In-vitro activity of erythromycin, roxithromycin and CP 62993 against common paediatric pathogens

Nonantimicrobial Actions of Macrolides: Overview and Perspectives for Future Development

Macrolides are among the most widely prescribed broad spectrum antibacterials, particularly for respiratory infections. It is now recognized that these drugs, in particular azithromycin, also exert time-dependent immunomodulatory actions that contribute to their therapeutic benefit in both infectious and other chronic inflammatory diseases. Their increased chronic use in airway inflammation and, more recently, of azithromycin in COVID-19, however, has led to a rise in bacterial resistance. An additional crucial aspect of chronic airway inflammation, such as chronic obstructive pulmonary disease, as well as other inflammatory disorders, is the loss of epithelial barrier protection against pathogens and pollutants. In recent years, azithromycin has been shown with time to enhance the barrier properties of airway epithelial cells, an action that makes an important contribution to its therapeutic efficacy. In this article, we review the background and evidence for various immunomodulatory and time-dependent actions of macrolides on inflammatory processes and on the epithelium and highlight novel nonantibacterial macrolides that are being studied for immunomodulatory and barrier-strengthening properties to circumvent the risk of bacterial resistance that occurs with macrolide antibacterials. We also briefly review the clinical effects of macrolides in respiratory and other inflammatory diseases associated with epithelial injury and propose that the beneficial epithelial effects of nonantibacterial azithromycin derivatives in chronic inflammation, even given prophylactically, are likely to gain increasing attention in the future. SIGNIFICANCE STATEMENT: Based on its immunomodulatory properties and ability to enhance the protective role of the lung epithelium against pathogens, azithromycin has proven superior to other macrolides in treating chronic respiratory inflammation. A nonantibiotic azithromycin derivative is likely to offer prophylactic benefits against inflammation and epithelial damage of differing causes while preserving the use of macrolides as antibiotics.

Actinomycete-Derived Polyketides as a Source of Antibiotics and Lead Structures for the Development of New Antimicrobial Drugs

Actinomycetes are remarkable producers of compounds essential for human and veterinary medicine as well as for agriculture. The genomes of those microorganisms possess several sets of genes (biosynthetic gene cluster (BGC)) encoding pathways for the production of the valuable secondary metabolites. A significant proportion of the identified BGCs in actinomycetes encode pathways for the biosynthesis of polyketide compounds, nonribosomal peptides, or hybrid products resulting from the combination of both polyketide synthases (PKSs) and nonribosomal peptide synthetases (NRPSs). The potency of these molecules, in terms of bioactivity, was recognized in the 1940s, and started the "Golden Age" of antimicrobial drug discovery. Since then, several valuable polyketide drugs, such as erythromycin A, tylosin, monensin A, rifamycin, tetracyclines, amphotericin B, and many others were isolated from actinomycetes. This review covers the most relevant actinomycetes-derived polyketide drugs with antimicrobial activity, including anti-fungal agents. We provide an overview of the source of the compounds, structure of the molecules, the biosynthetic principle, bioactivity and mechanisms of action, and the current stage of development. This review emphasizes the importance of actinomycetes-derived antimicrobial polyketides and should serve as a "lexicon", not only to scientists from the Natural Products field, but also to clinicians and others interested in this topic.

The effect of carbon dioxide on susceptibility testing of azithromycin, clarithromycin and roxithromycin against clinical isolates of Streptococcus pneumoniae and Streptococcus pyogenes by broth microdilution and the Etest: Artemis Project-first-phase study

OBJECTIVE: To evaluate the effect of carbon dioxide on the susceptibility testing, using broth microdilution and the Etest (AB Biodisk, Solna, Sweden), of azithromycin, clarithromycin and roxithromycin against Streptococcus pneumoniae and Streptococcus pyogenes. METHODS: Fresh clinical isolates collected from 36 hospital laboratories in 12 countries were evaluated using the Etest in the presence of carbon dioxide. The isolates were retested under ambient conditions (absence of carbon dioxide) using broth microdilution and/or the Etest. RESULTS: Carbon dioxide falsely elevated azithromycin, clarithromycin and roxithromycin MIC90S for S. pneumoniae, determined by the Etest, approximately 12-fold. Also, the azithromycin MIC90 for S. pyogenes was increased fourfold; the effect was less marked for clarithromycin and roxithromycin. When isolates were retested in the absence of carbon dioxide, using the Etest or microdilution, susceptibilities to azithromycin were comparable to those to clarithromycin (S. pneumoniae, 93.4% versus 91.3%; S. pyogenes, 96.4% versus 95.8%). Both organisms were less susceptible to roxithromycin (S. pneumoniae, 71.3%; S. pyogenes, 85.7%). An internal standard control, consisting of 50 isolates each of S. pneumoniae, S. pyogenes and Haemophilus influenzae, confirmed that azithromycin susceptibility testing resulted in falsely elevated MICs. CONCLUSIONS: Carbon dioxide falsely elevated azithromycin MICs for S. pneumoniae and S. pyogenes, with an apparent reduction in susceptibility. When the in vitro activity of azithromycin and other macrolides against S. pneumoniae and S. pyogenes is being evaluated, awareness of the pH effect is essential.

Evaluation of the efficacy, safety and toleration of azithromycin vs. penicillin V in the treatment of acute streptococcal pharyngitis in children: results of a multicenter, open comparative study. The Swiss Tonsillopharyngitis Study Group

BACKGROUND

For many years alternatives to penicillin have been studied for the management of pediatric group A beta-hemolytic Streptococcus (GABHS) pharyngitis. As a result of its pharmacokinetic profile azithromycin is unique among these alternative antimicrobials in allowing once daily dosing and shorter duration of treatment. However, the optimum dose (e.g. 10 or 12 mg/kg/day) and duration (e.g. 3 or 5 days) of azithromycin therapy have not been defined yet.

METHODS

An open, comparative multicenter study was conducted in 343 children with clinical symptoms of GABHS pharyngitis and a positive culture to evaluate the efficacy and safety of azithromycin (10 mg/kg) once daily for 3 days compared with penicillin V three times daily for 10 days.

RESULTS

Among the evaluable patients bacteriologic eradication documented at follow-up visits was inferior with azithromycin when compared with penicillin V therapy: at Days 9 to 20 (mean, 12 days), negative cultures in 65% (99 of 152 patients) vs. 82% (128 of 126 patients) (P < 0.001); and at Days 17 to 57 (mean, 25 days), in 55% vs. 80% (P < 0.001). Overall clinical success (cure or improvement) was achieved in 93% (149 of 160 patients) of azithromycin-treated and in 89% (143 of 160 patients) of penicillin-treated patients (P > 0.50). There was no correlation between bacteriologic response and clinical outcome, as assessed shortly after completion of therapy or during 6-month follow-up. Both treatments were well-tolerated.

CONCLUSIONS

In the present study on GABHS pharyngitis in children, a once daily (10-mg/kg), 3-day oral regimen of azithromycin was as clinically effective and as safe as traditional penicillin but appeared inferior in eliminating GABHS from the throat.

Multicentre comparative study of the efficacy and safety of azithromycin compared with amoxicillin/clavulanic acid in the treatment of paediatric patients with otitis media

An open multicentre study was conducted in 484 children between the ages of 6 months and 12 years with otitis media to compare the efficacy, the safety and the tolerance of once-daily azithromycin given for three days versus thrice-daily amoxicillin/clavulanic acid (CA) given for ten days. A satisfactory response (cure plus improvement) was noted 10 to 14 days after the start of treatment in 199 of 215 (92.6%) azithromycin-treated children and in 186 of 198 (93.9%) amoxicillin/CA-treated children. The relationship between treatment and clinical response was independent of chronicity of infection and the presence or absence of a perforated eardrum. Improvement in signs and symptoms of otitis media occurred significantly more rapidly in the children treated with azithromycin. Treatment-related or possibly treatment-related adverse events were recorded in 11 of 243 (4.5%) azithromycin-treated patients and in 20 of 240 (8.3%) treated with amoxicillin/CA. No patients in the azithromycin treatment group were withdrawn from treatment, but six amoxicillin/CA patients, including two < 2 years of age, discontinued treatment prematurely because of adverse events; the difference between treatment groups was statistically significant (p = 0.0146). It is concluded that azithromycin given as an oral suspension once daily for three days is as safe and effective as amoxicillin/CA given thrice daily for ten days in the treatment of children with otitis media.

Azithromycin clinical pharmacokinetics

Azalide antibiotics, of which azithromycin is the first demonstrated, have different pharmacokinetics from other antibiotics currently used. The bioavailability of the drug is approximately 37%. Extensive and rapid distribution from serum into the intracellular compartments is followed by rapid distribution to the tissues. Tissue concentrations exceed serum concentrations by up to 100-fold following a single azithromycin 500mg dose. Concentration of the drug within phagocytes aids in its ability to combat infections. High concentrations of azithromycin are found in the tonsil, lung, prostate, lymph nodes and liver, with only small concentrations found in fat and muscle. A 500mg dose on day 1, followed by 250mg daily on days 2 to 5, has been demonstrated to maintain azithromycin concentrations at sites of infection and continues to be effective for several days after administration has ceased. The pharmacokinetics of azithromycin make it a drug with diverse therapeutic applications.

Azithromycin. A review of its antimicrobial activity, pharmacokinetic properties and clinical efficacy

Azithromycin is an acid stable orally administered macrolide antimicrobial drug, structurally related to erythromycin, with a similar spectrum of antimicrobial activity. Azithromycin is marginally less active than erythromycin in vitro against Gram-positive organisms, although this is of doubtful clinical significance as susceptibility concentrations fall within the range of achievable tissue azithromycin concentrations. In contrast, azithromycin appears to be more active than erythromycin against many Gram-negative pathogens and several other pathogens, notably Haemophilus influenzae, H. parainfluenzae, Moraxella catarrhalis, Neisseria gonorrhoeae, Urea-plasma urealyticum and Borrelia burgdorferi. Like erythromycin and other macrolides, the activity of azithromycin is unaffected by the production of beta-lactamase. However, erythromycin-resistant organisms are also resistant to azithromycin. Following oral administration, serum concentrations of azithromycin are lower than those of erythromycin, but this reflects the rapid and extensive movement of the drug from the circulation into intracellular compartments resulting in tissue concentrations exceeding those commonly seen with erythromycin. Azithromycin is subsequently slowly released, reflecting its long terminal phase elimination half-life relative to that of erythromycin. These factors allow for a single dose or single daily dose regimen in most infections, with the potential for increased compliance among outpatients where a more frequent antimicrobial regimen might traditionally be indicated. The potential disadvantage of low azithromycin serum concentrations, however, is that breakthrough bacteraemia may occur in patients who are severely ill; nevertheless, animal studies suggest that tissue concentrations of azithromycin are more important than those in serum when treating respiratory and other infections. The clinical efficacy of azithromycin has been confirmed in the treatment of infections of the lower and upper respiratory tracts (the latter including paediatric patients), skin and soft tissues (again including paediatric patients), in uncomplicated urethritis/cervicitis associated with N. gonorrhoeae, Chlamydia trachomatis or U. urealyticum and in the treatment of early Lyme disease. Azithromycin was as effective as erythromycin and other commonly used drugs including clarithromycin, beta-lactams (penicillins and cephalosporins), and quinolone and tetracycline antibiotics in some of the above infections. Some patients with acute exacerbations of chronic bronchitis due to H. influenzae may be refractory to therapy with azithromycin (as is the case with erythromycin) indicating the need for physician vigilance, although it should be noted that azithromycin is of equivalent efficacy to amoxicillin in the treatment of such patients. In the therapy of urethritis/cervicitis associated with C. trachomatis, N. gonorrhoea or U. urealyticum, a single dose azithromycin regimen offers a distinct advantage over currently available pharmacological options, while providing effective therapy.(ABSTRACT TRUNCATED AT 400 WORDS)

In vitro activity of azithromycin compared with that of erythromycin against Actinobacillus actinomycetemcomitans

The in vitro susceptibility of Actinobacillus actinomycetemcomitans to azithromycin, a new macrolide antibiotic of a new class known as azalides, was compared with that of erythromycin by the agar dilution method on Mueller-Hinton Haemophilus test medium. Eighty-two A. actinomycetemcomitans strains, 79 recent clinical isolates obtained from 40 periodontally healthy or diseased subjects, and 3 type strains were included in the study. Erythromycin showed poor in vitro activity against A. actinomycetemcomitans. Azithromycin, however, was highly effective against A. actinomycetemcomitans: all strains were inhibited at 2.0 micrograms/ml. Azithromycin exhibited the best in vitro activity against the serotype a subpopulation of A. actinomycetemcomitans: 100% of the strains were inhibited at 1.0 micrograms/ml. The lowest MICs were, however, recorded by serotype b strains. Since azithromycin has favorable pharmacokinetic properties, including excellent distribution into tissues, it could be expected to pass into gingival crevicular fluid at levels sufficient to inhibit A. actinomycetemcomitans in vivo. Therefore, it is a good candidate for future clinical trials in A. actinomycetemcomitans-associated periodontitis.

Spectrum of activity of azithromycin

In recent years, a number of newer macrolides have been developed. One such antibiotic is azithromycin, which has a 15-membered ring structure and is classed as an azalide. The limitations of erythromycin and the discovery of pathogenic bacteria such as Campylobacter, Legionella and Chlamydia species provide incentives to study the usefulness of newer antibiotics of this class. Azithromycin has good activity against staphylococci, streptococci, Moraxella catarrhalis and other rapidly growing pyogenic bacteria. The good activity of azithromycin against Haemophilus influenzae (MIC90 0.5 mg/l) is particularly important as erythromycin has only marginal activity against this organism. Azithromycin has also been shown to be more potent than the macrolides against Enterobacteriaceae. In common with erythromycin and tetracycline, the agent has good activity against Legionella, Chlamydia and Campylobacter. Opportunistic infections involving Toxoplasma gondii and Pneumocystis carinii are an increasing problem and azithromycin is particularly interesting in view of its activity against these difficult-to-treat organisms.

Concentrations of azithromycin in human tonsillar tissue

Patients scheduled to undergo tonsillectomy were administered 500 mg oral azithromycin as two 250 mg capsules given 12 h apart. Between 9 h and one week after the second dose, tonsil samples were taken during surgery and assayed for azithromycin. Mean concentrations in tonsillar tissue, 12 and 24 h after the second of the two 250 mg doses given 12 h apart, were 4.5 and 3.9 micrograms/g, respectively. Concurrent mean serum concentrations were approximately 0.03 and 0.01 micrograms/g, respectively. The mean concentration in tonsillar tissue 7.5 days after the last dose was 0.93 micrograms/g. The apparent half-life of drug in the tissue was 76 h. The ratio of mean concentration in tissue to that in serum was greater than 150-fold for all time intervals. The presence of high azithromycin concentrations in tonsillar tissue suggests that a once-daily regimen over five days or less may be effective in treating tonsillo-pharyngitis.

Clinical microbiology of azithromycin

Azithromycin contains an aza-methyl substitution in the 15-membered aglycone ring and as such it is the prototype antibiotic of the azalide class, similar in mechanism of activity to the macrolides. It demonstrates a broad spectrum of activity against many aerobic and anaerobic Gram-positive species, and also inhibits a number of important aerobic and anaerobic Gram-negative bacteria. Significantly, azithromycin shows good activity against Haemophilus influenzae, an organism against which older macrolide antibiotics have proved disappointing. It is highly effective in inhibiting clinically significant intracellular pathogens such as Chlamydia trachomatis and Legionella. Bactericidal activity is seen for certain streptococci and for H. influenzae. Closely linked with azithromycin's microbiologic activity are its novel pharmacokinetics. Azithromycin moves rapidly from blood to tissue compartments where it remains for prolonged periods. Although serum concentrations remain low, the levels attained in the tissues (often greater than 2 mg/kg) are higher than the minimum inhibitory concentration for many common pathogens, and delivery of drug to infection sites by phagocytic cells contributes to these concentrations. This penetration into eukaryotic and prokaryotic cells may be responsible for azithromycin's expanded spectrum of activity, particularly against intracellular organisms. The use of antibiotic blood levels as breakpoints for susceptibility would appear to be inappropriate in the case of azalides. Rather, levels of drug at the tissue site of infection should be considered as guides to predicting efficacy. The in vitro activity of azithromycin, together with its unique tissue pharmacodynamics, define an agent that should demonstrate utility in infections of the respiratory tract, skin and skin structures, and certain sexually transmitted diseases.

Azithromycin and amoxicillin in the treatment of acute maxillary sinusitis

Seventy-eight patients participated in this multicenter, third-party-blinded study comparing a single daily dose of azithromycin for 5 days (500 mg on day 1 followed by 250 mg/day for days 2-5) with amoxicillin (500 mg three times daily) for 10 days in the treatment of acute bacterial maxillary sinusitis. A total of 38 evaluable patients contributed to the efficacy analysis. The overall clinical response rate was 100% for both antibiotics. The clinical cure rate, as determined by the investigator, was 73.9% for azithromycin and 73.3% for amoxicillin; improvement was seen in 26.1% and 26.7% of patients, respectively. The bacteriologic cure rate in these 38 patients was 100% in both groups. Both antibiotics were well tolerated; side effects were reported by 4.9% of patients in the azithromycin group compared with 8.1% in the amoxicillin group. Most of these side effects were gastrointestinal disturbances that were reported by four of five (three amoxicillin, one azithromycin) patients experiencing side effects. All side effects were mild, and in both groups only minor abnormalities in laboratory data were detected. No patient discontinued the study because of treatment-related side effects. In this study, a 5-day course (one dose per day) of azithromycin proved to have efficacy, safety, and tolerability that was equal to a 10-day course (three doses per day) of amoxicillin in the treatment of acute bacterial sinusitis.

The effects of an antacid or cimetidine on the serum concentrations of azithromycin

The effects of an antacid and of cimetidine on the serum concentrations of azithromycin were examined in volunteers. Ten subjects were given 500 mg azithromycin alone and immediately after being given 30 mL Maalox (Rorer, Fort Washington, PA) in a crossover design. There were no statistically significant differences in Tmax or AUC0-48 after administration of azithromycin alone or with antacid, but mean values of Cmax were reduced by 24% (P = .015). Thus, although Cmax was decreased, the extent of absorption of azithromycin was not affected by coadministration with an antacid. Two groups of six volunteers were given 500 mg azithromycin on day 1. On day 8, one group was given 800 mg cimetidine 2 hours before a dose of azithromycin; the remaining group received placebo before azithromycin. There were no differences in the pharmacokinetic parameters produced by administration with cimetidine or placebo, relative to those on day 1. Thus, cimetidine administered 2 hours before a dose of azithromycin had no apparent effect on the serum concentrations of azithromycin.

Current trends and new perspectives in antibiotic therapy

During the last ten years, limitless numbers of antimicrobials were produced by the pharmaceutical industry and some have been marketed. The main objectives of new drugs are to overcome the expanding problems of resistant bacteria, to fill the gaps of spectrum of previous agents. These objectives are progressively reached by new beta-lactams, penems, fluoroquinolones; in general practice, new oral cephalosporins are becoming available. To overcome toxicity problems new concepts in antibiotic usage such as intermittent aminoglycoside regimens are suggested. Research in antibiotics, the discovery of new molecules or the re-evaluation of older drugs constitute dynamic trends in antibiotic therapy.

Quality control parameters and interpretive criteria for in vitro susceptibility tests with the macrolide azithromycin. Collaborative Antimicrobial Susceptibility Testing Group

Quality control parameters for broth microdilution and disk diffusion susceptibility tests were defined and the interpretive criteria for disk diffusion tests reviewed. For interpretation of tests with 15 micrograms azithromycin disks, the following criteria are recommended: greater than or equal to 19 mm for the susceptible category (MIC less than or equal to 2.0 micrograms/ml) and less than or equal to 15 mm for the resistant category (MIC greater than or equal to 8.0 micrograms/ml). Using these criteria, there was 97% overall agreement between broth dilution and disk diffusion tests; Haemophilus influenzae isolates were susceptible to azithromycin by both methods. The quality control strain Staphylococcus aureus ATCC 25923 gave zones of 21 to 26 mm in diameter in a six-laboratory collaborative study. In azithromycin broth microdilution tests the following MIC control limits are recommended: Escherichia coli ATCC 25922, 2.0-8.0 micrograms/ml; Staphylococcus aureus ATCC 29213, 0.25-1.0 micrograms/ml; and Enterococcus faecalis ATCC 29212, 1.0-4.0 micrograms/ml.

Roxithromycin. A review of its antibacterial activity, pharmacokinetic properties and clinical efficacy

Roxithromycin is an acid-stable orally administered antibacterial macrolide structurally related to erythromycin. It has an in vitro antibacterial profile similar to that of erythromycin, with activity against Staphylococcus aureus, S. epidermidis, Streptococcus pneumoniae, S. pyogenes, Branhamella catarrhalis, Mycoplasma pneumoniae, Legionella pneumophila, Chlamydia trachomatis, Gardnerella vaginalis, Haemophilus ducreyi, some anaerobes and other less common pathogens. Roxithromycin has a pharmacokinetic profile that is characterised by excellent enteral absorption achieving high concentrations in most tissues and body fluids. The results of clinical studies with roxithromycin have confirmed the potential for its use in a variety of infections, which was suggested by its antibacterial activity in vitro and pharmacokinetic profile. Clinical efficacy has been confirmed in the treatment of respiratory tract infections, including community-acquired and atypical pneumonias, ear, nose and throat infections, genitourinary tract infections, and skin and soft tissue infections. In a relatively small number of patients roxithromycin has generally been shown to be as effective as erythromycin and other appropriate antibacterial drugs in some of the above indications. Roxithromycin is well tolerated and has less potential than erythromycin to produce clinically significant drug interactions. Thus, roxithromycin is an orally active drug which should prove a useful alternative when selecting antibacterial therapy for indications where macrolides are appropriate.

In vitro activities of azithromycin (CP 62,993), clarithromycin (A-56268; TE-031), erythromycin, roxithromycin, and clindamycin

The in vitro activity of azithromycin (CP 62,993 or XZ-450) against Haemophilus influenzae was greater than that of three other macrolides. However, azithromycin was four- to eightfold less active than erythromycin against the gram-positive cocci and against Listeria monocytogenes. Erythromycin and azithromycin were similar in their activity against Legionella pneumophila, Neisseria gonorrhoeae, Neisseria meningitidis, and Branhamella catarrhalis.

Spectrum and mode of action of azithromycin (CP-62,993), a new 15-membered-ring macrolide with improved potency against gram-negative organisms

The macrolide antibiotic azithromycin (CP-62,993; 9-deoxo-9a-methyl-9a-aza-9a-homoerythromycin A; also designated XZ-450 [Pliva Pharmaceuticals, Zagreb, Yugoslavia]) showed a significant improvement in potency against gram-negative organisms compared with erythromycin while retaining the classic erythromycin spectrum. It was up to four times more potent than erythromycin against Haemophilus influenzae and Neisseria gonorrhoeae and twofold more potent against Branhamella catarrhalis, Campylobacter species, and Legionella species. It had activity similar to that of erythromycin against Chlamydia spp. Azithromycin was significantly more potent versus many genera of the family Enterobacteriaceae; its MIC for 90% of strains of Escherichia, Salmonella, Shigella, and Yersinia was less than or equal to 4 micrograms/ml, compared with 16 to 128 micrograms/ml for erythromycin. Azithromycin inhibited the majority of gram-positive organisms at less than or equal to 1 micrograms/ml. It displayed cross-resistance to erythromycin-resistant Staphylococcus and Streptococcus isolates. It had moderate activity against Bacteroides fragilis and was comparable to erythromycin against other anaerobic species. Azithromycin also demonstrated improved bactericidal activity in comparison with erythromycin. The mechanism of action of azithromycin was similar to that of erythromycin since azithromycin competed effectively for [14C]erythromycin ribosomebinding sites.