Levofloxacin failure in a patient with pneumococcal pneumonia

Ceftaroline versus ceftriaxone in a highly penicillin-resistant pneumococcal pneumonia rabbit model using simulated human dosing

Ceftaroline (CPT) is a new cephalosporin exhibiting bactericidal activity against Gram-positive organisms, including methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant Streptococcus pneumoniae (MDRSP), as well as common Gram-negative pathogens. This study investigated the in vivo efficacy of a 48-hour simulated human dose regimen of CPT compared with ceftriaxone (CRO) against isolates of S. pneumoniae with different susceptibilities to penicillin in a rabbit pneumonia model. Three S. pneumoniae strains were used: CRO-susceptible penicillin-susceptible S. pneumoniae (CRO-S PSSP), CRO-susceptible penicillin-intermediate S. pneumoniae (CRO-S PISP), and CRO-resistant penicillin-resistant S. pneumoniae (CRO-R PRSP). Animals were randomized to the control group (no treatment) (n = 22) or to a group given intravenous (IV) CPT human equivalent (HE) dosage (600 mg/12 h; n = 19) or IV CRO HE dosage (1 g/24 h; n = 19). The total doses needed to achieve the HE dosage were 71 and 82 mg/kg of body weight/24 h for CRO and CPT, respectively. One group of rabbits infected with the CRO-R PRSP strain received intramuscular (IM) administration of CPT (5 or 20 mg/kg twice daily; n = 5 for each). Evaluation of efficacy was based on bacterial counts in the lungs and spleen. For IV CPT and IV CRO, the mean areas under the concentration-time curves from 0 to 24 h (AUC(0-24)s) were 155 and 938 mg · h/liter, respectively, the maximum concentrations in serum (C(max)s) were 20 and 158 mg/liter, respectively, and the minimum concentrations in serum (C(min)s) were 1.3 and 6 mg/liter, respectively. Both agents effectively treated pulmonary infections caused by CRO-S PSSP or CRO-S PISP with complete bacterial eradication in the lungs and spleen after 2 days of treatment. Against PRSP, CPT demonstrated excellent bactericidal activity, reducing bacterial counts in the lungs and spleen by approximately 8 and 4 log units, respectively (P < 0.001); CRO treatment resulted in a 2-log-unit reduction in the bacterial counts in lungs that did not reach statistical significance. Twice-daily IM CPT (5 mg/kg) reduced the bacterial burden by approximately 6 log units in the lungs and 3 log units in the spleen, and the 20-mg/kg dosage effectively eradicated PRSP infection. These findings further validate the in vivo bactericidal activity of CPT against pneumococci.

Prophylactic antibiotics in aesthetic surgery

Improvements in infection prevention practices over the past several decades have enhanced outcomes following aesthetic surgery. However, surgical site infections (SSI) continue to result in increased morbidity, mortality, and cost of care. The true incidence rate of SSI in aesthetic surgery is unknown due to the lack of a national surveillance system, but studies of SSI across surgical specialties have suggested that many of these infections are preventable. Patient-related factors-including obesity, glycemic control, and tobacco use-may contribute to the development of SSI following aesthetic surgery. In terms of SSI prevention, proper handwashing and surgical skin preparation are integral. Furthermore, the administration of prophylactic antibiotics has been shown to reduce SSI following many types of surgical procedures. Unfortunately, there are few large, randomized studies examining the role of prophylactic antibiotics in aesthetic surgery. The authors review the medical literature, discuss the risks of antibiotic overutilization, and detail nonpharmacological methods for reducing the risk of SSI.

An antimicrobial stewardship program with a focus on reducing fluoroquinolone overuse

The fluoroquinolones have become the leading class of antimicrobial agents prescribed to adults in the United States. Resistance of key pathogens to fluoroquinolones has developed rapidly in parallel with increased prescribing of these drugs. We describe our pharmacist-led antimicrobial stewardship program that focused on reducing inappropriate prescribing of fluoroquinolones, with the goals of limiting the development of resistance and improving patient outcomes. Core strategies were regular monitoring and reporting of resistance trends observed on institutional antibiograms, performing drug audits and related studies with intervention and feedback to prescribers, implementing an automatic parenteral-to-oral conversion program, establishing and implementing a beta-lactam-based institutional guideline for empiric therapy, and educating prescribers. This successful program reduced empiric prescribing of fluoroquinolones by 30%, improved susceptibility for all antipseudomonal agents against Pseudomonas aeruginosa overall by 10%, and decreased mortality associated with P. aeruginosa infections by 2-fold. Our stewardship program clearly demonstrated that pharmacists can take on leadership roles to positively change antimicrobial prescribing at the institutional level and improve patient outcomes.

The etiology of community-acquired pneumonia in Australia: why penicillin plus doxycycline or a macrolide is the most appropriate therapy

BACKGROUND

Available data on the etiology of community-acquired pneumonia (CAP) in Australia are very limited. Local treatment guidelines promote the use of combination therapy with agents such as penicillin or amoxycillin combined with either doxycycline or a macrolide.

METHODS

The Australian CAP Study (ACAPS) was a prospective, multicenter study of 885 episodes of CAP in which all patients underwent detailed assessment for bacterial and viral pathogens (cultures, urinary antigen testing, serological methods, and polymerase chain reaction). Antibiotic agents and relevant clinical outcomes were recorded.

RESULTS

The etiology was identified in 404 (45.6%) of 885 episodes, with the most frequent causes being Streptococcus pneumoniae (14%), Mycoplasma pneumoniae (9%), and respiratory viruses (15%; influenza, picornavirus, respiratory syncytial virus, parainfluenza virus, and adenovirus). Antibiotic-resistant pathogens were rare: only 5.4% of patients had an infection for which therapy with penicillin plus doxycycline would potentially fail. Concordance with local antibiotic recommendations was high (82.4%), with the most commonly prescribed regimens being a penicillin plus either doxycycline or a macrolide (55.8%) or ceftriaxone plus either doxycycline or a macrolide (36.8%). The 30-day mortality rate was 5.6% (50 of 885 episodes), and mechanical ventilation or vasopressor support were required in 94 episodes (10.6%). Outcomes were not compromised by receipt of narrower-spectrum beta-lactams, and they did not differ on the basis of whether a pathogen was identified.

CONCLUSIONS

The vast majority of patients with CAP can be treated successfully with narrow-spectrum beta-lactam treatment, such as penicillin combined with doxycycline or a macrolide. Greater use of such therapy could potentially reduce the emergence of antibiotic resistance among common bacterial pathogens.

Oral garenoxacin in the treatment of acute bacterial maxillary sinusitis: a Phase II, multicenter, noncomparative, open-label study in adult patients undergoing sinus aspiration

BACKGROUND

Garenoxacin is a des-F(6)-quinolone with in vitro activity against key respiratory pathogens, including Streptococcus pneumoniae, Hemophilus influenzae, Staphylococcus aureus, and Moraxella catarrhalis. Limited data are available regarding the effect of garenoxacin in the treatment of acute bacterial sinusitis.

OBJECTIVE

The aim of this study was to assess the efficacy and tolerability of garenoxacin in adults with acute bacterial maxillary sinusitis undergoing a pre-treatment diagnostic sinus aspirate.

METHODS

This Phase II, multicenter, noncomparative, open-label study was conducted at 30 centers in the United States, Mexico, Argentina, and Europe. Male and female patients aged 18 to 80 years with clinical signs and symptoms lasting >or=5 but <or=28 days and radiologic signs (air-fluid level, opacification, mucosal thickening) of acute maxillary sinusitis were eligible. The entry criteria for the 5-day treatment regimen did not include mucosal thickening of >or=5 mm because it was believed that improvement in mucosal thickening might not be reliably measurable at the 5-day time point. All patients received garenoxacin 400 mg QD for 5 or 10 days. Maxillary sinus needle aspiration for Gram stain, routine culture, and susceptibility testing were performed before treatment, and, if clinically indicated, during and after treatment. Bacteriologic eradication (negative culture on repeat sinus aspiration) and cure rates (complete resolution of all signs and symptoms) were assessed at a test-of-cure visit 5 to 18 days after the end of treatment. The occurrence of adverse events was recorded by the investigators up to 30 days after the last administration of garenoxacin by questioning patients.

RESULTS

A total of 546 patients were enrolled and 543 were randomized (5-day cohort: mean age, 40 years; mean weight, 76 kg; 56% women; 10-day cohort: mean age, 41 years; mean weight, 77 kg; 58% women). Clinically evaluable patients included 253 in the 5-day cohort and 266 in the 10-day cohort. Cure rates were 93% (236/253; 95% CI, 89%-96%) and 91% (243/266; 95% CI, 87%-94%) for evaluable patients in the 5- and 10-day cohorts, respectively. Bacteriologic eradication rates in microbiologically evaluable patients were 94% in both cohorts (5 days, 204/217; 10 days, 182/193). Eradication rates in the 5- and 10-day cohorts were as follows: S pneumoniae, 94% (62/66) and 93% (39/42); H influenzae, 100% (30/30) and 93% (26/28); S aureus, 96% (23/24) and 91% (31/34); and M catarrhalis, 89% (8/9) and 86% (12/14). Of the 9 patients with acute bacterial sinusitis due to multidrug-resistant S pneumoniae, 8 achieved clinical cure with garenoxacin treatment. Adverse events (AEs) most frequently reported were diarrhea (<or=2%), nausea (2%-6%), headache (2%-6%), and dizziness (<or=2%). Two percent of patients withdrew because of an AE (allergic reaction, adverse gastrointestinal effects, dyspnea, dizziness, headache, or elevation in liver enzymes).

CONCLUSION

In this population of patients with signs and symptoms of acute maxillary sinusitis, oral garenoxacin 400 mg QD for 5 or 10 days eradicated 94% of bacterial pathogens associated with acute bacterial sinusitis in this population and appeared to be well tolerated in adults.

[Will we still have antibiotics tomorrow?]

Since the discovery of antibiotics, it has been generally believed that these antimicrobials are capable of curing almost all bacterial infections. More recently, the appearance of increasing resistance to antibiotics and the emergence of multiresistant microorganisms have given rise to growing concern among physicians, and that concern has now started to filter through to society in general. The problem is further aggravated by a situation that not many people are currently aware of, that is, the limited prospects for future development of new antibiotics in the short to medium term. Appropriate use of available antibiotics based on a thorough understanding of their in vivo activity and the emergence of new forms of administration, such as inhalers, may help to alleviate the problem.

Cross-over assessment of serum bactericidal activity of moxifloxacin and levofloxacin versus penicillin-susceptible and penicillin-resistant Streptococcus pneumoniae in healthy volunteers

We compared the serum bactericidal activity (SBA) of moxifloxacin and levofloxacin against penicillin-susceptible and penicillin-resistant Streptococcus pneumoniae in 12 healthy volunteers. Each subject received 3 days of oral moxifloxacin 400 mg daily and levofloxacin 750 mg daily, respectively, with a 2- to 4-week washout period between regimens. Blood was drawn at 6 time points after the third dose of each antibiotic. Mean serum bactericidal titers (MSBTRs) for moxifloxacin were 4-fold higher than the mean titers for levofloxacin at each time point. For each drug, MSBTRs at each time point were the same or within one 2-fold dilution when analyzed according to the penicillin susceptibility of the strains or the sex of the subjects. The difference in SBA of the 2 drugs may have implications for the emergence of resistance and clinical outcome.

[Antibiotherapy for acute CAP in adults]

Community acquired pneumonia is one of the most frequent infections. With time, bacterial epidemiology and bacterial resistance evolve and new antibiotics become available. So an up-date on adequate antibiotic use is necessary. We reviewed the epidemiology of pneumonia and the evolution of bacterial resistance. We also collected data on new antibiotics which can be used for this infection such as levofloxacin, moxifloxacin, telithromycin, and pristinamycin. All these drugs are effective on bacteria involved in pneumonia. At this time, only few Streptococcus pneumoniae strains have developed resistance to these drugs. However, resistance to fluoroquinolones is not easily detected with common laboratory techniques. There is no effectiveness difference between the 2 new fluoroquinolones (levofloxacin, moxifloxacin) in clinical studies. However, in bacteriological and pharmacological studies, moxifloxacin seems to be more effective than levofloxacin (500 mg/day). For the treatment of pneumonia due to Legionella pneumophila, fluoroquinolones are now widely recommended. For Streptococcus pneumonia, amoxicillin remain the drug of choice, even for bacteria with a decreased susceptibility to penicillin. The importance of treating atypical pathogens remains to be documented.

In vitro susceptibility testing versus in vivo effectiveness

The clinical relevance of susceptibility testing has always been questioned because of the difficulty of correlating in vitro susceptibility testing with in vivo clinical effectiveness. Clearly there have always been host/pathogen factors that influence the clinical outcome that cannot be predicted by the results of susceptibility testing. However, improved understanding of pharmacodynamic and pharmacokinetic parameters has greatly improved the use of antimicrobial agents. Most importantly, the integration of these pharmacodynamic and pharmacokinetic indices has greatly improved the correlation between in vitro susceptibility testing and in vivo clinical effectiveness and allows more realistic breakpoints. Finally, the clinical microbiology laboratory has advanced with improved methods as well as the adaptation of breakpoints that are more realistic.

Antibiothérapie des pneumonies aiguës communautaires à Streptococcus pneumoniae : impact clinique de la résistance bactérienne

The emergence of Streptococcus pneumoniae strains with reduced susceptibility to beta-lactams and with multiple drug resistance has not led to major changes in recommendations for antibiotic therapy in patients with acute community-acquired pneumococcal pneumonia. Numerous factors explain the limited clinical impact of this major microbiological change. The frequency of intermediate strains is high but the frequency of resistant strains to beta-lactams is very low. There is a complex relation between the acquisition of resistance to beta-lactams and the decreased virulence of S. pneumoniae strains. The only finding in studies of humanized experimental animal models of lethal bacteremic pneumonia caused by resistance and tolerant strains was a slowing in the kinetics of beta-lactams bactericidal activity, especially for amoxicillin. Taken together, this preclinical data shows that microbiological resistance of pneumococci to beta-lactams has very little influence on a possible failure of recommanded treatment regimens for pneumococcal pneumonia. The high rate of multiple drug resistance, particularly among beta-lactam resistant strains, rules out the probabilistic use of macrolides. Conversely, fluoroquinolone (FQ) resistance remains low, inferior to 3%, and the same is true for ketolides (<1%). Only a global strategy of patient management in the use of these new drugs could ensure their long-term activity. The high mortality rate of hospitalized S. pneumoniae pneumonia will only be improved with a better understanding of the complex host-bacteria interactions.

The quinolones: past, present, and future

The quinolone class of antimicrobial agents has generated considerable interest since its discovery >40 years ago. Substantial progress has been made in our understanding of the molecular mechanisms of the action of quinolones against pathogenic bacteria, the induction of resistance to quinolones in these organisms, and the potential of each quinolone compound to induce toxicity in treated patients. Here, these key discoveries are reviewed; the present indications approved by regulatory agencies are described in detail, with comments on adverse events caused by quinolones in treated patients; and speculation about the future of the quinolones is proffered, even though their future is difficult to predict, because many factors may affect their clinical usefulness. However, the emergence of bacterial resistance to the quinolones is a major factor that will determine the future clinical effectiveness of these agents, so that intense investigation of mechanisms to either prevent or curtail resistance to quinolones is of prime importance to their future.

Drug-resistant pneumococcal pneumonia: clinical relevance and approach to management

Community-acquired pneumonia is the most common infectious disease that causes death, with Streptococcus pneumoniae remaining the leading causative pathogen. The worldwide incidence of infections caused by pneumococci resistant to penicillin, macrolides, and other antimicrobial agents has increased at an alarming rate during the past 2 decades. Yet, these agents are still used as first-line empirical therapy in the outpatient setting. There are several reasons for this, including the infrequency of making a pathogen-specific diagnosis, the failure of studies to demonstrate the relevance of resistance, and the infrequency with which clinicians recognize clinical failures. Despite this, there is mounting evidence that supports the practice of using high doses of some antimicrobial agents, a more active antimicrobial agent within a class, or switching to another class of antimicrobial agents when a patient is identified as being at an increased risk of infection with a resistant pneumococcus. There is now information that will allow the physician to identify not only the patient at risk for infection with a resistant pneumococcus but also the antimicrobial class and, in some cases, the agent within the class to which the organism is more likely to be resistant. This will allow clinicians to better define optimal therapy for patients with community-acquired pneumonia.

Managing acute lower respiratory tract infections in an era of antibacterial resistance

Respiratory tract infections account for more than 116 million office visits and an estimated 3 million visits to hospital EDs annually. Patients presenting at EDs with symptoms suggestive of lower respiratory tract infections of suspected bacterial etiology are often severely ill, thus requiring a rapid presumptive diagnosis and empiric antimicrobial treatment. Traditionally, clinicians have relied on beta-lactam or macrolide antibiotics to manage community-acquired lower respiratory tract infections. However, the emerging resistance of Streptococcus pneumoniae to beta-lactams and/or macrolides may affect the clinical efficacy of these agents. Inappropriate use of antibiotics and use of agents with an overly broad spectrum of antimicrobial activity have contributed to the emergence of antibiotic resistance. When treating respiratory infections, clinicians need to prescribe antimicrobial agents only for those individuals with infections of suspected bacterial etiology; to select agents with a targeted spectrum of activity that ensures coverage against typical S pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis strains, including antibiotic-resistant strains and atypical pathogens; and to consider agents with specific chemical properties that limit the development of antimicrobial resistance and that achieve concentrations at sites of infection that exceed those required for bactericidal activity. Newer classes of antimicrobial agents, such as the oxazolidinones and ketolides, will likely play a significant role in this era of antimicrobial resistance.

Management of acute bacterial rhinosinusitis: current issues and future perspectives

Acute bacterial rhinosinusitis (ABRS), which manifests as an inflammation of at least one of the paranasal sinuses, is a major public health issue in developed countries. Diagnosis and treatment of ABRS can pose significant challenges in clinical practice, including difficulty in differentiation between viral and bacterial infection and a lack of simple, reliable and convenient methods for definitive diagnosis. Treatment choice is also a challenge because a decision is typically made empirically; therefore, the selection of therapy should be based on knowledge of local patterns of antimicrobial resistance, spectrum of activity against the most common ABRS pathogens (including those that are resistant to penicillins and macrolides) and pharmacodynamic potency. Current guidelines for diagnosis and treatment of ABRS in various countries share some similarities but also have important differences. Criteria for making the clinical diagnosis of sinusitis vary only slightly from country to country, while recommendations of therapy reflect the local impact of bacterial resistance.

Penicillins for Treatment of Pneumococcal Pneumonia: Does In Vitro Resistance Really Matter?

BACKGROUND

The rate of in vitro bacterial resistance to antimicrobial agents is escalating among pathogens that cause the most serious respiratory tract infections. Many reports published during the past few years suggest that this has direct clinical implications. In particular, resistance of Streptococcus pneumoniae to beta-lactam antibiotic therapy has assumed a prominent role in the evolution of guidelines for the initial treatment of respiratory tract infection.

METHODS

I conducted a critical review of the published medical literature.

RESULTS

There is only a single report of documented microbiologic failure of parenteral penicillin-class antibiotics in the treatment of pneumococcal pneumonia in patients with or without bacteremia, whereas there are numerous well-documented reports of treatment failure with quinolone-class (n > or = 21) and macrolide-class (n > or = 33) antibiotics in the treatment of pneumococcal pneumonia.

CONCLUSION

The recommended optimal in-hospital therapy for community-acquired pneumonia should continue to be a beta-lactam antibiotic (penicillin, aminopenicillin, cefotaxime, or ceftriaxone) administered with a macrolide or a fluoroquinolone agent for adjunctive treatment of infection with potential atypical pathogens.

Nosocomial pneumonia : rationalizing the approach to empirical therapy

Nosocomial pneumonia or hospital-acquired pneumonia (HAP) causes considerable morbidity and mortality. It is the second most common nosocomial infection and the leading cause of death from hospital-acquired infections. In 1996 the American Thoracic Society (ATS) published guidelines for empirical therapy of HAP. This review focuses on the literature that has appeared since the ATS statement. Early diagnosis of HAP and its etiology is crucial in guiding empirical therapy. Since 1996, it has become clear that differentiating mere colonization from etiologic pathogens infecting the lower respiratory tract is best achieved by employing bronchoalveolar lavage (BAL) or protected specimen brush (PSB) in combination with quantitative culture and detection of intracellular microorganisms. Endotracheal aspirate and non-bronchoscopic BAL/PSB in combination with quantitative culture provide a good alternative in patients suspected of ventilator-associated pneumonia. Since culture results take 2-3 days, initial therapy of HAP is by definition empirical. Epidemiologic studies have identified the most frequently involved pathogens: Enterobacteriaceae, Haemophilus influenzae, Streptococcus pneumoniae and Staphylococcus aureus ('core pathogens'). Empirical therapy covering only the 'core pathogens' will suffice in patients without risk factors for resistant microorganisms. Studies that have appeared since the ATS statement issued in 1996, demonstrate several new risk factors for HAP with multiresistant pathogens. In patients with risk factors, empirical therapy should consist of antibacterials with a broader spectrum. The most important risk factors for resistant microorganisms are late onset of HAP (>/=5 days after admission), recent use of antibacterial therapy, and mechanical ventilation. Multiresistant bacteria of specific interest are methicillin-resistant S. aureus (MRSA), Pseudomonas aeruginosa, Acinetobacter calcoaceticus-baumannii, Stenotrophomonas maltophilia and extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae. Each of these organisms has its specific susceptibility pattern, demanding appropriate antibacterial treatment. To further improve outcomes, specific therapeutic options for multiresistant pathogens and pharmacological factors are discussed. Antibacterials developed since 1996 or antibacterials with renewed interest (linezolid, quinupristin/dalfopristin, teicoplanin, meropenem, new fluoroquinolones, and fourth-generation cephalosporins) are discussed in the light of developing resistance.Since the ATS statement, many reports have shown increasing incidences of resistant microorganisms. Therefore, one of the most important conclusions from this review is that empirical therapy for HAP should not be based on general guidelines alone, but that local epidemiology should be taken into account and used in the formulation of local guidelines.

[Failure of levofloxacin therapy in two cases of community-acquired pneumonia caused by fluoroquinolone-resistant Streptococcus pneumoniae and complicated with empyema]

BACKGROUND

Community acquired pneumonia (CAP) due to Streptococcus pneumoniae is a frequent cause of morbidity and mortality. We communicate two cases of CAP with complications. In both cases levofloxacin-resistant S. pneumoniae was isolated in pleural effusion. Patient 1: A 51-year-old man who had not received previous treatment with quinolones was admitted to the hospital for CAP and initially treated with levofloxacin (500 mg/24h iv). Four days later pleural effusion developed and fluid culture isolated levofloxacin-resistant S. pneumoniae (MIC > 32 .g/ml). The outcome was favorable following chest tube placement and treatment with beta-lactam antibiotics. Patient 2: A 73-year-old man with a history of chronic obstructive pulmonary disease was admitted due to CAP and was initially treated with levofloxacin (500 mg/24 h iv). He was transferred to our hospital after 10 days of treatment with this antibiotic, following the development of pleural effusion with isolation of levofloxacin-resistant S. pneumoniae (MIC = 12 .g/ml). The patient was treated with chest tube placement and beta-lactam antibiotics with a favorable outcome.

CONCLUSIONS

Patients with CAP treated empirically must be closely followed, both clinically and radiologically, to facilitate early detection of complications due to bacterial resistance to the prescribed antibiotic. Patients with CAP who have received quinolones in the weeks before the development of pneumonia should not been treated empirically with these antibiotics because of the risk of resistance development.

A review of Streptococcus pneumoniae infection treatment failures associated with fluoroquinolone resistance

We reviewed all of the published reports of cases of fluoroquinolone treatment failures for respiratory tract infection due to fluoroquinolone-resistant Streptococcus pneumoniae. There were 20 ciprofloxacin and levofloxacin treatment failures reported. Physicians should be aware, when treating pneumococcal respiratory tract infections in older patients with a fluoroquinolone, that clinical failures might occur, especially for patients with comorbid illnesses and a history of recent fluoroquinolone use.

Comparative bacteriological efficacy of pharmacokinetically enhanced amoxicillin-clavulanate against Streptococcus pneumoniae with elevated amoxicillin MICs and Haemophilus influenzae

A new pharmacokinetically enhanced formulation of amoxicillin-clavulanate (2,000 mg of amoxicillin/125 mg of clavulanate twice a day; ratio 16:1) has been designed, with sustained-release technology, to allow coverage of bacterial strains with amoxicillin-clavulanic acid MICs of at least 4/2 mug/ml. The bacteriological efficacy of amoxicillin-clavulanate, 2,000/125 mg twice a day, ratio 16:1, was compared in a rat model of respiratory tract infection versus four other amoxicillin-clavulanate formulations: 8:1 three times a day (1,000/125 mg), 7:1 three times a day (875/125 mg), 7:1 twice a day (875/125 mg), and 4:1 three times a day (500/125 mg); levofloxacin (500 mg once a day); and azithromycin (1,000 mg on day 1 followed thereafter by 500 mg once a day). Bacterial strains included Streptococcus pneumoniae, with amoxicillin-clavulanic acid MICs of 2/1 (one strain), 4/2, or 8/4 microg/ml (three strains each), and Haemophilus influenzae, one beta-lactamase-positive strain and one beta-lactamase-negative, ampicillin-resistant strain. Animals were infected by intrabronchial instillation. Antibacterial treatment commenced 24 h postinfection, with doses delivered by computer-controlled intravenous infusion to approximate the concentrations achieved in human plasma following oral administration. Plasma concentrations in the rat corresponded closely with target human concentrations for all antimicrobials tested. Amoxicillin-clavulanate, 2,000/125 mg twice a day, ratio 16:1, was effective against all S. pneumoniae strains tested, including those with amoxicillin-clavulanic acid MICs of up to 8/4 microg/ml and against beta-lactamase-producing and beta-lactamase-negative ampicillin-resistant H. influenzae. These results demonstrate the bacteriological efficacy of pharmacokinetically enhanced amoxicillin-clavulanate 2,000/125 mg twice a day (ratio 16:1) against S. pneumoniae with amoxicillin-clavulanic acid MICs of at least 4/2 microg/ml and support clavulanate 125 mg twice a day as sufficient to protect against beta-lactamase in this rat model.

In vivo activity of gemifloxacin, moxifloxacin and levofloxacin against pneumococci with gyrA and parC point mutations in a sepsis mouse model measured with the all or nothing mortality end-point

A dose-decreasing immunocompetent sepsis mouse model was used to evaluate the in vivo effect of levofloxacin, moxifloxacin and gemifloxacin, using a ciprofloxacin/levofloxacin susceptible serotype 6B strain (ciprofloxacin MIC: 1 mg/l) and two resistant serotype 14 and 19F strains with gyrA and parC point mutations (ciprofloxacin MICs of 32 and 64 mg/l, respectively). Significant higher in vivo activity was found for moxifloxacin and gemifloxacin than for levofloxacin against strains 1 and 2, and for gemifloxacin versus moxifloxacin or levofloxacin against strain 3. Gemifloxacin treatment resulted in 100% survival against strains 1 and 2(AUC0-24 h/MIC of 30 and 62) but against strain 3, survival was 60-80% (AUC0-24 h/MIC of 93). Similar AUC0-24 h/MIC values produced different therapeutic results suggesting that in vitro parameters other than the MIC could influence efficacy predictions based on in vitro susceptibility tests (MICs) or pharmacodynamic parameters (AUC0-24 h/MIC).

Clonal dissemination of macrolide-resistant and penicillin-susceptible serotype 3 and penicillin-resistant Taiwan 19F-14 and 23F-15 Streptococcus pneumoniae isolates in Japan: a pilot surveillance study

Large-scale surveillance studies using molecular techniques such as pulsed-field gel electrophoresis (PFGE) have revealed that the spread of antibiotic-resistant pneumococci is due to clonal spread. However, in Japan, surveillance studies using such molecular techniques have never been done. Therefore, we conducted a pilot surveillance study to elucidate the present situation in Japan. Among the 145 isolates examined, the most prevalent serotype was type 19F (20%), for which most isolates were not susceptible to penicillin (86.2%) but were positive for the mef(A)/mef(E) gene (89.7%). The secondmost prevalent was serotype 3 (16.6%), for which most isolates were susceptible to penicillin (87.5%) and positive for the erm(B) gene (91.7%). PFGE analysis showed that both serotypes consisted mainly of clonally identical or related isolates and, in particular, 38% of the type 19F isolates were indistinguishable from or closely related to the Taiwan 19F-14 clone. In addition, some of the Japanese type 23F isolates with the erm(B) gene were indistinguishable from or related to the Taiwan 23F-15 clone as analyzed by PFGE. Based on the results of our pilot study performed in a single institution, it is likely that international antibiotic-resistant clones have already spread in Japan; therefore, a nationwide surveillance study should be urgently conducted.

Role of beta-lactam agents in the treatment of community-acquired pneumonia

Community-acquired pneumonia (CAP) is a common illness associated with high rates of morbidity and mortality worldwide. The beta-lactam antibacterial agents have been the mainstay of therapy for CAP for over four decades and remain as first-line therapy. However, the impact of the substantial prevalence of resistance seen among the common respiratory pathogens, particularly penicillin and macrolide resistance among Streptococcus pneumoniae, is now an area for concern. CAP treatment guidelines often recommend the use of a macrolide or fluoroquinolone in conjunction with, or as an alternative to, beta-lactam agents, but whether this is necessary is uncertain. This review outlines the historical use of beta-lactam antibacterial agents in the treatment of CAP along with their ongoing therapeutic utility.

Detection of resistance to gatifloxacin and moxifloxacin in Streptococcus pneumoniae with the VITEK 2 instrument

A group of 72 pneumococcal isolates resistant or intermediate to levofloxacin and 124 pneumococcal isolates susceptible to fluoroquinolones were tested by the VITEK 2 instrument using investigational test cards and by a broth microdilution reference method. The VITEK 2 instrument performed well, detecting 52 of 60 (86.7%) gatifloxacin-resistant isolates and 22 of 23 moxifloxacin-resistant isolates, and did not falsely classify any susceptible isolates as resistant.

Nonresponses and treatment failures with conventional empiric regimens in patients with community-acquired pneumonia

Although most patients with suspected CAP respond to empiric therapy,a small number of patients do not respond in the expected fashion. Age and underlying comorbid conditions have a strong influence on the course of illness. Less common causes of treatment failures include overwhelming infection, antimicrobial resistance, and misdiagnosis. It is a common practice for empiric antimicrobial treatment of CAP to be initiated without microbiologic studies. Clinicians carefully should observe these patients for unusual or slow responses and should be ready to pursue a more extensive search for the cause of treatment failure.

Levofloxacin versus ceftriaxone plus clarithromycin in the treatment of adults with community-acquired pneumonia requiring hospitalization

Consecutive adult patients admitted to the hospital with community-acquired pneumonia from January 2000 to September 2003 were included in this prospective observational cohort study. A total of 459 patients, 259 treated with levofloxacin in single drug therapy at a dose of 500 mg once a day and 209 with the combination of ceftriaxone plus clarithromycin at a dose of 2 g once a day and 500 mg every 12 h, respectively, were included. The hospital admission decision was made using a clinical guideline based on the Pneumonia Severity Index (PSI). Fifteen (6%) patients died in the group treated with levofloxacin in single drug therapy and 25 (12%) in the group treated with ceftriaxone plus clarithromycin (P = 0.024). The mortality differences between both treatment groups, adjusted by the PSI score, show an OR of 0.39 (95% CI 0.17-0.87). There were no statistically significant differences between the duration of treatments or hospital stay. These data suggest that levofloxacin as single drug therapy is more effective than the combination of ceftriaxone plus clarithromycin in the treatment of moderate to severe pneumonia that requires hospitalization.

Guide to selection of fluoroquinolones in patients with lower respiratory tract infections

Newer fluoroquinolones such as levofloxacin, moxifloxacin, gatifloxacin and gemifloxacin have several attributes that make them excellent choices for the therapy of lower respiratory tract infections. In particular, they have excellent intrinsic activity against Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis and the atypical respiratory pathogens. Fluoroquinolones may be used as monotherapy to treat high-risk patients with acute exacerbation of chronic bronchitis, and for patients with community-acquired pneumonia requiring hospitalisation, but not admission to intensive care. Overall, the newer fluoroquinolones often achieve clinical cure rates in > or =90% of these patients. However, rates may be lower in hospital-acquired pneumonia, and this infection should be treated on the basis of anticipated organisms and evaluation of risk factors for specific pathogens such as Pseudomonas aeruginosa. In this setting, an antipseudomonal fluoroquinolone may be used in combination with an antipseudomonalbeta-lactam. Concerns are now being raised about the widespread use, and possibly misuse, of fluoroquinolones and the emergence of resistance among S. pneumoniae, Enterobacteriaceae and P. aeruginosa. A number of pharmacokinetic parameters such as the peak concentration of the antibacterial after a dose (C(max)), and the 24-hour area under the concentration-time curve (AUC24) and their relationship to pharmacodynamic parameters such as the minimum inhibitory and the mutant prevention concentrations (MIC and MPC, respectively) have been proposed to predict the effect of fluoroquinolones on bacterial killing and the emergence of resistance. Higher C(max)/MIC or AUC24/MIC and C(max)/MPC or AUC24/MPC ratios, either as a result of dose administration or the susceptibility of the organism, may lead to a better clinical outcome and decrease the emergence of resistance, respectively. Pharmacokinetic profiles that are optimised to target low-level resistant minor subpopulations of bacteria that often exist in infections may help preserve fluoroquinolones as a class. To this end, optimising the AUC24/MPC or C(max)/MPC ratios is important, particularly against S. pneumoniae, in the setting of lower respiratory tract infections. Agents such as moxifloxacin and gemifloxacin with high ratios against this organism are preferred, and agents such as ciprofloxacin with low ratios should be avoided. For agents such as levofloxacin and gatifloxacin, with intermediate ratios against S. pneumoniae, it may be worthwhile considering alternative dose administration strategies, such as using higher dosages, to eradicate low-level resistant variants. This must, of course, be balanced against the potential of toxicity. Innovative approaches to the use of fluoroquinolones are worth testing in further in vitro experiments as well as in clinical trials.

Community-acquired pneumonia: new management strategies for evolving pathogens and antimicrobial susceptibilities

Community-acquired pneumonia (CAP) is still one of the leading causes of mortality and morbidity. The most common bacterial cause of CAP is Streptococcus pneumoniae. The increase in antimicrobial resistance has raised concerns about the efficacy of available therapies, and a call for the reassessment of both existing and newer therapeutic agents. Although microbiological breakpoints are useful for monitoring the emergence of resistance, the current National Committee for Clinical Laboratory Standards (NCCLS) guidelines make no distinction between clinical and microbiological breakpoints. Recent changes in NCCLS breakpoints for extended spectrum cephalosporins have provided a more meaningful approach to susceptibility testing and to consideration of the site of infection. Further controversy surrounds the clinical guidelines relating to CAP in terms of which antimicrobial agents should be given empirically to which types of patients. Within this review, the role of monotherapy versus the need for combination antimicrobial therapy, which often includes a macrolide and an extended spectrum cephalosporin such as ceftriaxone, is discussed. This review also discusses the various aspects of antimicrobial susceptibilities of S. pneumoniae, the drivers and influences of increasing resistance, the clinical relevance of this resistance and possible therapeutic options in the face of changing susceptibilities and mixed bacterial aetiologies. New guidelines from the IDSA attempt to embrace these changes.

Safety and efficacy of sequential i.v. to p.o. moxifloxacin versus conventional combination therapies for the treatment of community-acquired pneumonia in patients requiring initial i.v. therapy

To compare the efficacy of sequential i.v. to p.o. moxifloxacin with ceftriaxone +/- azithromycin +/- metronidazole for the treatment of patients with community acquired pneumonia (CAP), a multi-centered, prospective, randomized, open label study was performed. CAP patients were randomized to moxifloxacin (400 mg/d-at least one i.v. dose) or ceftriaxone (at least one dose of 2 g i.v. q.d. followed by cefuroxime 500 mg p.o. b.i.d.) +/- azithromycin, +/- metronidazole (cephalosporin/macrolide control: CMC). The primary endpoint was clinical response at test-of-cure (TOC) visit. Bacteriological response at TOC was the secondary endpoint. Clinical cure was found in 83.3% (90/108) of moxifloxacin patients and 79.6% (90/113) of control patients. Microbiological responses were 81.8% (18/22) for moxifloxacin and 60.7% (17/28) for CMC patients. Drug-related adverse events occurred in 18.0% of moxifloxacin and 16% of CMC patients. It is concluded that i.v. to p.o. moxifloxacin is as effective as CMC for treatment of CAP and is a reliable alternative antimicrobial therapy.

In vitro antimicrobial susceptibilities of Streptococcus pneumoniae clinical isolates obtained in Canada in 2002

Empirical treatment is best guided by current surveillance of local resistance patterns. The goal of this study is to characterize the prevalence of antimicrobial nonsusceptibility within pneumococcal isolates from Canada. The Canadian Bacterial Surveillance Network is comprised of laboratories from across Canada. Laboratories collected a defined number of consecutive clinical and all sterile site isolates of S. pneumoniae in 2002. In vitro susceptibility testing was performed by broth microdilution with NCCLS guidelines. Rates of nonsusceptibility were compared to previously published reports from the same network. A total of 2,539 isolates were tested. Penicillin nonsusceptibility increased to 15% (8.5% intermediate, 6.5% resistant) compared to 12.4% in 2000 (P < or = 0.025, chi(2)). Only 32 (1.3%) isolates had an amoxicillin MIC of > or = 4 microg/ml and only 2 of 32 cerebrospinal fluid isolates had an intermediate susceptibility to ceftriaxone by meningeal interpretive criteria (MIC = 1 microg/ml). A total of 354 (13.9%) isolates were macrolide nonsusceptible (46.3% MLS(B), 56.7% M phenotype), increasing from 11.4% in 2000 (P < or = 0.0075, chi(2)). Only 13 (<1%) isolates had a telithromycin MIC of >1 microg/ml. Ciprofloxacin nonsusceptibility (defined as an MIC of > or = 4 microg/ml) increased to 2.7% compared to 1.4% in 2000 (P < or = 0.0025, chi(2)) and was primarily found in persons > or =18 years old (98.5%). Nonsusceptibility to penicillin, macrolides, and fluoroquinolones is increasing in Canada. Nonsusceptibility to amoxicillin and ceftriaxone remains uncommon. Newer antimicrobials such as telithromycin and respiratory fluoroquinolones have excellent in vitro activity.

Streptococcus pneumoniae and community-acquired pneumonia: a cause for concern

Community-acquired pneumonia (CAP) is the sixth most common cause of death in the United States and the leading cause of death from infectious diseases. It is associated with significant morbidity and mortality, and poses a major economic burden to the healthcare system. Streptococcus pneumoniae is the leading cause of CAP. Other common bacterial causes include Haemophilus influenzae as well as atypical bacteria (Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella species). Increasing resistance to a variety of antimicrobial agents has been documented in S. pneumoniae and is common in H. influenzae as well. Successful empiric therapy is paramount to the management of CAP to avoid treatment failure and subsequent associated costs. Given that resistance is increasing among respiratory pathogens, and S. pneumoniae is the most common etiologic agent identified in CAP, strategies for antimicrobial therapy should be based on the likely causative pathogen, the presence of risk factors for infection with resistant bacteria, and local resistance patterns.

Application of pharmacokinetics and pharmacodynamics to antimicrobial therapy of respiratory tract infections

The pharmacologic field that studies antimicrobial pharmacokinetics and pharmacodynamics (PK/PD) has had a major impact on the choice and dosing regimens used for many antibiotics especially those used in the treatment of respiratory tract infections. PK/PD parameters are particularly important in light of increasing antimicrobial resistance. Drug pharmacokinetic features, such as serum concentrations over time and area under the concentration-time curve, when integrated with minimum inhibitory concentration (MIC) values of antibiotics against pathogens, can predict the probability of bacterial eradication and clinical success. These pharmacokinetic and pharmacodynamic relationships also are important in preventing the selection and spread of resistant strains and have led to the description of the mutation prevention concentration, which is the lowest concentration of antimicrobial that prevents selection of resistant bacteria from high bacterial inocula. b-lactams are time-dependent agents without significant post-antibiotic effects, resulting in bacterial eradication when unbound serum concentrations exceed MICs of these agents against infecting pathogens for >40% to 50% of the dosing interval. Macrolides, azaolides, and lincosamides are time-dependent agents with prolonged post-antibiotic effects, and fluoroquinolones are concentration-dependent agents, resulting in both cases in bacterial eradication when unbound serum area-under-the-curve to MIC ratios exceed 25 to 30. These observations have led to changes in recommended antimicrobial dosing against respiratory pathogens and are used to assess the role of current agents, develop new formulations, and assess potency of new antimicrobials.

Quinolone Resistance among Pneumococci: Therapeutic and Diagnostic Implications

Fluoroquinolones are widely recommended as empirical monotherapy for community-acquired pneumonia. Since 1999, case reports of failure of levofloxacin therapy due to levofloxacin-resistant strains of Streptococcus pneumoniae have started to appear. Most worrying is that, in some cases, levofloxacin resistance has been acquired by pneumococci within days of the initiation of therapy. Because use of current clinical antimicrobial resistance breakpoints fail to identify the majority of S. pneumoniae isolates with only first-step mutations, current treatment guidelines not only may have implications with regard to the ability of surveillance programs to detect emerging resistance but may have therapeutic implications as well.

Clinical relevance of antimicrobial resistance in the management of pneumococcal community-acquired pneumonia

Streptococcus pneumoniae remains the most common bacterial cause of community-acquired pneumonia, and these infections are associated with significant morbidity and mortality worldwide. A major concern is the increasing incidence of antibiotic resistance among pneumococcal isolates, which, in the case of certain of the antibiotic classes, has been associated with treatment failure. Yet despite multiple reports of infections with penicillin-resistant pneumococcal isolates, no cases of bacteriologic failure have been documented with the use of penicillin or ampicillin in the treatment of pneumonia caused by penicillin-resistant pneumococci. Current prevalence and levels of penicillin resistance among pneumococal isolates in most areas of the world do not indicate a need for substantial treatment changes with regard to the use of the penicillins. For infections with penicillin-sensitive strains, penicillin or an aminopenicillin in a standard dosage will still be effective for treatment. In the cases of strains with intermediate resistance, beta-lactam agents are still considered appropriate treatment, although higher dosages are recommended. Infections with isolates of high-level penicillin resistance should be treated with alternative agents such as the third-generation cephalosporins or the new antipneumococcal fluoroquinolones. In the case of the cephalosporins, pharmacodynamic/pharmacokinetic parameters help predict which of those agents are likely to be successful, and the less active agents should not be used. Debate continues in the literature with regard to the impact of macrolide resistance on the outcome of pneumococcal pneumonia, with some investigators providing evidence of an "in vivo-in vitro paradox," referring to discordance between reported in vitro resistance and clinical success of macrolides/azalide in vivo. However, several cases of macrolide/azalide treatment failure have been documented, and many clinicians recommend that these agents not be used on their own in areas with a high prevalence and levels of macrolide/azalide resistance. However, evidence is emerging to show beneficial effects on outcome with combination therapy, especially that of a beta-lactam agent and a macrolide given together to sicker, hospitalized patients with pneumococcal pneumonia. In an attempt to prevent the emergence of resistance, it has been recommended by some that the new fluoroquinolones not be used routinely as first-line agents in the treatment of community-acquired pneumonia; instead, they say, these agents should be reserved for patients who are allergic to the commonly used beta-lactam agents, for infections known to be or suspected of being caused by highly resistant strains, and for patients in whom initial therapy has failed.

Guidelines for Empiric Antimicrobial Prescribing in Community-Acquired Pneumonia

Empiric antimicrobial prescribing for community-acquired pneumonia remains a challenge, despite the availability of treatment guidelines. A number of key differences exist between North American and European guidelines, mainly in the outpatient setting. The North American approach is to use initial antimicrobial therapy, which provides coverage for Streptococcus pneumoniae plus atypical pathogens. Europeans tend to focus on providing pneumococcal coverage with less emphasis on covering for an atypical pathogen. Ambulatory patients without comorbidity are more likely to receive macrolide therapy in North America, whereas in Europe these patients would probably receive a beta-lactam agent. Major issues that are fundamental to this difference include the importance of providing therapy for atypical pathogens and the clinical significance of macrolide-resistant S pneumoniae. Prospective data are required to evaluate which of these two approaches offers clinical superiority.

Pharmacodynamics of moxifloxacin and levofloxacin at simulated epithelial lining fluid drug concentrations against Streptococcus pneumoniae

Recent clinical failures associated with levofloxacin treatment for Streptococcus pneumoniae infections and growing evidence of frequent mutations in the isolate population have led to increased concerns regarding fluoroquinolone resistance. Our objective was to characterize the efficacies of levofloxacin and moxifloxacin against various genotypes of S. pneumoniae after simulated bronchopulmonary exposures. An in vitro model was used to simulate a levofloxacin concentration of 500 mg and a moxifloxacin concentration of 400 mg, which were previously determined to be the concentrations in the epithelial lining fluid of older adults receiving once-daily dosing. The effects of the drugs were tested against six S. pneumoniae containing various mutations. Bacterial density and resistance were quantitatively assessed over 48 h. The S. pneumoniae isolate with no mutation displayed a 4-log reduction in CFU after treatment with both agents and did not develop resistance. Isolates containing the parC or parE mutation or both mutations regrew and developed resistance when they were exposed to levofloxacin, despite an unbound area under the concentration-time curve (AUC):MIC ratio of approximately 100. When the isolate containing the parC and gyrA mutations was exposed to levofloxacin, there was a half-log reduction in the number of CFU compared to that for the control, but the isolate subsequently regrew. Likewise, levofloxacin did not kill the isolate containing the parC, gyrA, and parE mutations. Moxifloxacin sustained the killing of all bacterial isolates tested without the development of resistance. Levofloxacin did not sustain bacterial killing and did not prevent the emergence of further resistance in mutants with the parC or parE mutation or both mutations, even though an unbound AUC:MIC ratio for exposure well above the breakpoint of 30 to 40 established in the literature for S. pneumoniae was maintained. Moxifloxacin was effective against all isolates tested, despite the presence of isolates with two- and three-step mutations, for which the MICs were increased.

In vitro pharmacodynamic activities of ABT-492, a novel quinolone, compared to those of levofloxacin against Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis

ABT-492 is a novel quinolone with potent activity against gram-positive, gram-negative, and atypical pathogens, making this compound an ideal candidate for the treatment of community-acquired pneumonia. We therefore compared the in vitro pharmacodynamic activity of ABT-492 to that of levofloxacin, an antibiotic commonly used for the treatment of pneumonia, through MIC determination and time-kill kinetic analysis. ABT-492 demonstrated potent activity against penicillin-sensitive, penicillin-resistant, and levofloxacin-resistant Streptococcus pneumoniae strains (MICs ranging from 0.0078 to 0.125 micro g/ml); beta-lactamase-positive and beta-lactamase-negative Haemophilus influenzae strains (MICs ranging from 0.000313 to 0.00125 micro g/ml); and beta-lactamase-positive and beta-lactamase-negative Moraxella catarrhalis strains (MICs ranging from 0.001 to 0.0025 micro g/ml), with MICs being much lower than those of levofloxacin. Both ABT-492 and levofloxacin demonstrated concentration-dependent bactericidal activities in time-kill kinetics studies at four and eight times the MIC with 10 of 12 bacterial isolates exposed to ABT-492 and with 12 of 12 bacterial isolates exposed to levofloxacin. Sigmoidal maximal-effect models support concentration-dependent bactericidal activity. The model predicts that 50% of maximal activity can be achieved with concentrations ranging from one to two times the MIC for both ABT-492 and levofloxacin and that near-maximal activity (90% effective concentration) can be achieved at concentrations ranging from two to five times the MIC for ABT-492 and one to six times the MIC for levofloxacin.

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 2: Human Trials

OBJECTIVE

To review clinical trials with fluoroquinolones and the pharmacokinetic and pharmacodynamic parameters predictive of clinical and microbiologic outcomes and resistance. Data on fluoroquinolones are summarized and the premise that a single AUIC target >125 may be used for all fluoroquinolones against all target organisms is examined.

DATA SOURCES

Primary articles were identified by a 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 upon concentrations achieved and outcomes depend upon 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 (Part 1), 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 human trials favors the use of AUIC values >250 for rapid bactericidal action, regardless of whether the organism is gram-negative or gram-positive.

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.

Activities of mutant prevention concentration-targeted moxifloxacin and levofloxacin against Streptococcus pneumoniae in an in vitro pharmacodynamic model

The differential effects of moxifloxacin and levofloxacin on the development of resistance in four Streptococcus pneumoniae isolates were examined by using an in vitro pharmacodynamic model. Therapeutic regimens (moxifloxacin: peak, 4.5 micro g/ml; half-life [t(1/2)], 12 h; and levofloxacin: peak, 6 micro g/ml; t(1/2), 6 h) were tested against two fluoroquinolone-susceptible isolates (strains 79 and ATCC 49619) and KD2138 and KD2139 (parC and gyrA mutants, respectively, of ATCC 49619). Mutant prevention concentration (MPC)-targeted regimens with modified pharmacokinetics of each drug were simulated to match the area under the concentration-time curve (AUC) above the MPC for the two fluoroquinolones. Moxifloxacin MICs and MPCs (MIC/MPC) for isolates 79, ATCC 49619, KD2138, and KD2139, respectively, were 0.125 and 0.5, 0.125 and 0.5, 0.25 and 8, and 0.25 and 4 micro g/ml. Levofloxacin MICs and MPCs for the same isolates were 1 and 4, 0.5 and 2, 1 and 64, and 0.5 and 32 micro g/ml, respectively. Therapeutic levofloxacin concentrations led to isolation of mutants of ATCC 49619 (S79Y in ParC), KD2138 (S81Y in GyrA), and KD2139 (S79Y in ParC). Therapeutic moxifloxacin concentrations against the gyrA mutant KD2139 resulted in outgrowth of a mutant with a ParC substitution (S79Y) but caused no emergence of mutants of the other three isolates. MPC-targeted moxifloxacin (lower-than-normal peak = 0.75 to 1.5 micro g/ml, administered at levofloxacin's t(1/2)) caused growth of a GyrA variant (S81Y) of KD2138 and a ParC variant (S79Y) of KD2139, while no mutants of ATCC 49619 were recovered. MPC-targeted levofloxacin (higher-than-normal peak = 14.5 to 29.5 micro g/ml, administered at moxifloxacin's t(1/2)) against KD2138 and KD2139 did not prevent the development of the mutations observed in therapeutic regimens, but resistance in the fluoroquinolone-susceptible ATCC 49619 was no longer noted. Normalization of the respective AUC/MPC ratios of moxifloxacin and levofloxacin did not eliminate differences in resistance selectivity of the two agents in all cases. We conclude that the reduced recovery of resistant mutants of S. pneumoniae following moxifloxacin exposure compared to levofloxacin may be due to intrinsic differences between the drugs. Increasing the concentration and exposure (t(1/2)) to exceed the MPC may prevent mutations from occurring in fluoroquinolone-susceptible strains. However, this strategy did not prevent the selection of secondary mutants in strains with preexisting mutations. Further study of the MPC concept to evaluate these relationships is warranted.

Worldwide trends in antimicrobial resistance among common respiratory tract pathogens in children

BACKGROUND

Respiratory tract infections among children are a common reason for health care provider visits and the primary reason for antimicrobial prescribing in this population. The increased prevalence of resistance among Streptococcus pneumoniae and Haemophilus influenzae pathogens poses a serious challenge in the successful treatment of respiratory tract infections caused by these pathogens.

METHODS

This paper reviews worldwide trends in antimicrobial resistance among common respiratory tract pathogens, highlighting data obtained from the pediatric population where available.

RESULTS

S. pneumoniae resistance to beta-lactams is mediated through alterations in the penicillin-binding proteins and macrolide resistance to acquisition of efflux or methylation genes. The mechanisms of resistance to the fluoroquinolones include target enzyme alterations via genetic mutations and transport out of the bacterial cell via an efflux pump. Beta-lactamase production is the primary mechanism of resistance to penicillins among H. influenzae isolates. Although S. pneumoniae with reduced susceptibility to penicillin was first documented > 30 years ago, resistance has increased at an alarming rate worldwide in the past decade. According to recent surveillance data, the worldwide prevalence of S. pneumoniae with reduced susceptibility to penicillin is 18.2%. Beta-lactamase production among H. influenzae ranges from approximately 4% in Russia to 26% in the United States and to 31% in France. The prevalence of beta-lactamase-negative, ampicillin-resistant H. influenzae remains very low (< 1%) worldwide, except in Japan, where the incidence is higher. In general, the highest rates of resistance are observed in isolates obtained from children, and risk factors for infection with a resistant pathogen include young age, the site of infection, day-care center attendance and recent antimicrobial use.

CONCLUSIONS

Increased prevalence of antimicrobial resistance among respiratory tract pathogens isolated from children and adults is evident worldwide. Treatment of infections caused by S. pneumoniae and H. influenzae with older agents or ineffective dosing regimens may not eradicate infections and may contribute to the spread of resistance. These observations confirm the need for appropriate antimicrobial use to halt or at least limit the spread of resistance.

Emergence of levofloxacin-resistant pneumococci in immunocompromised adults after therapy for community-acquired pneumonia

We describe 4 patients infected with levofloxacin-resistant pneumococci after therapy for community-acquired pneumonia (CAP). The 4 patients had 15 episodes of CAP; Streptococcus pneumoniae was isolated from blood or sputum samples obtained during 14 of the episodes. The underlying medical condition was Bruton agammaglobulinemia in 3 patients and chronic lymphoid leukemia in the other. The initial episode of CAP in each patient was due to a levofloxacin-susceptible strain. One of 4 reinfections and 5 of 6 relapses were due to levofloxacin-resistant strains. All of these strains had amino acid substitutions in the quinolone-resistance-determining region of the genes parC and gyrA. The time between episodes of pneumonia varied from 1 to 4 months. In immunocompromised patients with suspected or proven pneumococcal infection, it may be prudent not to use fluoroquinolone monotherapy empirically when the patient has a history of fluoroquinolone therapy in at least the past 4 months.

Telithromycin- and fluoroquinolone-resistant Streptococcus pneumoniae in Taiwan with high prevalence of resistance to macrolides and beta-lactams: SMART program 2001 data

There is a high prevalence of beta-lactam- and macrolide-resistant Streptococcus pneumoniae in Taiwan. To understand the in vitro susceptibilities of recent isolates of S. pneumoniae to fluoroquinolones and telithromycin (which is not available in Taiwan), the MICs of 23 antimicrobial agents for 936 clinical isolates of S. pneumoniae isolated from different parts of Taiwan from 2000 to 2001 were determined by the agar dilution method. Overall, 72% of isolates were not susceptible to penicillin (with 61% being intermediate and 11% being resistant) and 92% were resistant to erythromycin. Telithromycin MICs were >or=1 microg/ml for 16% of the isolates, and for 99% of these isolates the MICs of all macrolides tested were >or=256 microg/ml; all of these isolates had the constitutive macrolide-lincosamide-streptogramin B phenotype. Eighty-eight percent of the isolates were resistant to three or more classes of drugs. The ciprofloxacin MICs were >or=4 microg/ml for six (0.6%) isolates from five patients collected in 2000 and 2001, and the levofloxacin MICs were >or=8 microg/ml for five of these isolates. Seven isolates for which ciprofloxacin MICs were >or=4 microg/ml, including one isolate recovered in 1999, belonged to three serotypes (serotype 19F, five isolates; serotype 23A, one isolate; and serotype 23B, one isolate). The isolates from the six patients for which ciprofloxacin MICs were >or=4 microg/ml had different pulsed-field gel electrophoresis profiles and random amplified polymorphic DNA patterns, indicating that no clonal dissemination occurred over this time period. Despite the increased rate of fluoroquinolone use, the proportion of pneumococcal isolates for which ciprofloxacin MICs were elevated (>or=4 microg/ml) remained low. However, the occurrence of telithromycin resistance is impressive and raises concerns for the future.