The safety and efficacy of clarithromycin in patients with Legionella pneumonia

In vitro activity and pharmacodynamic/pharmacokinetic parameters of clarithromycin and azithromycin: why they matter in the treatment of respiratory tract infections

Clarithromycin and azithromycin are second-generation macrolides established and widely used for treating a range of upper and lower respiratory tract infections. Extensive clinical trials data indicate that these drugs are highly effective in these applications and broadly comparable in their clinical and microbiological effectiveness. However, consideration of pharmacokinetic, metabolic, and tissue-penetration data, including the significant antibacterial activity of the metabolite 14-hydroxy-clarithromycin, plus the findings of pharmacodynamic modeling, provide evidence that the long half-life and lower potency of azithromycin predispose this agent to select for resistant isolates. Comparison of the "mutant-prevention concentrations" of clarithromycin and azithromycin, and examination of large-scale epidemiological data from Canada, also support the view that these drugs differ materially in their propensity to promote resistance among bacterial strains implicated in common respiratory infections, and that clarithromycin may offer important advantages over azithromycin that should be considered when choosing a macrolide to treat these conditions.

Cellular accumulation and pharmacodynamic evaluation of the intracellular activity of CEM-101, a novel fluoroketolide, against Staphylococcus aureus, Listeria monocytogenes, and Legionella pneumophila in human THP-1 macrophages

CEM-101 is a novel fluoroketolide with lower MICs than those of telithromycin and macrolides. Our aim was to assess the cellular accumulation and intracellular activity of CEM-101 using models developed for analyzing the pharmacokinetics and pharmacological properties of antibiotics against phagocytized bacteria. We used THP-1 macrophages and Staphylococcus aureus (ATCC 25923 [methicillin (meticillin) sensitive]), Listeria monocytogenes (strain EGD), and Legionella pneumophila (ATCC 33153). CEM-101 reached cellular-to-extracellular-concentration ratios of about 350 within 24 h (versus approximately 20, 30, and 160 for telithromycin, clarithromycin, and azithromycin, respectively). This intracellular accumulation was suppressed by incubation at a pH of < or = 6 and by monensin (proton ionophore) and was unaffected by verapamil (P-glycoprotein inhibitor; twofold accumulation increase for azithromycin) or gemfibrozil. While keeping with the general properties of the macrolide antibiotics in terms of maximal efficacy (Emax; approximately 1-log10-CFU decrease compared to the postphagocytosis inoculum after a 24-h incubation), CEM-101 showed significantly greater potency against phagocytized S. aureus than telithromycin, clarithromycin, and azithromycin (for which the 50% effective concentration [EC50] and static concentrations were about 3-, 6-, and 15-fold lower, respectively). CEM-101 was also about 50-fold and 100-fold more potent than azithromycin against phagocytized L. monocytogenes and L. pneumophila, respectively. These differences in EC50s and static concentrations between drugs were minimized when data were expressed as multiples of the MIC, demonstrating the critical role of intrinsic drug activity (MIC) in eliciting the antibacterial intracellular effects, whereas accumulation per se was unimportant. CEM-101 should show enhanced in vivo potency if used at doses similar to those of the comparators tested here.

[Routine use of extended-release clarithromycin tablets for short-course treatment of acute exacerbations of non-severe COPD]

OBJECTIVE

This study was designed to confirm, in routine clinical practice conditions, the success rates and safety of extended-release clarithromycin tablets in patients with acute exacerbation of chronic obstructive pulmonary disease (COPD), according to the usual empirical criteria in routine clinical practice.

PATIENTS AND METHODS

An open-label, pharmacoepidemiological, clinical study in community practice was performed with 180 practitioners. The bacterial origin was suspected when sputum was obviously purulent.

RESULTS

Seven hundred and nineteen adult patients with acute exacerbation of mild or moderately severe COPD were included. A favorable clinical course of the exacerbation was observed in 92.5% of cases, with resolution of frankly purulent sputum in 99% of cases, associated with good tolerance.

CONCLUSION

These results confirm the value of extended-release clarithromycin tablets as first-line treatment for presumed bacterial exacerbation of mild or moderately severe, stable COPD according to the Société de pathologie infectieuse de langue française consensus.

Antimicrobial Chemotherapy for Legionnaires Disease: Levofloxacin versus Macrolides

BACKGROUND

The community outbreak of legionnaires disease that occurred in Murcia, Spain, in July 2001--to our knowledge, the largest such outbreak ever reported--afforded an unusual opportunity to compare the clinical response of patients with Legionella pneumonia treated with levofloxacin with that of patients treated with macrolides and to determine the role of rifampicin combined with levofloxacin in treating severe legionellosis.

METHODS

An observational, prospective, nonrandomized study was conducted involving 292 patients seen at our hospital (Hospital "J. M. Morales Meseguer"; Murcia, Spain) who received a diagnosis of Legionella pneumonia during the Murcia outbreak. To compare both antibiotic regimens (macrolides vs. levofloxacin), patients were stratified by the severity of pneumonia. Duration of fever, clinical outcome, complications, side effects, and length of hospital stay were recorded. To assess the potential effects of adjuvant therapy with rifampicin, 45 case patients treated with levofloxacin plus rifampicin were evaluated and compared with 45 control pairs who were treated with levofloxacin alone.

RESULTS

With the exception of 2 patients who died, all patients were cured. There were no significant differences between treatment groups in clinical outcome for patients with mild-to-moderate pneumonia. Nevertheless, in patients with severe pneumonia, levofloxacin exerted superior activity; it was associated with fewer complications (3.4% of patients receiving levofloxacin experienced complications, compared with 27.2% of patients receiving macrolides; P=.02) and shorter mean hospital stays (5.5 vs. 11.3 days; P=.04). Addition of rifampicin to the treatment regimen for patients receiveing levofloxacin for severe pneumonia provides no additional benefit.

CONCLUSIONS

Our findings strongly suggest that monotherapy with levofloxacin is a safe and effective treatment for legionnaires disease, including in patients with severe disease. In these patients, levofloxacin appears to be more effective than clarithromycin.

Host-pathogen relationships among Escherichia coli isolates recovered from men with febrile urinary tract infection

BACKGROUND

Host-pathogen relationships in men with febrile urinary tract infection (FUTI) are poorly understood.

METHODS

Phylogenetic background, extended virulence genotypes, and serotypes were determined for 70 Escherichia coli isolates recovered from urine samples obtained from men with FUTI for comparison with available data for 70 E. coli rectal isolates recovered from uninfected men. Bacterial traits were assessed in relation to underlying host characteristics (age, compromise status, and history of urinary tract infection) and acute manifestations (bacteremia, flank pain, and serum prostate-specific antigen [PSA] level).

RESULTS

Compared with rectal isolates, FUTI isolates exhibited a significantly higher prevalence of virulence-associated phylogenetic groups, serotypes, and extraintestinal virulence genes. The latter included traditional prostatitis-associated traits (e.g., hemolysin and cytotoxic necrotizing factor), as well as unconventional traits, such as outer membrane protease T. These bacterial traits occurred largely independent of host age, urological compromise status, urinary tract infection history, and acute manifestations. However, certain traits were less prevalent in association with use of urinary tract instrumentation and significantly predicted elevated PSA levels.

CONCLUSIONS

Considerable virulence capability may be required for an E. coli strain to cause FUTI in men, regardless of whether most compromising conditions are present. Bacterial traits that promote prostatic invasion may be relevant for the pathogenesis of FUTI, even among men without classic manifestations of acute prostatitis.

Treatment of Legionnaires??? Disease

Legionnaires' disease is pneumonia, usually caused by Legionella pneumophila, which can range in severity from mild to quite severe. While it is commonly acquired in the community, it can just as easily be acquired nosocomially from water sources that have not been appropriately decontaminated. While historically initial treatment was always with erythromycin, current case series and treatment recommendations suggest that outpatients receive immediate treatment with one of the following antibacterials: azithromycin, erythromycin, clarithromycin, telithromycin, doxycycline or an extended-spectrum fluoroquinolone. If the symptoms are severe enough to warrant hospitalisation then the patient should receive treatment with parenteral azithromycin or extended-spectrum fluoroquinolones followed by step-down to oral formulations to complete the regimens. While a shorter course of 7-10 days for more severe infections may be possible for intravenous/oral azithromycin, other antibacterials should be administered for a total of 10-21 days and started as soon as possible upon presentation to optimise outcomes.

Macrolides and ketolides: azithromycin, clarithromycin, telithromycin

The advanced macrolides, azithromycin and clarithromycin, and the ketolide telithromycin are structural analogues of erythromycin. They have several distinct advantages when compared with erythromycin including enhanced spectrum of activity, more favorable pharmacokinetics and pharmacodynamics, once daily administration, and improved tolerability. This article reviews the pharmacokinetics, antimicrobial activity, clinical use, and adverse effects of these antimicrobial agents.

Monotherapy versus combination therapy for bacterial infections

The authors discuss the latest findings regarding the use of one or more antimicrobial drugs for a variety of infections. They offer suggestions for treatment based on a host of considerations, including the synergy and antagonism of specific drugs, type of infection, potential toxicities, and cost.

The newer macrolides: azithromycin and clarithromycin

Azithromycin and clarithromycin are two relatively new macrolide antimicrobial agents. Although azithromycin and clarithromycin are structural analogues of erythromycin, they offer distinct advantages in comparison. This article reviews the pharmacokinetics, antimicrobial activity, clinical use, and adverse affects of these antimicrobial agents.

The macrolides: erythromycin, clarithromycin, and azithromycin

In addition to erythromycin, macrolides now available in the United States include azithromycin and clarithromycin. These two new macrolides are more chemically stable and better tolerated than erythromycin, and they have a broader antimicrobial spectrum than erythromycin against Mycobacterium avium complex (MAC), Haemophilus influenzae, nontuberculous mycobacteria, and Chlamydia trachomatis. All three macrolides have excellent activity against the atypical respiratory pathogens (C. pneumoniae and Mycoplasma species) and the Legionella species. Azithromycin and clarithromycin have pharmacokinetics that allow shorter dosing schedules because of prolonged tissue levels. Both azithromycin and clarithromycin are active agents for MAC prophylaxis in patients with late-stage acquired immunodeficiency syndrome (AIDS), although azithromycin may be the preferable agent because of fewer drug-drug interactions. Clarithromycin is the most active MAC antimicrobial agent and should be part of any drug regimen for treating active MAC disease in patients with or without AIDS. Although both azithromycin and clarithromycin are well tolerated by children, azithromycin has the advantage of shorter treatment regimens and improved tolerance, potentially improving compliance in the treatment of respiratory tract and skin or soft tissue infections. Intravenously administered azithromycin has been approved for treatment of adults with mild to moderate community-acquired pneumonia or pelvic inflammatory diseases. An area of concern is the increasing macrolide resistance that is being reported with some of the common pathogens, particularly Streptococcus pneumoniae, group A streptococci, and H. influenzae. The emergence of macrolide resistance with these common pathogens may limit the clinical usefulness of this class of antimicrobial agents in the future.

Clarithromycin. A review of its efficacy in the treatment of respiratory tract infections in immunocompetent patients

Clarithromycin is a broad spectrum macrolide antibacterial agent active in vitro and effective in vivo against the major pathogens responsible for respiratory tract infections in immunocompetent patients. It is highly active in vitro against pathogens causing atypical pneumonia (Chlamydia pneumoniae, Mycoplasma pneumoniae and Legionella spp.) and has similar activity to other macrolides against Staphylococcus aureus. Streptococcus pyogenes, Moraxella catarrhalis and Streptococcus pneumoniae. Haemophilus influenzae is susceptible or intermediately susceptible to clarithromycin alone, but activity is enhanced when the parent drug and metabolite are combined in vitro. Absorption of clarithromycin is unaffected by food. More than half of an oral dose is systemically available as the parent drug and the active 14-hydroxy metabolite. Pharmacokinetics are nonlinear, with plasma concentrations increasing in more than proportion to the dosage. First-pass metabolism results in the rapid appearance of the active metabolite 14-hydroxy-clarithromycin in plasma. Clarithromycin and its active metabolite are found in greater concentrations in the tissues and fluids of the respiratory tract than in plasma. Dosage adjustments are required for patients with severe renal failure, but not for elderly patients or those with hepatic impairment. Drug interactions related to the cytochrome P450 system may occur with clarithromycin use. In addition to the standard immediate-release formulation for administration twice daily, a modified-release formulation of clarithromycin is now available for use once daily. In dosages of 500 to 1000 mg/day for 5 to 14 days, clarithromycin was as effective in the treatment of community-acquired upper and lower respiratory tract infections in hospital and community settings as beta-lactam agents (with or without a beta-lactamase inhibitor), cephalosporins and most other macrolides. Clarithromycin was similar in efficacy to azithromycin in comparative studies and is as effective as and better tolerated than erythromycin. Adverse events are primarily gastrointestinal in nature, but result in fewer withdrawals from therapy than are seen with erythromycin. Clarithromycin provides similar clinical and bacteriological efficacy to that seen with beta-lactam agents, cephalosporins and other macrolides. It offers a cost-saving alternative to intravenous erythromycin use in US hospitals and is available in both once-daily and twice-daily formulations. The spectrum of activity of clarithromycin against common and emerging respiratory tract pathogens may make it suitable for use in the community as empirical therapy of respiratory tract infections in both children and adults.

Choosing the right macrolide antibiotic. A guide to selection

Macrolide antibiotics have proven to be valuable alternatives to penicillins and cephalosporins for the treatment of a number of infections. Currently, a number of macrolides are available. When choosing a particular macrolide, the types of organisms causing the infection, the tolerability of the drug, convenience of dosing and possible drug interactions all must be taken into account. Erythromycin, azithromycin and clarithromycin are equally effective against most gram-positive organisms. However, clarithromycin and azithromycin have much better activity against Haemophilus influenza and Moraxella catarrhalis. Thus, these 2 drugs are better choices for the treatment of community-acquired pneumonia. However, the low serum concentrations of azithromycin may be a problem in patients with bacteraemia associated with with community-acquired pneumonia. Clarithromycin appears to be effective for the treatment and prophylaxis of Mycobacterium avium complex (MAC) in patients with AIDS, while azithromycin appears to be effective for prophylaxis. Treatment of MAC with azithromycin is currently undergoing study. Although clarithromycin is the macrolide of choice for the treatment of Helicobacter pylori, azithromycin is the preferred macrolide for the treatment of Chlamydia trachomatis infections. The major factor limiting the use of azithromycin and clarithromycin has been their cost. However, these drugs may be cost effective if compliance is improved due to better tolerability and more convenient dosing regimens.

In vitro activity of macrolides against intracellular Legionella pneumophila

The antibacterial effects of clarithromycin, azithromycin, and erythromycin were determined against five strains of Legionella pneumophila including L. pneumophila ATCC 33823 and four clinical isolates. Extracellular minimum inhibitory concentrations (MICs) and MBCs were determined by a microdilution method. Clarithromycin was the most active drug (MIC < or = 0.015-0.06), followed by azithromycin (MIC 0.03-0.12) and erythromycin (MIC 0.06-0.25). The antibacterial effect of these macrolides was then determined against L. pneumophila grown intracellularly in MRC-5 human fetal lung fibroblast cells. At two and eight times the extracellular MBC, erythromycin, azithromycin, and clarithromycin were equally effective in inhibiting growth of these five strains of intracellular L. pneumophila.

The antibiotic treatment of community-acquired, atypical, and nosocomial pneumonias

Optimal antibiotic regimens and duration of treatment are not universally agreed on for community-acquired or nosocomial pneumonias. Experience suggests that community-acquired pneumonias may be treated for less than 2 weeks with a combination of intravenous and oral antibiotics of appropriate spectrum that penetrate the lung, have a good safety profile, do not foster the development of resistance, and are cost-effective. After initial intravenous therapy, oral switch therapy may be begun as soon as the patient defervesces clinically, which is usually 3 days after admission. Switching to oral therapy does not invariably lead to earlier hospital discharge. There is no "standard of care" for pneumonias, but guidelines for empiric use have existed for decades. The least expensive beta-lactamase stable antibiotic should be used as monotherapy for the empiric treatment of community-acquired pneumonia. Because community-acquired atypical pneumonias are clinically distinct from bacterial pneumonias owing to their extrapulmonary features, clinicians should be able to differentiate atypical pneumonias from bacterial pneumonias, which permits prompt and appropriate treatment. Nosocomial pneumonias remain a difficult diagnostic challenge. Therapeutically the most important principle in treating nosocomial pneumonia is to provide for double-drug coverage against P. aeruginosa. Differentiation of respiratory tract colonization from respiratory tract invasion remains the central key issue in patients with pulmonary infiltrates acquired during hospitalization. Most patients complete their course of intravenous therapy for nosocomial pneumonia leaving little or no time for completion of their therapy by oral antibiotics. Hospital-acquired atypical pneumonias are largely limited to legionnaires' disease, which is a more difficult diagnosis than in the community-acquired setting. Clinicians taking care of patients with pneumonia should employ a simplified therapeutic approach using a single drug for community-acquired infections. The use of additional antibiotics to increase gram-negative coverage is medically unjustified and not cost-effective and is to be discouraged. The most cost-effective strategy for the treatment of community-acquired pneumonias is to switch the patient from an intravenous to an oral antibiotic as soon as the patient clinically defervesces and is able to take oral medications. Antimediator therapies have no role in the treatment of community-acquired or nosocomial pneumonias.

The role of new antibiotics for the treatment of infections in the emergency department

Treatment of infectious diseases comprises a large part of emergency medicine practice. The management of infectious diseases in the emergency department is often different than in other settings because of the types of infectious presentations and the frequent necessity of empiric treatment decisions. This paper examines the new antimicrobials and their role for the treatment of infections in the ED.

Atypical pneumonias: therapeutic possibilities

The atypical pneumonia syndrome is characterized by systemic complaints rather than respiratory symptoms. The causative pathogens include Mycoplasma, Chlamydia, Legionella and respiratory viruses (influenza, adenovirus, respiratory syncytial virus). The reported incidence of disease caused by these pathogens in community-acquired pneumonias varies from study to study. As most of these pathogens are intracellular, the antibiotics used in the treatment of atypical pneumonia are those able to penetrate into cells. Empirical antimicrobial therapy consists of macrolides (erythromycin or some of the newer agents such as roxithromycin, azithromycin or clarithromycin) or tetracyclines (e.g. doxycycline). In cases of severe legionellosis and in immunocompromised and critically-ill patients, the macrolides are sometimes given in combination with rifampicin. Promising alternatives are some of the newer fluoroquinolones (e.g. ofloxacin, pefloxacin) in the treatment of legionellosis.

Treatment of community-acquired pneumonia. A multicenter, double-blind, randomized study comparing clarithromycin with erythromycin. Canada-Sweden Clarithromycin-Pneumonia Study Group

The efficacy and safety of orally administered clarithromycin and erythromycin in the treatment of community-acquired pneumonia were assessed in a multicenter, double-blind, randomized study. Two hundred sixty-eight patients were randomized to receive either clarithromycin, 250 mg twice a day, or erythromycin stearate, 500 mg 4 times a day, for 7 to 14 days. Efficacy was evaluable in 173 patients (92 for clarithromycin, 81 for erythromycin). No statistically significant difference in clinical success rate (cure or improvement) was observed between the two groups (clarithromycin, 97 percent; erythromycin, 96 percent). Both groups had identical radiologic response (97 percent with resolution or improvement). Similarly, no statistically significant difference in bacteriologic response toward the target pathogens was observed among evaluable patients (clarithromycin, 23/26; erythromycin, 17/17; p value = 0.287). Clinical response toward Mycoplasma and Chlamydia pneumonia was comparable between the two groups (clarithromycin, 15/16; erythromycin, 10/11). However, patients receiving erythromycin had a twofold higher incidence of adverse events, mostly related to the gastrointestinal system, and were five times more likely to withdraw from therapy because of drug-related adverse events. These results show that clarithromycin is as effective as erythromycin in the outpatient treatment of community-acquired pneumonia. Furthermore, the lower incidence of adverse events associated with clarithromycin indicates that it is more acceptable to patients and, therefore, can enhance compliance.

Clarithromycin. A review of its antimicrobial activity, pharmacokinetic properties and therapeutic potential

Clarithromycin is an acid-stable orally administered macrolide antimicrobial drug, structurally related to erythromycin. It has a broad spectrum of antimicrobial activity, similar to that of erythromycin and inhibits a range of Gram-positive and Gram-negative organisms, atypical pathogens and some anaerobes. Significantly, clarithromycin demonstrates greater in vitro activity than erythromycin against certain pathogens including Bacteroides melaninogenicus, Chlamydia pneumoniae, Chlamydia trachomatis, Mycobacterium chelonae subspecies--chelonae and--abscessus, Mycobacterium leprae, Mycobacterium marinum, Mycobacterium avium complex, Legionella spp. and, when combined with its 14-hydroxy metabolite, against Haemophilus influenzae. However, bacterial strains resistant to erythromycin are also generally resistant to clarithromycin. The antimicrobial activity of clarithromycin appears to be enhanced by the formation in vivo of the microbiologically active 14-hydroxy metabolite. In combination, additive or synergistic activity against a variety of pathogens including Haemophilus influenzae, Moraxella catarrhalis, Legionella species (principally Legionella pneumophila) and various staphylococci and streptococci has been demonstrated. Clarithromycin has a superior pharmacokinetic profile to that of erythromycin, allowing the benefits of twice daily administration with the potential for increased compliance among outpatients where a more frequent regimen for erythromycin might otherwise be indicated. The clinical efficacy of clarithromycin has been confirmed in the treatment of infections of the lower and upper respiratory tracts (including those associated with atypical pathogens), skin/soft tissues, and in paediatrics. Clarithromycin was as effective as erythromycin and other appropriate drugs including beta-lactams (penicillins and cephalosporins) in some of the above infections. A most promising indication for clarithromycin appears to be in the treatment of immunocompromised patients infected with M. avium complex, M. chelonae sp. and Toxoplasma sp. Small initial trials in this setting reveal clarithromycin alone or in combination with other antimicrobials to be effective in the eradication or amelioration of these infections. Noncomparative studies have provided preliminary evidence for the effectiveness of clarithromycin in the treatment of infections of the urogenital tract, oromaxillofacial and ophthalmic areas. However, the promising in vitro and preliminary in vivo activity of clarithromycin against Mycobacterium leprae and Helicobacter pylori warrant further clinical trials to assess its efficacy in patients with these infections. Despite the improved pharmacokinetic profile and in vitro antimicrobial activity of clarithromycin over erythromycin, comparative studies of patients with community-acquired infections reveal the 2 drugs to be of equivalent efficacy. However, clarithromycin demonstrates greater tolerability, principally by inducing fewer gastrointestinal disturbances.(ABSTRACT TRUNCATED AT 400 WORDS)