for infection in any given patient. Of great concern is the increase in the incidence of resistant pathogens seen in community-acquired pneumonia. Of particular significance are the isolates of S. pneumoniae which display resistance to penicillin and macrolides although the exact clinical relevance has yet to be determined. New guidelines for the treatment of community-acquired pneumonia have been developed by the Infectious Disease Society of America which include the new fluoroquinolones. These agents offer the potential for monotherapy of community-acquired pneumonia in cases which previously required combination regimens such as a macrolide and a beta-lactam. There is great concern however, that these agents not be used inappropriately thereby hastening the emergence of resistance to the fluoroquinolone class of antimicrobials.

Resistance issues and treatment implications: pneumococcus, Staphylococcus aureus, and gram-negative rods

During the last decade there has been an unexpectedly rapid evolution of antimicrobial resistance in the respiratory pathogens for community- and hospital-acquired pneumonia. In order to choose the most optimal therapy for their patients, it is essential that physicians be aware of the prevalence and mechanisms of resistance and their implications on the effectiveness of the various antimicrobials.

A comparison of the activity of ciprofloxacin and levofloxacin with other agents against respiratory tract pathogens

In a study involving 15 UK hospitals, sequential respiratory tract isolates of Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis were studied. The susceptibility of these strains to two fluoroquinolones, ciprofloxacin and levofloxacin were compared to those of currently used macrolides and beta-lactams. The activity of ciprofloxacin and levofloxacin against S. pneumoniae was not statistically significantly different (geometric mean MIC 0.978 and 0.95 mg/L respectively). Beta-lactam resistance did not affect fluoroquinolone susceptibility. H. influenzae and M. catarrhalis were highly susceptible to both fluoroquinolones.