A critical review of the fluoroquinolones: focus on respiratory infections

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.

Moxifloxacin: a review of its use in the management of bacterial infections

Moxifloxacin (Avelox) is a fluoroquinolone antibacterial with a methoxy group in the C-8 position and a bulky C-7 side chain. Moxifloxacin is approved for use in the treatment of acute exacerbations of chronic bronchitis (AECB), community-acquired pneumonia (CAP), acute bacterial sinusitis and uncomplicated skin and skin structure infections (approved indications may differ between countries). Moxifloxacin has a broad spectrum of antibacterial activity, including activity against penicillin-resistant Streptococcus pneumoniae. It achieves good tissue penetration and has a convenient once-daily administration schedule, as well as being available in both intravenous and oral formulations in some markets. Moxifloxacin has good efficacy in the treatment of patients with AECB, CAP, acute bacterial sinusitis and uncomplicated skin and skin structure infections, and is generally well tolerated. Thus, moxifloxacin is an important option in the treatment of bacterial infections.

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.

Short-Course Antimicrobial Therapy for Community-Acquired Pneumonia

Management of community-acquired pneumonia (CAP) remains surprisingly controversial. Optimal duration of antimicrobial therapy reflects one of the open questions due to the lack of sufficient randomized clinical trial data. Recently, there have been efforts to rationalize antimicrobial therapy of this disease. Trials addressing the issue of short-course antimicrobial therapy for CAP have revealed no adverse outcomes with a treatment duration of 5 days when compared with conventional courses of 7-10 days. There is accumulating evidence that a shorter duration of antimicrobial therapy may have benefits in patients with CAP, as it might enhance compliance, decrease the development of antimicrobial resistance, decrease the incidence and shorten the duration of adverse drug effects, reduce treatment costs and improve patient satisfaction with therapy. Nevertheless, remaining questions regarding the influence of patient selection, disease severity or choice of antimicrobial for short-course therapy indicate the need for further randomized controlled clinical trials in this area of research. This article summarizes current evidence for short-course therapy in patients with CAP and draws conclusions for clinical practice.

Mutant prevention concentrations for single-step fluoroquinolone-resistant mutants of wild-type, efflux-positive, or ParC or GyrA mutation-containing Streptococcus pneumoniae isolates

Three fluoroquinolone-susceptible and five fluoroquinolone-resistant (two with ParC Ser79Phe mutations, one with a GyrA Ser81Phe mutation, and two that were efflux positive) Streptococcus pneumoniae isolates were exposed to one, two, four, eight, and sixteen times the MICs of ciprofloxacin, gatifloxacin, gemifloxacin, levofloxacin, and moxifloxacin. Mutational frequencies were calculated at each multiple of the MIC for which growth was observed. Mutant prevention concentrations (MPCs) and the multiple of the MIC at the MPC (MP(MIC)) were evaluated. All resulting mutants were sequenced for quinolone resistance-determining region changes in GyrA and ParC and were evaluated for reserpine-sensitive efflux. The MPC order was generally ciprofloxacin > levofloxacin > gatifloxacin > moxifloxacin > gemifloxacin. The MP(MIC) order varied depending on the genetic constitution of the original isolates from which the mutants were generated. For those mutants created from fluoroquinolone-susceptible isolates (those that had wild-type ParC and GyrA and were efflux negative), the MP(MIC) order was ciprofloxacin = moxifloxacin > gemifloxacin > levofloxacin > gatifloxacin. The MP(MIC)s of each fluoroquinolone for mutants created from isolates with a ParC mutation (with wild-type GyrA and efflux negative) were similar. A similar occurrence was observed with the mutants created from the efflux-positive isolates (with wild-type ParC and GyrA). The MP(MIC) order for the mutants created from the isolate with a GyrA mutation (with wild-type ParC and efflux negative) was ciprofloxacin = gemifloxacin > levofloxacin = moxifloxacin > gatifloxacin. Gatifloxacin, levofloxacin, and moxifloxacin may be intrinsically more able to prevent the development of resistance by fluoroquinolone-susceptible isolates, isolates that are efflux positive, or isolates that carry a GyrA mutation. However, once a ParC mutation is present, the MPC increases dramatically for all fluoroquinolones.

In vitro Antimicrobial Activity of Gatifloxacin Compared with Other Quinolones against Clinical Isolates from Cancer Patients

Owing to the predominance of gram-positive pathogens in neutropenic cancer patients, newer generation quinolones with an expanded gram-positive spectrum and enhanced potency, may have a role to play for prophylaxis and/or empiric therapy in such patients. The in vitro activity of gatifloxacin was compared with that of ciprofloxacin, levofloxacin and trovafloxacin against 848 recent clinical isolates from cancer patients. Against gram-positive organisms, gatifloxacin was the most active agent tested inhibiting all Aerococcus, Listeria monocytogens, Micrococcus, Stomatococcus mucilaginous, Bacillus, and Rhodococcus equi strains at < or =2 mg/l, its designated susceptibility breakpoint. It was also very active against methicillin-susceptible staphylococci and Streptococcus spp. (including penicillin nonsusceptible Streptococcus pneumoniae and viridans streptococci). It had moderate activity against methicillin-resistant staphylococci and Enterococcus faecalis, inhibiting 68-80% of these strains at < or =2 mg/l. Gatifloxacin also had good activity against the Enterobacteriaceae (although ciprofloxacin was more potent) inhibiting >95% of isolates at < or =1 mg/l. Nonfermentative gram-negative organisms were less susceptible to all 4 agents. Gatifloxacin was very active against Acinetobacter lwoffi (MIC100 0.12 mg/l) and had moderate activity against Acinetobacter baumanii, Chryseobacterium spp., Stenotrophomonas maltophilia, Pseudomonas aeruginosa and other Pseudomonas species. Alcaligenes xylosoxidans strains were relatively resistant to all 4 agents.

Designing fluoroquinolone breakpoints for Streptococcus pneumoniae by using genetics instead of pharmacokinetics-pharmacodynamics

We determined fluoroquinolone microbiological resistance breakpoints for Streptococcus pneumoniae by using genetic instead of pharmacokinetic-pharmacodynamic parameters. The proposed microbiological breakpoints define resistance as the MIC at which >50% of the isolates carry quinolone resistance-determining region mutations and/or, if data are available, when Monte Carlo simulations demonstrate a <90% chance of bacteriological eradication. The proposed microbiological resistant breakpoints are as follows (in micrograms per milliliter): gatifloxacin, >0.25; gemifloxacin, >0.03; levofloxacin, >1; and moxifloxacin, >0.12. Monte Carlo simulations of the once daily 400-mg doses of gatifloxacin and 750-mg doses levofloxacin demonstrated a high level of target attainment (free-drug area under the concentration-time curve from 0 to 24 h/MIC ratio of 30) by using these new genetically derived breakpoints.

Pharmacokinetics of moxifloxacin in patients undergoing continuous venovenous haemodiafiltration

OBJECTIVE

Moxifloxacin is an 8-methoxy quinolone with a broad range of activity against clinically important pathogens. Therefore it is frequently administered in severe respiratory tract infections. Continuous venovenous haemodiafiltration (CVVHDF) is an important extracorporeal renal replacement therapy for intensive care patients suffering from sepsis and multiple organ failure. The aim of this study was to investigate the pharmacokinetics of intravenous moxifloxacin in anuric critically ill patients undergoing CVVHDF.

PATIENTS AND METHODS

Pharmacokinetic analysis was performed in nine intensive care patients with acute renal failure and suspected or proven infection sensitive to moxifloxacin, who received moxifloxacin 400 mg intravenously once daily. The concentration of moxifloxacin in serum and ultradiafiltrate was determined by HPLC.

RESULTS

Peak and trough serum concentrations were 3.76 +/- 2.02 mg/L and 0.24 +/- 0.14 mg/L, respectively, at the arterial port after the first dose. The mean elimination half-life was 9.87 +/- 3.26 h, the volume of distribution 270 +/- 133 L and the calculated AUC0-24 18.41 +/- 8.46 mg.h/L. Total clearance was 19.09 +/- 8.22 L/h and the clearance of haemodiafiltration 1.63 +/- 0.33 L/h.

CONCLUSIONS

The pharmacokinetics of moxifloxacin in critically ill patients with acute renal failure undergoing CVVHDF was comparable to healthy subjects and patients without renal impairment. We recommend 400 mg of intravenous moxifloxacin once per day in anuric patients during CVVHDF.

Antimicrobial susceptibility of Streptococcus pneumoniae in Latin America: results from five years of the SENTRY Antimicrobial Surveillance Program

A total of 1561 pneumococcal isolates were collected in 1997-2001, mainly from patients with community-acquired respiratory tract infections, and susceptibilities were tested by reference broth microdilution against 29 antimicrobial agents. In general, 69.3% of strains were considered susceptible (MIC < or = 0.06 mg/L) to penicillin. Resistance to penicillin (MIC > or = 2 mg/L) and cefotaxime (MIC > or = 4 mg/L) was found in 11.9% and 0.4% of isolates, respectively. The fluoroquinolones gatifloxacin (MIC90, 0.5 mg/L) and levofloxacin (MIC90, 1 mg/L) were active against > 99% of the isolates tested. Among the other non-beta-lactam drugs tested, the rank order of susceptibility was chloramphenicol (95.6%) > clindamycin (94.5%) > azithromycin (88.5%) > clarithromycin (87.5%) >tetracycline (79.5%) > trimethoprim + sulphamethoxazole (60.5%). The penicillin-non-susceptible isolates presented higher rates of resistance to other antimicrobial agents. The rank order of penicillin resistance rates among the seven participating countries was Mexico (25.0%) > Uruguay (19.2%) > Chile (18.3%) > Colombia = Argentina (9.9%) > Brazil (3.9%) > Venezuela (2.8%). The regional rate of penicillin resistance did not vary significantly over the years studied (p 0.339). Screening for the ermB and mefA genes by multiplex rapid cycle PCR on 23 erythromycin-resistant isolates collected during the year 2001 showed that 43.5% and 56.5%, respectively, were positive for ermB and mefA. Overall, the results indicated that antimicrobial susceptibilities of Streptococcus pneumoniae vary significantly among Latin American countries. Regional and local surveillance programmes are necessary to guide empirical therapy of pneumococcal infection in Latin American countries.

Impact of Ketolides on Resistance Selection and Ecologic Effects during Treatment for Respiratory Tract Infections

Ketolides are a new class of antibacterials that have been specifically developed for the treatment of community-acquired respiratory tract infections in an era of increasing resistance among major etiologic pathogens. These agents possess several unique structural features, including a 3-keto function and a large aromatic side chain, that confer not only a mode of action that differentiates them from the macrolide class but also a reduced potential to induce--or select for--resistant strains. Studies also suggest that ketolides such as telithromycin have a lower ecologic impact on the body's microflora than agents such as clarithromycin and amoxicillin-clavulanate, potentially reducing the risk of emergence of resistant strains and the spread of such resistance to pathogenic species. Therefore, available evidence suggests that ketolides may not only provide important new treatment options in an era of increasing resistance but may also contribute to reducing the pressure for development of further resistance. Clearly, further studies are required to confirm this low resistance potential once the ketolide agents become more widely used in routine practice.

Gemifloxacin: a new fluoroquinolone approved for treatment of respiratory infections

OBJECTIVE

To evaluate the microbiology, pharmacokinetic parameters, drug interactions, and results of the available clinical trials of gemifloxacin for the treatment of community-acquired pneumonia (CAP) and acute exacerbation of chronic bronchitis (AECB).

DATA SOURCES

MEDLINE (1966-September 2003) was searched for primary and review articles. Data from the manufacturer were also included. Key words included adverse effects, clinical trials, drug interactions, gemifloxacin, and pharmacokinetic parameters.

STUDY SELECTION AND DATA EXTRACTION

All articles and product labeling concerning gemifloxacin, a fluoroquinolone antibiotic recently approved by the Food and Drug Administration for treatment of CAP and AECB, were included for review.

DATA SYNTHESIS

Compared with currently available fluoroquinolones, gemifloxacin demonstrated improved in vitro activity against Streptococcus pneumoniae (minimum inhibitory concentration for 90% eradication 0.03 microg/mL) and similar activity against gram-negative respiratory pathogens (Haemophilus influenzae, Moraxella catarrhalis) and atypical pathogens such as Chlamydia pneumoniae, Legionella pneumophila, and Mycoplasma pneumoniae. Gemifloxacin, consistent with other available fluoroquinolones, has insufficient activity against methicillin-resistant Staphylococcus aureus to allow clinical use for such infections. Gemifloxacin has adequate bioavailability and a favorable drug interaction profile. Gemifloxacin was comparable to commonly employed nonfluoroquinolone regimens for treatment of CAP and AECB, although the studies were designed to demonstrate equivalence. Gemifloxacin once daily for 5-7 days was well tolerated in controlled and uncontrolled clinical studies. Available clinical data, however, are insufficient to draw clinical or toxicologic distinctions between gemifloxacin and other fluoroquinolones.

CONCLUSIONS

Gemifloxacin may be a suitable choice for empiric treatment of CAP or AECB. However, due to the significant history of fluoroquinolone-induced hepatic failure and dermatologic complications, the use of this drug should be closely monitored.

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.

Antibiotics and collateral damage

The precarious stability of the normal indigenous flora of the human gastrointestinal tract may be disturbed by a number of factors, but frequently and crucially by antibiotic therapy. This article explores recent insights on the collateral and ecologic effects of antibiotics on the microbiologic flora of the human body and the possible consequences of those effects, which are just beginning to be better understood. New data on this subject will not only help in designing better clinical trials but also begin to answer key questions about collateral damage.

Monotherapy versus Dual Therapy for Community-Acquired Pneumonia in Hospitalized Patients

Several medical-specialty professional societies have suggested that combination therapy with a beta -lactam plus a macrolide or doxycycline or monotherapy with a "respiratory quinolone" (i.e., levofloxacin, gatifloxacin, moxifloxacin, or gemifloxacin) are optimal first-line therapy for patients hospitalized with community-acquired pneumonia. These recommendations are based predominantly on retrospective studies that suggest improved rates of morbidity and mortality and hospital length of stay among patients treated in such a fashion. Well-designed, prospective, randomized studies confirming this tenet of therapy have not been published, although numerous prospective studies have provided indirect confirmation. The biological rationale for such a differential response (i.e., favoring combination therapy or fluoroquinolone therapy) includes the immunomodulatory effects of macrolides or more-optimal treatment of primary infection or coinfection with atypical pathogens. Well-designed, prospective, randomized trials are required to best define the effectiveness of combination therapy with a beta -lactam plus macrolide or doxycycline or with a respiratory quinolone in hospitalized patients with community-acquired pneumonia.

Levofloxacin: a review of its use in the treatment of bacterial infections in the United States

Levofloxacin (Levaquin) is a fluoroquinolone antibacterial agent with a broad spectrum of activity against Gram-positive and Gram-negative bacteria and atypical respiratory pathogens. It is active against both penicillin-susceptible and penicillin-resistant Streptococcus pneumoniae. The prevalence of S. pneumoniae resistance to levofloxacin is <1% overall in the US.A number of randomised comparative trials in the US have demonstrated the efficacy of levofloxacin in the treatment of infections of the respiratory tract, genitourinary tract, skin and skin structures. Sequential intravenous to oral levofloxacin 750mg once daily for 7-14 days was as effective in the treatment of nosocomial pneumonia as intravenous imipenem/cilastatin 500-1000mg every 6-8 hours followed by oral ciprofloxacin 750mg twice daily in one study. In patients with mild to severe community-acquired pneumonia (CAP), intravenous and/or oral levofloxacin 500mg once daily for 7-14 days achieved clinical and bacteriological response rates similar to those with comparator agents, including amoxicillin/clavulanic acid, clarithromycin, azithromycin, ceftriaxone and/or cefuroxime axetil and gatifloxacin. A recent study indicates that intravenous or oral levofloxacin 750mg once daily for 5 days is as effective as 500mg once daily for 10 days, in the treatment of mild to severe CAP. Exacerbations of chronic bronchitis and acute maxillary sinusitis respond well to treatment with oral levofloxacin 500mg once daily for 7 and 10-14 days, respectively. Oral levofloxacin was as effective as ofloxacin in uncomplicated urinary tract infections and ciprofloxacin or lomefloxacin in complicated urinary tract infections. In men with chronic bacterial prostatitis treated for 28 days, oral levofloxacin 500mg once daily achieved similar clinical and bacteriological response rates to oral ciprofloxacin 500mg twice daily. Uncomplicated skin infections responded well to oral levofloxacin 500mg once daily for 7-10 days, while in complicated skin infections intravenous and/or oral levofloxacin 750mg for 7-14 days was at least as effective as intravenous ticarcillin/clavulanic acid (+/- switch to oral amoxicillin/clavulanic acid) administered for the same duration. Levofloxacin is generally well tolerated, with the most frequently reported adverse events being nausea and diarrhoea; in comparison with some other quinolones it has a low photosensitising potential and clinically significant cardiac and hepatic adverse events are rare.

CONCLUSION

Levofloxacin is a broad-spectrum antibacterial agent with activity against a range of Gram-positive and Gram-negative bacteria and atypical organisms. It provides clinical and bacteriological efficacy in a range of infections, including those caused by both penicillin-susceptible and -resistant strains of S. pneumoniae. Levofloxacin is well tolerated, and is associated with few of the phototoxic, cardiac or hepatic adverse events seen with some other quinolones. It also has a pharmacokinetic profile that is compatible with once-daily administration and allows for sequential intravenous to oral therapy. The recent approvals in the US for use in the treatment of nosocomial pneumonia and chronic bacterial prostatitis, and the introduction of a short-course, high-dose regimen for use in CAP, further extend the role of levofloxacin in treating bacterial infections.

Drug costs and bacterial susceptibility after implementing a single-fluoroquinolone use policy at a university hospital

The University of Kentucky Hospital investigated the feasibility of choosing a sole fluoroquinolone for its formulary in an effort to reduce costs without affecting clinical outcomes. A three-step process was used to plan, implement, and monitor the selection program. Based on the range of clinical indications, safety profile, local susceptibility, cost, and dosing convenience, levofloxacin was chosen over ciprofloxacin and gatifloxacin as the sole fluoroquinolone. Since the implementation of the program in May 2001, susceptibility to levofloxacin has been maintained or increased for the most common pathogens. In addition, University Hospital has saved nearly 100,000 dollars in antibiotic acquisition costs during the first 12 months after the switch. This assessment did not take into account effects in clinical outcomes, such as clinical failures (such as readmission rates), mortality, and adverse events, or measure changes in overall medical expenditures beyond drug acquisition costs. In the future, monitoring of overall patient care and medical care costs, in addition to susceptibility patterns and drug costs, will allow for a better understanding of the long-term benefits of this switch.

Geographically dependent distribution of gyrA gene mutations at codons 83 and 87 in Salmonella Hadar, and a novel codon 81 Gly to His mutation in Salmonella Enteritidis

In all, 90 nalidixic acid-resistant clinical strains of Salmonella Hadar and Salmonella Enteritidis isolated in Norway but of predominantly foreign origin were subjected to sequencing of the gyrA, gyrB, parC and parE genes. All the isolates contained at least one mutation in gyrA codon 83 or codon 87. A highly significant correlation between mutations in gyrA codon 83 and strains originating from Southeast Asia was found in S. Hadar but not in S. Enteritidis. A novel gyrA codon 81 Gly to His mutation was discovered in one S. Enteritidis isolate. One amino-acid (aa) changing mutation was found outside the quinolone resistance-determining region (QRDR) of S. Hadar parC at codon 57, which has previously only been observed once in Salmonellae.

Selecting antibacterials for outpatient parenteral antimicrobial therapy : pharmacokinetic-pharmacodynamic considerations

Some infectious diseases require management with parenteral therapy, although the patient may not need hospitalisation. Consequently, the administration of intravenous antimicrobials in a home or infusion clinic setting has now become commonplace. Outpatient parenteral antimicrobial therapy (OPAT) is considered safe, therapeutically effective and economical. A broad range of infections can be successfully managed with OPAT, although this form of treatment is unnecessary when oral therapy can be used. Many antimicrobials can be employed for OPAT and the choice of agent(s) and regimen should be based upon sound clinical and microbiological evidence. Assessments of cost and convenience should be made subsequent to these primary treatment outcome determinants. When designing an OPAT treatment regimen, the pharmacokinetic and pharmacodynamic characteristics of the individual agents should also be considered. Pharmacokinetics (PK) is the study of the time course of absorption, distribution, metabolism and elimination of drugs (what the body does to the drug). Clinical pharmacokinetic monitoring has been used to overcome the pharmacokinetic variability of antimicrobials and enable individualised dosing regimens that attain desirable antimicrobial serum concentrations. Pharmacodynamics (PD) is the study of the relationship between the serum concentration of a drug and the clinical response observed in a patient (what the drug does to the body). By combining pharmacokinetic properties (peak [C(max)] or trough [C(min)] serum concentrations, half-life, area under the curve) and pharmacodynamic properties (susceptibility results, minimum inhibitory concentrations [MIC] or minimum bactericidal concentrations [MBC], bactericidal or bacteriostatic killing, post-antibiotic effects), unique PK/PD parameters or indices (t > MIC, C(max)/MIC, AUC(24)/MIC) can be defined. Depending on the killing characteristics of a given class of antimicrobials (concentration-dependent or time-dependent), specific PK/PD parameters may predict in vitro bacterial eradication rates and correlate with in vivo microbiologic and clinical cures. An understanding of these principles will enable the clinician to vary dosing schemes and design individualised dosing regimens to achieve optimal PK/PD parameters and potentially improve patient outcomes. This paper will review basic principles of useful PK/PD parameters for various classes of antimicrobials as they may relate to OPAT. In summary, OPAT has become an important treatment option for the management of infectious diseases in the community setting. To optimise treatment course outcomes, pharmacokinetic and pharmacodynamic properties of the individual agents should be carefully considered when designing OPAT treatment regimens.

Bacteriologic and clinical efficacy of oral gatifloxacin for the treatment of recurrent/nonresponsive acute otitis media: an open label, noncomparative, double tympanocentesis study

BACKGROUND

Gatifloxacin is an 8-methoxyfluoroquinolone with good activity against respiratory pathogens.

OBJECTIVES

To document the bacteriologic and clinical efficacy of gatifloxacin in recurrent/nonresponsive acute otitis media (AOM).

METHODS

One hundred sixty patients 6 to 48 months of age with recurrent/nonresponsive AOM received gatifloxacin suspension (10 mg/kg once daily for 10 days). Recurrent AOM was defined as > or =3 AOM episodes during the previous 6 months or > or =4 AOM episodes during the previous 12 months. Nonresponsive AOM was defined as AOM occurring < or =14 days after completing antibiotic treatment or not improving after > or =48 h of therapy. Middle ear fluid (MEF) obtained by tympanocentesis pretreatment (Day 1) and 3 to 5 days after initiation of treatment (Days 4 to 6) was cultured. Additional MEF cultures were obtained if clinical failure or recurrence of AOM occurred. Bacteriologic failure was defined by culture-positive MEF during treatment. Patients were followed until Days 22 to 28. Susceptibility was determined by broth microdilution.

RESULTS

One hundred twenty-eight (80%) patients completed treatment, and 32 discontinued the study prematurely (adverse events, 17; lost to follow-up, 10; consent withdrawal, 3; and laboratory abnormalities, 2). From 89 patients (median age, 1 year; median number of prior AOM episodes, 4; range, 0 to 12), 121 pathogens were recovered: Haemophilus influenzae, 74 (61%); Streptococcus pneumoniae, 36 (30%); Moraxella catarrhalis, 9 (7%); and Streptococcus pyogenes, 2 (2%). The 36 S. pneumoniae isolates were susceptible to gatifloxacin (MIC50 0.25 microg/ml); 26 of 36 (72%) were penicillin-nonsusceptible (15 fully resistant). All 74 H. influenzae isolates were susceptible to gatifloxacin (MIC < or = 0.03 mg/ml). Fourteen of 74 (19%) and 9 of 9 (100%) H. influenzae and M. catarrhalis isolates, respectively, produced beta-lactamase. Bacteriologic eradication was achieved for 118 of 121 (98%) pathogens: 74 of 74 H. influenzae; 34 of 36 (94%) S. pneumoniae; 9 of 9 M. catarrhalis; and 1 of 2 S. pyogenes. Clinical improvement/cure at end of treatment was seen in 103 of 114 (90%) clinically evaluable patients. Clinical recurrence of AOM after completion of therapy occurred in 31 patients. Of the 27 recurrent AOM cases in which tympanocentesis was performed, there were 16 (59%) new infections, 4 (15%) culture-negative results and only 7 (26%) true bacteriologic relapses. Adverse events were recorded in 21 of 160 (13%) patients: vomiting, 16; diarrhea, 3; maculopapular rash, 2. No articular adverse events were recorded.

CONCLUSION

Gatifloxacin is efficacious and safe for the treatment of recurrent/nonresponsive AOM.

Current Management Issues Associated with Community-Acquired Pneumonia

Community-acquired pneumonia (CAP) is a significant cause of morbidity, mortality, and increased cost. Despite numerous managementguidelines, CAP continues to existas a challenge to the learned clinician. Due to a lack of sensitive diagnostic testing, causative pathogens are often not identified, making most therapy empiric. Increasing levels of bacterial resistance to available antimicrobials worldwide has been implicated in driving up the costs of treatment and adversely effecting clinical outcomes. Pharmacists can be part of the solution by encouraging appropriate antimicrobial selection based on resistance patterns in their communities and ensuring appropriate vaccines are employed to prevent CAP.

Pharmacokinetic/Pharmacodynamic Considerations in Community-Acquired Lower Respiratory Tract Infections

To accomplish the goal of both clinical and microbiological cure in the treatment of lower respiratory tract infections, microbiological data along with pharmacokinetic and pharmacodynamic data should be used. Recent studies have determined 2important antibacterial pharmacokinetic/ pharmacodynamic parameters that differ among classes of antimicrobial agents. The 2major groups include the antibiotics that exhibit concentration-dependent killing with a postantibiotic effect and time-dependent killing with minimal to moderate postantibiotic effects. For drugs that are concentration dependent (aminoglycosides, fluoroquinolones), the area under the concentration-time curve (AUC/MIC) is the most important predictor of bacteriological eradication. Alternatively, for antibiotics that exhibit time-dependent killing (-lactams, macrolides), time above the MIC ( T >MIC) is probably the major parameter that determines efficacy. Using these parameters provides the tools needed for appropriate antibiotic dosing.

Evaluation and Prediction of Fluoroquinolone Pharmacodynamics in Bacterial Keratitis

Observational studies suggest that a pharmacodynamic index helps to predict the therapeutic outcome of respiratory and other infections. This study explored the prognostic importance of a ratio of the achievable corneal level for a fluoroquinolone to the fluoroquinolone's minimal inhibitory concentration (MIC) for corneal isolates of 391 patients with bacterial keratitis. The peak concentration and the area under the concentration curve (AUC) in the cornea were estimated from reported values achieved with topical ciprofloxacin. The inhibitory quotient (IQ) was calculated as the ratio of the estimated peak achievable corneal ciprofloxacin concentration to the ciprofloxacin MIC of keratitis isolates, and the area under the inhibitory curve (AUIC) was defined as the expected 24-hour AUC divided by the MIC. The probability of clinical improvement of ciprofloxacin-treated bacterial keratitis was 90% or more if ciprofloxacin's IQ was above 8 or the AUIC was greater than 151. A pharmacodynamic index relating corneal pharmacokinetic and susceptibility concentrations may correlate with the clinical response of bacterial keratitis to fluoroquinolone therapy.

Global patterns of susceptibility for 21 commonly utilized antimicrobial agents tested against 48,440 Enterobacteriaceae in the SENTRY Antimicrobial Surveillance Program (1997-2001)

A total of 48,440 Enterobacteriaceae isolates collected consecutively from patients hospitalized in participant SENTRY Antimicrobial Surveillance Program sites in four international regions (Asia-Pacific, Europe, Latin America, and North America) were tested by reference broth microdilution method against the most commonly used antimicrobial agents. The most active compounds could be divided in 3 groups based on their spectrum of activity. The first group included meropenem and imipenem, with 99.9% susceptibilty (S) rates for the Enterobacteriaceae. The second group includes amikacin (97.3% S) and cefepime (97.2% S); and a third active group had a rank order of susceptibility of: gatifloxacin = levofloxacin (91.7% S) > ceftazidime (91.4% S) > ceftriaxone (91.2% S) > aztreonam (91.1% S) > gentamicin (90.6% S) > piperacillin/tazobactam = ciprofloxacin (90.5% susceptibility). These latter antimicrobial agents presented susceptibility rates of approximately 90% (89.8%-91.7%). Continued resistance surveillance by various programs remain necessary to monitor the in vitro effectiveness of antimicrobial agents currently used in clinical practice.

Anaphylactoid reaction to ciprofloxacin

OBJECTIVE

To report a case of anaphylactoid reaction in an HIV-negative patient associated with the administration of intravenous ciprofloxacin.

CASE SUMMARY

A 79-year-old Armenian man developed an anaphylactoid reaction following a first-time exposure to intravenous ciprofloxacin. This reaction was characterized by severe hypotension, wheezing, tachypnea, tachycardia, and pruritus. The patient had complete recovery once ciprofloxacin treatment was terminated and supportive care was provided.

DISCUSSION

Fluoroquinolones are important therapeutic agents in the management of infectious diseases and are generally safe and well tolerated. Anaphylactoid and anaphylactic reactions have been documented as adverse effects of ciprofloxacin, ofloxacin, norfloxacin, levofloxacin, and moxifloxacin. To date, >33 cases have been reported with ciprofloxacin, of which at least 10 occurred in HIV-positive patients. In Europe, 15 cases of anaphylactoid reactions to ofloxacin have been reported and, more recently, with moxifloxacin. Since anaphylactoid reactions are potentially life threatening, the administration of fluoroquinolones to patients who have experienced a prior reaction to any of these agents should be avoided, unless tolerance has been confirmed by oral challenge tests.

CONCLUSIONS

The anaphylactoid reaction in our patient was probably induced by ciprofloxacin as validated by the Naranjo probability scale. Although anaphylactoid/anaphylactic reactions are rare adverse effects of ciprofloxacin and other fluoroquinolones, clinicians should be aware of this potentially fatal event.

Therapeutic potential of the new quinolones in the treatment of lower respiratory tract infections

The impact of respiratory infections on public health is increasing and lower respiratory tract infections are a major cause of morbidity and mortality. We are also facing a worldwide burst of antibiotic bacterial resistance. The new fluoroquinolones have an excellent spectrum covering the most important respiratory pathogens, including atypical and 'typical' pathogens. Pharmacokinetic and dynamic properties of the new fluoroquinolones have a significant impact on their clinical and bacteriological efficacy. They cause a concentration-dependent killing with a sustained postantibiotic effect. Fluoroquinolones combine exceptional efficacy with cost-effectiveness. Not surprisingly, different guidelines have inserted these agents among the drugs of choice in the empirical therapy of community-acquired pneumonia. This review discusses the more recent data on bacteriological and clinical activity and critically analyses the risks of a potential overuse of this valuable new class of drugs.

Effect of calcium carbonate on bioavailability of orally administered gemifloxacin

We investigated the effect of calcium carbonate on the oral bioavailability of gemifloxacin. Gemifloxacin was administered alone, 2 h before, simultaneously, or 2 h after calcium carbonate in 16 volunteers. Data for 320 mg of gemifloxacin alone were as follows: maximum concentration of drug in serum (C(max)),13 microg/ml; half-life, 7.33 h; and area under the concentration-time curve from 0 h to infinity (AUC( infinity )), 6.79 microg. h/ml. Only simultaneous coadministration of calcium carbonate reduced C(max) (-17%) and AUC( infinity ) (-21%) significantly.

Antimicrobial resistance in respiratory tract Streptococcus pneumoniae isolates: results of the Canadian Respiratory Organism Susceptibility Study, 1997 to 2002

A total of 6,991 unique patient isolates of Streptococcus pneumoniae were collected from October 1997 to June 2002 from 25 medical centers in 9 of the 10 Canadian provinces. Among these isolates, 20.2% were penicillin nonsusceptible, with 14.6% being penicillin intermediate (MIC, 0.12 to 1 microg/ml) and 5.6% being penicillin resistant (MIC, > or =2 microg/ml). The proportion of high-level penicillin-resistant S. pneumoniae isolates increased from 2.4 to 13.8% over the last 3 years of the study, and the proportion of multidrug-resistant S. pneumoniae isolates increased from 2.7 to 8.8% over the 5-year period. Resistant rates (intermediate and resistant) among non-beta-lactam agents were as follows: macrolides, 9.6 to 9.9%; clindamycin, 3.8%; doxycycline, 5.5%; chloramphenicol, 3.9%; and trimethoprim-sulfamethoxazole, 19.0%. Rates of resistance to non-beta-lactam agents were higher among penicillin-resistant strains than among penicillin-susceptible strains. No resistance to vancomycin or linezolid was observed; however, 0.1% intermediate resistance to quinupristin-dalfopristin was observed. The rate of macrolide resistance (intermediate and resistant) increased from 7.9 to 11.1% over the 5 years. For the fluoroquinolones, the order of activity based on the MICs at which 50% of isolates are inhibited (MIC(50)s) and the MIC(90)s was gemifloxacin > clinafloxacin > trovafloxacin > moxifloxacin > grepafloxacin > gatifloxacin > levofloxacin > ciprofloxacin. The investigational compounds ABT-773 (MIC(90), 0.008 microg/ml), ABT-492 (MIC(90), 0.015 microg/ml), GAR-936 (tigecycline; MIC(90), 0.06 microg/ml), and BMS284756 (garenoxacin; MIC(90), 0.06 micro g/ml) displayed excellent activities. Despite decreases in the rates of antibiotic consumption in Canada over the 5-year period, the rates of both high-level penicillin-resistant and multidrug-resistant S. pneumoniae isolates are increasing in Canada.

Vancomycin resistance: occurrence, mechanisms and strategies to combat it

Vancomycin has long been considered the antibiotic of last resort against serious and multi-drug-resistant infections caused by Gram-positive bacteria. However, vancomycin resistance has emerged, first in enterococci and, more recently, in Staphylococcus aureus. Here, the authors attempt to review the prevalence and the mechanisms of such resistance. Furthermore, they focus on strategies that have been developed or are under current investigation to overcome infections caused by vancomycin-resistant strains. Among these are glycopeptide derivatives with higher potency than vancomycin, small molecules that resensitise bacteria to the antibiotic and novel non-glycopeptide antibiotics. These agents are targeted to interfere with protein and/or peptidoglycan (PG) synthesis and integrity or with membrane permeability. Whilst most of these agents are still in clinical or preclinical development, some have entered the clinic and currently represent the only option for treating vancomycin-resistant enterococci (VRE).

Antimicrobial resistance in Haemophilus influenzae and Moraxella catarrhalis respiratory tract isolates: results of the Canadian Respiratory Organism Susceptibility Study, 1997 to 2002

A total of 7,566 unique patient isolates of Haemophilus influenzae and 2,314 unique patient isolates of Moraxella catarrhalis were collected between October 1997 and June 2002 from 25 medical centers in 9 of the 10 Canadian provinces. Among the 7,566 H. influenzae isolates, 22.5% produced beta-lactamase, while 92.4% of the 2,314 M. catarrhalis isolates produced beta-lactamase. The incidence of beta-lactamase-producing H. influenzae isolates decreased significantly over the 5-year study period, from 24.2% in 1997-1998 to 18.6% in 2001-2002 (P < 0.01). The incidence of beta-lactamase-producing M. catarrhalis isolates did not change over the study period. The overall rates of resistance to amoxicillin and amoxicillin-clavulanate for H. influenzae were 19.3 and 0.1%, respectively. The rank order of cephalosporin activity based on the MICs at which 90% of isolates were inhibited (MIC(90)s) was cefotaxime > cefixime > cefuroxime > cefprozil > cefaclor. On the basis of the MICs, azithromycin was more active than clarithromycin (14-OH clarithromycin was not tested); however, on the basis of the NCCLS breakpoints, resistance rates were 2.1 and 1.6%, respectively. Rates of resistance to other agents were as follows: doxycycline, 1.5%; trimethoprim-sulfamethoxazole, 14.2%; and chloramphenicol, 0.2%. All fluoroquinolones tested, including the investigational fluoroquinolones BMS284756 (garenoxacin) and ABT-492, displayed potent activities against H. influenzae, with MIC(90)s of < or = 0.03 microg/ml. The MIC(90)s of the investigational ketolides telithromycin and ABT-773 were 2 and 4 microg/ml, respectively, and the MIC(90) of the investigational glycylcycline GAR-936 (tigecycline) was 4 microg/ml. Among the M. catarrhalis isolates tested, the resistance rates derived by using the NCCLS breakpoint criteria for H. influenzae were <1% for all antibiotics tested except trimethoprim-sulfamethoxazole (1.5%). In summary, the incidence of beta-lactamase-positive H. influenzae strains in Canada is decreasing (18.6% in 2001-2002), while the incidence of beta-lactamase-positive M. catarrhalis strains has remained constant (90.0% in 2001-2002).

Fluoroquinolone-associated tendinopathy: a critical review of the literature

With the expanded use of fluoroquinolones for the treatment of community-acquired respiratory infections and reports of tendon injury linked to the use of these agents, we reviewed the literature to investigate the frequency and strength of this association. Ninety-eight case reports were available for review. The incidence of tendon injury associated with fluoroquinolone use is low in a healthy population but increases in patients who have renal dysfunction, who are undergoing hemodialysis, or who have received renal transplants. Pefloxacin and ciprofloxacin were most frequently implicated, but tendon injury was reported with most fluoroquinolones. The median duration of fluoroquinolone treatment before the onset of tendon injury was 8 days, although symptoms occurred as early as 2 hours after the first dose and as late as 6 months after treatment was stopped. Up to one-half of patients experienced tendon rupture, and almost one-third received long-term corticosteroid therapy. Tendon injury associated with fluoroquinolone use is significant, and risk factors such as renal disease or concurrent corticosteroid use must be considered when these agents are prescribed.

Chronic obstructive pulmonary disease: role of bacteria and guide to antibacterial selection in the older patient

Chronic obstructive pulmonary disease (COPD) is a common problem in the elderly. The disease is characterised by intermittent worsening of symptoms and these episodes are called acute exacerbations. The best estimate, based on several lines of evidence, is that approximately half of all exacerbations are caused by bacteria. These lines of evidence include studies of lower respiratory tract bacteriology during exacerbations, correlation of airways' inflammation with results of sputum cultures during exacerbations, analysis of immune responses to bacterial pathogens, and the observation in randomised, prospective, placebo-controlled trials that antibacterial therapy is of benefit. The most important bacterial causes of exacerbations of COPD are nontypeable Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pneumoniae and Chlamydia pneumoniae. In approaching the elderly patient with an exacerbation, it is useful to consider the severity of the exacerbation based on three cardinal symptoms: increased sputum volume, increased sputum purulence and increased dyspnoea compared with baseline. Patients experiencing moderate (two symptoms) or severe (all three symptoms) exacerbations benefit from antibacterial therapy. Consideration of underlying host factors allows for a rational choice of antibacterial agent. Patients are considered to have 'simple COPD' or 'complicated COPD' based on: (i) the severity of underlying lung disease; (ii) the frequency of exacerbations; and (iii) the presence of comorbid conditions. It is proposed that patients with simple COPD are treated with doxycycline, a newer macrolide, or an extended-spectrum oral cephalosporin; and patients with complicated COPD are treated with amoxicillin/clavulanate or a fluoroquinolone. The major goals of antibacterial therapy for exacerbations of COPD are acceleration of symptom resolution and prevention of the complications of exacerbation.

Randomized, open-label, parallel-group, multicenter study of the efficacy and tolerability of IV gatifloxacin with the option for oral stepdown gatifloxacin versus IV ceftriaxone (with or without erythromycin or clarithromycin) with the option for oral stepdown clarithromycin for treatment of patients with mild to moderate community-acquired pneumonia requiring hospitalization

BACKGROUND

Empiric therapy for community-acquired pneumonia (CAP) requires the use of antibiotics with activity against a broad spectrum of respiratory pathogens and suitable pharmacokinetic properties to simplify IV-to-oral step-down therapy switches.

OBJECTIVE

The aim of this study was to compare the efficacy and tolerability of IV gatifloxacin with the option for oral stepdown gatifloxacin with a standard regimen of IV ceftriaxone (with or without erythromycin or clarithromycin) with the option for oral stepdown clarithromycin in patients with mild to moderate CAP requiring hospitalization.

METHODS

In a randomized, open-label, parallel-group, multicenter study, adults with CAP received 7 to 14 days of treatment with either IV gatifloxacin 400 mg QD with the stepdown option or IV ceftriaxone 1 or 2 g QD (with or without erythromycin 0.5 or 1 g QID or clarithromycin 500 mg BID) with the stepdown option.

RESULTS

One hundred seventy adults with CAP were included in the study. IV gatifloxacin was stepped down to oral gatifloxacin in 90.6% (7785) of patients; IV ceftriaxone was stepped down to oral clarithromycin in 87.1% (7485) of patients. Among clinically evaluable patients (n = 153), cure rates at 1 to 3 days after treatment were 97.4% in the gatifloxacin group (7476) and 90.9% in the ceftriaxone group (7077), with a 95% CI for the difference (-3.7% to 19.1%) indicating statistical equivalence. In patients in whom pathogens were isolated from pretreatment sputum cultures, bacteriologic eradication rates were 100.0% (2929) and 90.9% (3033), respectively. Both regimens were well tolerated; treatment-related adverse events occurred in 27.1% (2385) and 21.2% (1885) of patients, respectively.

CONCLUSIONS

In the population studied, treatment with IV gatifloxacin with an option for oral stepdown gatifloxacin was as effective for achieving clinical cure as IV ceftriaxone (with or without concomitant IV erythromycin or clarithromycin) with an option for oral stepdown clarithromycin. Both regimens were well tolerated.

Novel antibacterial agents for the treatment of serious Gram-positive infections

With the continuing development of clinical drug resistance among bacteria and the advent of resistance to the recently released agents quinupristin-dalfopristin and linezolid, the need for new, effective agents to treat multi-drug-resistant Gram-positive infections remains important. This review focuses on agents presently in clinical development for the treatment of serious multidrug-resistant staphylococcal, enterococcal and pneumococcal infections, including methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci and penicillin-resistant Streptococcus pneumoniae. Agents to be discussed that affect the prokaryotic cell wall include the antimethicillin-resistant S. aureus cephalosporins BAL9141 and RWJ-54428, the glycopeptides oritavancin and dalbavancin and the lipopeptide daptomycin. Topoisomerase inhibitors include the fluoroquinolones gemifloxacin, sitafloxacin and garenoxacin. Protein synthesis inhibitors are represented by the ketolides telithromycin and cethromycin, the oxazolidinones and the glycylcycline tigecycline. Although each of these compounds has demonstrated antibacterial activity against antibiotic-resistant pathogens, their final regulatory approval will depend on an acceptable clinical safety profile.

Molecular characterization of fluoroquinolone resistant Streptococcus pneumoniae clinical isolates obtained from across Canada

There is little published data detailing fluoroquinolone resistance in clinical isolates of S. pneumoniae. The purpose of this study was to characterize the resistance mechanisms of 34 fluoroquinolone-resistant S. pneumoniae clinical isolates obtained from medical centers in 8 of 10 Canadian provinces between 1997 and 2000. The quinolone resistance determining regions of gyrA, parC, and parE from the isolates were sequenced. The isolates were evaluated for reserpine-sensitive efflux of ciprofloxacin and the new fluoroquinolones: gatifloxacin, gemifloxacin, levofloxacin and moxifloxacin. The isolates were typed using pulsed field gel electrophoresis. The majority of the isolates were genetically unrelated. Lower level fluoroquinolone resistance (ciprofloxacin MIC 4-8 microg/ml) was associated with amino acid substitutions in ParC, while higher level resistance (ciprofloxacin MIC > or = 16 microg/ml) was associated with amino acid substitutions in both ParC and GyrA. ParE substitutions were not associated with clinical resistance. Twelve of 34 (35%) isolates demonstrated reserpine-sensitive efflux of ciprofloxacin. Efflux alone conferred low level ciprofloxacin resistance in 3 isolates. Significant reserpine-sensitive efflux of the new fluoroquinolones was not observed.

Maintaining fluoroquinolone class efficacy: review of influencing factors

Previous experience with antimicrobial resistance has emphasized the importance of appropriate stewardship of these pharmacotherapeutic agents. The introduction of fluoroquinolones provided potent new drugs directed primarily against gram-negative pathogens, while the newer members of this class demonstrate more activity against gram-positive species, including Streptococcus pneumoniae. Although these agents are clinically effective against a broad range of infectious agents, emergence of resistance and associated clinical failures have prompted reexamination of their use. Appropriate use revolves around two key objectives: 1) only prescribing antimicrobial therapy when it is beneficial and 2) using the agents with optimal activity against the expected pathogens. Pharmacodynamic principles and properties can be applied to achieve the latter objective when prescribing agents belonging to the fluoroquinolone class. A focused approach emphasizing "correct-spectrum" coverage may reduce development of antimicrobial resistance and maintain class efficacy.

Safety of fluoroquinolones in paediatrics

In the last few years, there has been increasing pressure to use fluoroquinolones in paediatric patients, since these antibiotics offer the advantage of an oral treatment regimen on an out-patient basis. However, even although this class of antibiotics generally remains well-tolerated, the restriction of fluoroquinolone use in children on a compassionate basis, which derives from their potential to cause cartilage toxicity, limits the safety data in this population and suggests a cautious use. This review reports the data of the literature on the safety of fluoroquinolones in different districts, focusing on the side effects in children and drug interactions. Moreover, data available in the literature with regards to side effects in children are reported, with particular attention to their potential in arthropathy.

Evaluation and cost assessment of fluoroquinolones in community-acquired respiratory infections

Several new fluoroquinolones have been marketed since the late 1990s. Fluoroquinolones are an effective treatment for most community-acquired respiratory tract infections, including acute sinusitis, acute exacerbations of chronic bronchitis and community-acquired pneumonia. However, other antibiotics, including beta-lactams, macrolides, tetracyclines and trimethoprim-sulfamethoxazole, are also effective against these respiratory infections. From a managed care perspective, it is the subtle differences between the drugs in the eradication of bacterial pathogens, adverse effects, dose regimens, compliance issues, bacterial resistance and cost that determine the best choice for the management of pneumonia, sinusitis or exacerbations of chronic bronchitis. The potential for bacterial resistance is perhaps the only significant barrier to extensive fluoroquinolone use in community-acquired respiratory tract infections. Cost-effectiveness must be balanced with quality care, both from an individual perspective and that of the greater society.

Antibiotics in the treatment of acute exacerbations of chronic bronchitis

The benefit of antimicrobial therapy for patients with an acute exacerbation of chronic bronchitis (AECB) remains controversial for two main reasons. First, the distal airways of patients with chronic bronchitis are persistently colonised, even during clinically stable periods, with the same bacteria that have been associated with AECB. Second, bacterial infection is only one of several causes of AECB. These factors have led to conflicting analyses on the role of bacterial agents and the response to antimicrobial therapy of patients with AECB. An episode of AECB is said to be present when a patient with chronic obstructive pulmonary disease (COPD) experiences some combination of increased dyspnoea, increased sputum volume, increased sputum purulence and worsening lung function. While the average COPD patient experiences 2 - 4 episodes of AECB per year, some patients, particularly those with more severe airway obstruction, are more susceptible to these attacks than others. Bacterial agents appear to be particularly associated with AECB in patients with low lung function and those with frequent episodes accompanied by purulent sputum. Non-typeable Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis account for up to 50% of episodes of AECB. Gram-negative bacilli are more likely to occur in patients with more severe lung disease. Antibiotics have been used to ameliorate AECB, to prevent AECB and to prevent the long-term loss of lung function that characterises COPD. Numerous prevention trials have been conducted with fairly consistent results; antibiotics do not lessen the number of episodes of AECB but do reduce the number of days lost from work. Most antibiotic trials have studied the impact of treatment on episodes of AECB and results have been inconsistent, largely due to patient selection and end point definition. In patients with severe airway obstruction, especially in the presence of purulent sputum, antibiotic therapy significantly shortens the duration of symptoms and can be cost-effective. Over the past 50 years, virtually all classes of antimicrobial agents have been studied in AECB. Important considerations include penetration into respiratory secretions, spectrum of activity and antimicrobial resistance. These factors limit the usefulness of drugs such as amoxicillin, erythromycin and trimethoprim-sulfamethoxazole. Extended-spectrum oral cephalosporins, newer macrolides and doxycycline have demonstrated efficacy in clinical trials. Amoxicillin-clavulanate and flouoroquinolones should generally be reserved for patients with more severe disease. A number of investigational agents, including ketolides and newer quinolones, hold promise for treatment of AECB.

Levofloxacin

Levofloxacin is the L-form of the fluoroquinolone antibacterial agent, ofloxacin. In in vitro studies, levofloxacin demonstrated a broad range of activity against Gram-positive and -negative organisms and anaerobes. The drug is more active against Gram-positive organisms than ciprofloxacin, but less active than newer fluoroquinolones such as gatifloxacin. Its activity against Streptococcus pneumoniae is unaffected by the presence of penicillin resistance. In several randomised controlled trails, 5 to 14 days' treatment with intravenous and/or oral levofloxacin proved an effective therapy for upper and lower respiratory tract infections. In patients with mild to severe community-acquired pneumonia (CAP), intravenous and/or oral levofloxacin 500mg once or twice daily was as effective as intravenous and/or oral gatifloxacin, clarithromycin, azithromycin or amoxicillin/clavulanic acid. Overall, clinical response rates with levofloxacin ranged from 86 to 95% versus 88 to 96% with comparator agents; bacteriological response rates were 88 to 95% and 86 to 98%, respectively. Sequential (intravenous +/- oral switch) therapy with levofloxacin 750mg once daily was as effective as intravenous imipenem/cilastatin (+/- oral switch to ciprofloxacin) in patients with severe nosocomial pneumonia. Generally, oral levofloxacin 250 or 500mg once daily was at least as effective as oral cefaclor, cefuroxime axetil, clarithromycin or moxifloxacin in patients with acute exacerbations of chronic bronchitis as assessed by either clinical or bacteriological response rates. This approach also provided similar efficacy to amoxicillin/ clavulanic acid or clarithromycin in patients with acute sinusitis. Sequential therapy with levofloxacin 500mg twice daily for 7 to 14 days' was as effective as intravenous imipenem/cilastatin in patients with suspected bacteraemia. Oral levofloxacin 500mg once daily for 7 to 10 days was also an effective treatment in patients with uncomplicated skin and skin structure infections, and in those with complicated urinary tract infections. A higher dosage of sequential levofloxacin 750mg once daily proved as effective as intravenous ticarcillin/clavulanic acid (+/- oral switch to amoxicillin/clavulanic acid) in the treatment of complicated skin and skin structure infections. Pharmacoeconomic studies suggest that levofloxacin may be cost-saving in comparison to conventional therapies.

CONCLUSIONS

Levofloxacin continues to demonstrate good clinical efficacy in the treatment of a range of infections, including those in which S. pneumoniae is a potential pathogen. Importantly, it has efficacy in CAP similar to that of gatifloxacin and at least as good as that of the third generation cephalosporins. Extensive clinical data confirm the good tolerability profile of this agent without the phototoxicity, hepatic and cardiac events evident with some of the other newer fluoroquinolone agents. Levofloxacin therefore offers a unique combination of documented efficacy and tolerability, and provides an important option for the treatment of bacterial infections.