Macrolides and host defences to respiratory tract pathogens

Effect of multiple doses of clarithromycin and amoxicillin on IL-6, IFNgamma and IL-10 plasma levels in patients with community acquired pneumonia

Inflammation is crucial for the pathogenesis of both infectious and chronic obstructive pulmonary diseases. It is therefore important to modulate pulmonary inflammation in patients with these lung disorders. Macrolide antibiotics modulate inflammation in vitro and in in vivo by inhibiting the production of proinflammatory cytokines and prostaglandin E2, neutrophil chemotactic activity and elastase activity. This study evaluates the effect of clarithromycin (500 mg b.i.d. x 7 days) in comparison to amoxicillin (1 g t.i.d. x 7 days) in patients with community acquired pneumonia by testing plasma levels of IL-6, IFNgamma and IL-10 before starting therapy and at the 3rd and 7th days of therapy. Clarithromycin significantly decreased plasma levels of IL-6 and significantly increased those of IFNgamma and IL-10 at the 3rd and 7th day in comparison to basal levels. In patients treated with amoxicillin a significant decrease in IL-6 plasma levels was observed at the 7th day of therapy, probably in relation to the resolution of inflammatory symptoms. In the same patients IFNgamma plasma levels decreased during treatment while IL-10 plasma levels were unaffected.

Azithromycin versus penicillin V for treatment of acute group A streptococcal pharyngitis

OBJECTIVE

To compare a 3-day azithromycin vs. a 10-day penicillin V regimen for treatment of acute group A streptococcal (GAS) pharyngitis in children and to determine whether viral infection and/or pharyngeal GAS carriage in patients and adult contacts affect clinical and bacteriologic efficacy.

METHODS

This multicenter, randomized, comparative, open label study compared 3-day, once daily 10 mg/kg azithromycin oral suspension with a 10-day regimen of 100,000 IU/kg/day penicillin V oral suspension in three divided doses in children with acute GAS pharyngitis. Clinical and bacteriologic efficacy and tolerability of the antibiotics were evaluated. Recurrence of symptoms and infection was monitored for 6 months.

RESULTS

In total, 292 children (age range, 2 to 12 years) received at least one dose of study medication. Clinical success (cure/improvement) with either antibiotic was similar at the end of therapy (Day 14; azithromycin, 95%; penicillin V, 97%) and at Day 28 (azithromycin, 94%; penicillin V, 95%). Bacteriologic eradication was significantly less with azithromycin than with penicillin V at Day 14 (azithromycin, 38%; penicillin V, 81%; P < 0.001) and at Day 28 (azithromycin, 31%; penicillin V, 68%; P < 0.001). There was no associated increase in GAS-related sequelae. The lower incidence of bacteriologic eradication with azithromycin was not the result of possible concomitant viral infections in the patients, GAS carriage in one parent/guardian or any reduced susceptibility in pretreatment GAS isolates. Both antibiotics were equally well-tolerated.

CONCLUSIONS

Treatment with 3-day, once daily 10 mg/kg azithromycin for GAS pharyngitis is associated with similar high levels of clinical efficacy, but lower levels of bacteriologic eradication, than with 10-day 100,000 IU/kg/day penicillin V.

Azithromycin versus pivampicillin in the treatment of acute exacerbations of chronic bronchitis: a single-blind, double-dummy, multicentre study

This single-blind, double-dummy, multicentre study compared oral azithromycin, administered as tablets, 500 mg once daily for 3 days, versus oral pivampicillin, 700 mg twice daily for 10 days, in adults with acute exacerbations of chronic bronchitis (not needing parenteral antibiotic therapy, hospitalization or oxygen support). Clinical success (cure + improvement) rates were similar for both groups at the end of treatment (day 10; azithromycin, 124 of 133 [93%]; pivampicillin, 79 of 92 [86%]) and at follow-up (day 52; 98 of 126 [78%] versus 66 of 81 [81%]). The treatments produced similar levels of pathogen eradication at the end of treatment (49 of 54 [91%] versus 32 of 37 [86%]). Azithromycin-treated patients had significantly reduced chest discomfort at the end of treatment, and a trend towards improved lung function. The two groups were similar with respect to improvements in other clinical symptoms and patient well-being, and to the incidences of adverse events and treatment discontinuations. This oral azithromycin regime is an effective treatment for acute exacerbations of chronic bronchitis, similar in efficacy to the longer pivampicillin regime and may offer superior patient compliance.

Pharmacological considerations in the emergence of resistance

Resistance to macrolides in vitro is increasingly being reported. However, there has been no corresponding increase in clinical failures noted. Lack of clinical failures due to resistance is most likely the result of the high intracellular concentrations that these drugs achieve in phagocytes. In the case of clarithromycin, concentrations in both monocytes and granulocytes fluctuate between peaks of approximately 22-25 mg/l and troughs of approximately 5 mg/l during a standard dosing interval. In contrast, azithromycin attains concentrations of over 60 mg/l in granulocytes and at least 100 mg/l in monocytes. After 7 days, azithromycin concentrations of >32 mg/l are still observed. These data also imply that against pathogens with increasing minimum inhibitory concentrations (MICs), macrolides with relatively lower or less sustained intracellular concentrations will become ineffective clinically much sooner than compounds, such as azithromycin, that concentrate to a high degree and are retained in white blood cells for prolonged periods.

Macrolide antibiotics

This article is an extensive review of current information available on the macrolide antibiotics. This includes antimicrobial spectrum, pharmacology, complications and side effects, and pediatric use of these drugs. These are important antibiotics, but careful selection of patients must be made and the physician must be alert for evidence of drug-drug interactions, which are not uncommon with several members of this class.

Immunomodulating effects of antibiotics: literature review

Antibiotics can interact directly with the immune system. This is a review of the immunomodulating effects of antibiotics. The Medline database on CD-ROM was searched for the years 1987 to 1994 using the following search string: "thesaurus explode antibiotics/all AND (thesaurus explode immune-system/drug effects OR thesaurus immune-tolerance/drug effects)." Aspects of the immune system studied were aspects of phagocyte functions: phagocytosis and killing, and chemotaxis and aspects of lymphocyte functions: lymphocyte proliferation, cytokine production, antibody production, delayed hypersensitivity and natural killer-cell activity. In order to quantify and to compare immunomodulatory properties of antibiotics we calculated an "immune index," defined as: number of positive statements--number of negative statements/total number of statements. Concerning phagocytosis, positive effects were observed for cefodizime, imipenem, cefoxitin, amphotericin B and clindamycin and negative effects for erythromycin, roxithromycin, cefotaxime, tetracycline, ampicillin and gentamicin. Clindamycin, cefoxition and imipenem induce enhancement of chemotaxis, whereas cefotazime, rifampicin and teicoplanin decrease chemotaxis. Regarding lymphocyte proliferation, cefodizime has the strongest stimulating effect, whereas tetracycline has the strongest negative effect. Except for erythromycin and amphotericin B the number of statements reported is too small to be conclusive for the interpretation of effects on cytokine production. Erythromycin and amphotericin B appear to stimulate cytokine production. As to antibody production, cefodizime has the strongest positive effect, whereas josamycin, rifampicin and tetracycline have marked negative effects. For delayed hypersensitivity and the natural killer-cell activity the number of statements is too small for any single antibiotic to be conclusive. There are three markedly immuno-enhancing antibiotics (imipenem, cefodizime and clindamycin) and eight markedly immuno-depressing antibiotics (erythromycin, roxithromycin, cefotaxime, tetracycline, rifampicin, gentamicin, teicoplanin and ampicillin).

Optimum treatment of intracellular infection

The intracellular location of some micro-organisms has been early recognised as a critical point to explain failure of antibiotic therapy to eradicate such pathogens from infected hosts. Most often parasites invade 'professional' phagocytic cells, including neutrophils, monocytes and macrophages, by resisting the intracellular bactericidal phagolysosomal pathway. Alternatively, they may invade 'non-professional' phagocytic cells (cells with fewer phagocytic and bactericidal abilities) such as endothelial cells, or even cells without lysosomes such as erythrocytes. The intracellular activity of an antibiotic depends on several factors including its ability to reach the eukaryotic cell membrane, its subcellular localisation as compared to that of the parasite, the possibility that the intracellular milieu may partially inactivate its activity, and the susceptibility of the intracellular form of the parasite. In vitro and animal models have been developed to investigate antibiotic activity against intracellular pathogens. However, it should be emphasised that only data obtained from patients give reliable information to define the optimum antibiotic regimen.

The potential role of azithromycin in the treatment of prophylaxis of toxoplasmosis

Infection with Toxoplasma gondii is the most common parasitic infection worldwide with an estimated prevalence of 1-2 billion people. The risk of developing severe toxoplasmosis is higher for immunocompromised individuals and fetuses of mothers who have acquired a primo-infection. The current therapy of choice for toxoplasmosis is the synergistic combination of pyrimethamine and sulphadiazine. This therapy is highly effective but its use is complicated in immuno-compromised individuals due to adverse secondary effects. In addition, since pyrimethamine is potentially teratogenic, its use is not recommended during early pregnancy. Clindamycin, a lincosaminide, in combination with pyrimethamine has been shown to be an acceptable therapeutic alternative in patients who are unable to tolerate pyrimethamine plus sulphadiazine. In the search for new, effective compounds with less adverse or toxic effects, recent efforts have focused on the new macrolides and the azalides. Here, the results of the investigations and, in particular, the theoretical considerations for the potential use of azithromycin in the therapy of toxoplasmosis in immunocompromised individuals are reviewed.

In vitro activity of roxithromycin against the Mycobacterium tuberculosis complex

Roxithromycin has recently been shown to possess significant in vitro activity against a variety of atypical mycobacteria such as the M. avium complex, M. scrofulaceum, M. szulgai, M. malmoense, M. xenopi, M. marinum, and M. kansasii and rare pathogens like M. chelonei and M. fortuitum. In the present investigation, screening of its in vitro activity was further extended by testing it against 34 strains belonging to the M. tuberculosis complex (including M. tuberculosis, M. africanum, M. bovis, and M. bovis BCG). The MICs were determined by the radiometric BACTEC 460-TB methodology at pHs of both 6.8 and 7.4, as well as with 7H10 agar medium by the 1% proportion method. With the exception of M. bovis BCG (MIC ranges, 0.5 to 4 micrograms/ml at pH 6.8 and 0.25 to 2 micrograms/ml at pH 7.4), MICs for all of the isolates were significantly greater (MIC ranges, 32 to > 64 micrograms/ml at pH 6.8 and 16 to > 32 micrograms/ml at pH 7.4) than those reported previously for atypical mycobacteria. Roxithromycin MICs of 64 or > 64 micrograms/ml for all of the M. tuberculosis isolates screened were found by the 7H10 agar medium method. Roxithromycin, however, showed a pH-dependent bactericidal effect against M. tuberculosis because the drug was relatively more active when it was used at pH 7.4 than when it was used at pH 6.8. We conclude that roxithromycin per se is not a drug of choice for the treatment of M. tuberculosis infection or disease; however, considering its pharmacokinetics, eventual anti-tubercle bacillus activity in an in vivo system cannot yet be excluded. We suggest that the use of roxithromycin in chemoprophylactic regimens for the prevention of opportunistic infections (including M. avium complex infections) in patients with AIDS should be carefully monitored, and patients should be enrolled in such a regimen only after it has been excluded that the patient das an underlying infection of disease caused by M. tuberculosis.

Intracellular activities of roxithromycin used alone and in association with other drugs against Mycobacterium avium complex in human macrophages

Recent reports have shown that roxithromycin possesses significant activity against atypical mycobacteria, including the Mycobacterium avium complex (MAC), and that its extracellular anti-MAC activity is further enhanced in two- or three-drug combinations with ethambutol, rifampin, amikacin, ofloxacin, and clofazimine. In accordance with the above data, the anti-MAC potential of roxithromycin used alone and in combination with the above-mentioned antituberculous drugs was screened intracellularly against five clinical MAC isolates (from both human immunodeficiency virus-positive and human immunodeficiency virus-negative patients), phagocytized by human monocyte-derived macrophages. The results showed that roxithromycin used alone and within clinically achievable levels was active against all of the MAC isolates tested. Screening of two-drug combinations showed that both rifampin and clofazimine further increased the intracellular activity of roxithromycin against all five isolates by 35 to 80% (ethambutol, ofloxacin, and amikacin resulted in increased intracellular activity against one, two, and four isolates, respectively). For the three-drug combinations, the combination of roxithromycin plus ethambutol used with rifampin or clofazimine was the most uniformly active against all five MAC isolates, with activity increases of 42 to 90%, followed by roxithromycin plus ethambutol used with amikacin, which resulted in activity increases of 15 to 90%. The overall level of intracellular killing after 5 days of drug addition, in comparison with growth in untreated controls, varied from 1 to 3 log units depending on the individual MAC isolate and/or drug combination used.

Semi-synthetic derivatives of 16-membered macrolide antibiotics

The fermentation-derived 16-membered and 14-membered macrolides have been equally productive sources of semi-synthetic derivatives which have significantly extended the utility of the macrolide class as important antibiotics. New derivatives, prepared by both chemical and biochemical methods, have exhibited a variety of improved features, such as an expanded antimicrobial spectrum, increased potency, greater efficacy, better oral bioavailability, extended chemical and metabolic stability, higher and more prolonged concentrations in tissues and fluids, lower and less frequent dosing, and/or diminished side-effects [302]. However, even more improvements are both achievable and necessary if problems such as resistance to existing antibiotics continue to rise [303, 304]. Newer semi-synthetic macrolides which satisfy these important needs should be anticipated as the contributions from new fields such as genetic engineering of macrolide-producing organisms and more powerful computational chemistry are combined with the more traditional disciplines of chemical synthesis, bioconversions, and screening fermentation broths.

Semi-synthetic derivatives of erythromycin

Semi-synthetic derivatives of erythromycin have played an important role in antimicrobial chemotherapy. First generation derivatives such as 2'-esters and acid-addition salts significantly improved the chemical stability and oral bioavailability of erythromycin. A second generation of erythronolide-modified derivatives: roxithromycin, clarithromycin, azithromycin, dirithromycin and flurithromycin, have been synthesized and have exhibited significant improvements in pharmacokinetic and/or microbiological features. In addition, erythromycin itself has expanded its utility as an effective antibiotic against a variety of newly emerged pathogens. As a result of these developments, macrolide antibiotics have enjoyed a resurgence in clinical interest and use during the past half-dozen years, and semi-synthetic derivatives of erythromycin should continue to be important contributors to this macrolide renaissance. Despite these recent successes, other useful niches for macrolide antibiotics will remain unfilled. Consequently, the search for new semi-synthetic derivatives of erythromycin possessing even better antimicrobial properties should be pursued.