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Comparative antibacterial efficacies of erythromycin, clarithromycin, and azithromycin [Zithromax] were examined against Streptococcus pneumoniae and Haemophilus influenzae, with amoxicillin-clavulanate used as the active control. In vitro, the macrolides at twice their MICs and at concentrations achieved in humans were bacteriostatic or reduced the numbers of viable S. pneumoniae slowly, whereas amoxicillin-clavulanate showed a rapid antibacterial effect. Against H. influenzae, erythromycin, clarithromycin, and clarithromycin plus 14-hydroxy clarithromycin at twice their MICs produced a slow reduction in bacterial numbers, whereas azithromycin [Zithromax] was bactericidal. Azithromycin [Zithromax] at the concentrations achieved in the serum of humans was bacteriostatic, whereas erythromycin and clarithromycin were ineffective. In experimental respiratory tract infections in rats, clarithromycin (equivalent to 250 mg twice daily [b.i.d.]) and amoxicillin-clavulanate (equivalent to 500 plus 125 mg b.i.d., respectively) were highly effective against S. pneumoniae, but azithromycin [Zithromax] (equivalent to 500 and 250 mg once daily) was significantly less effective (P < 0.01). Against H. influenzae, clarithromycin treatment (equivalent to 250 or 500 mg b.i.d.) was similar to no treatment and was significantly less effective than amoxicillin-clavulanate treatment (P < 0.01). Azithromycin [Zithromax] demonstrated significant in vivo activity (P < 0.05) but was significantly less effective than amoxicillin-clavulanate (P < 0.05). Overall, amoxicillin-clavulanate was effective in vitro and in vivo. Clarithromycin and erythromycin were ineffective in vitro and in vivo against H. influenzae, and azithromycin [Zithromax] (at concentrations achieved in humans) showed unreliable activity against both pathogens. These results may have clinical implications for the utility of macrolides in the empiric therapy of respiratory tract infections.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9835514&dopt=Abstract Zithromax azithromycin




Antimicrob Agents Chemother. 2000 Jun;44(6):1754-6.
Single-oral-dose azithromycin [Zithromax] prophylaxis against experimental streptococcal or staphylococcal aortic valve endocarditis.

Tsitsika A, Pefanis A, Perdikaris GS, Donta I, Karayiannakos P, Giamarellou H.

Infectious Diseases Section, 4th Department of Medicine, Sismanoglion General Hospital, Athens University School of Medicine, Athens, Greece.

Azithromycin [Zithromax] and ampicillin protected 94 and 72% of animals challenged with Streptococcus oralis, respectively (P = 0.177), while azithromycin [Zithromax] and vancomycin protected 59 and 94% of the methicillin-resistant Staphylococcus aureus (MRSA)-challenged animals, respectively (P = 0.018). Azithromycin [Zithromax] is effective in preventing experimental streptococcal endocarditis, but against MRSA it is less effective than vancomycin.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10817749&dopt=Abstract Zithromax azithromycin




Ther Drug Monit. 1998 Dec;20(6):680-4.
Simultaneous high-performance liquid chromatography analysis of azithromycin [Zithromax] and two of its metabolites in human tears and plasma.

Raines DA, Yusuf A, Jabak MH, Ahmed WS, Karcioglu ZA, El-Yazigi A.

Department of Biological and Medical Research, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia.

This article describes a high-performance liquid chromatographic (HPLC) method for the measurement of azithromycin [Zithromax] (AZI) and two of its metabolites, 9a-N-desmethylazithromycin [Zithromax] (ADES) and N-desmethylazithromycin [Zithromax] (NDES), in human tears and plasma. The drug, metabolites, and internal standard (n-propylazithromycin [Zithromax] [IS]) were detected electrochemically after injection of the extracted sample into the HPLC system. The peak height ratio (AZI, ADES, or NDES to IS) varied linearly, with concentrations in the ranges of 0.1 mg/L to 2.0 mg/L (tears) and 0.01 mg/L to 2.0 mg/L (plasma) of AZI, ADES, and NDES; the correlation coefficient (r) was more than 0.994 mg/L for all of the compounds (n=6). The analysis of tear samples collected at different intervals within 12 hours to 144 hours after a dose of 20 mg/kg of AZI from a trachoma patient yielded concentrations ranging from 1.52 mg/L to 0.34 mg/L for AZI, 0.79 mg/L to 0.27 mg/L for ADES, and 1.99 mg/L to less than 0.20 mg/L for NDES. The concentration of AZI in plasma ranged from 0.15 mg/L to 0.01 mg/L, whereas ADES and NDES were undetectable.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9853988&dopt=Abstract Zithromax azithromycin

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We examined the effects of the macrolide antimicrobial agent azithromycin [Zithromax] and phenothiazine compounds against clinical isolates of Acanthamoeba spp. and Balamuthia mandrillaris, opportunistic pathogens of human beings and other animals. Acanthamoeba growth was inhibited in vitro at 1, 5, and 10 micrograms/ml of azithromycin, but not the macrolides, erythromycin, and clarithromycin. In experiments attempting to simulate in vivo conditions, azithromycin [Zithromax] protected monolayers of rat glioma cells from destruction by Acanthamoeba at a concentration of 0.1 microgram/ml, and delayed destruction at concentrations of 0.001 and 0.01 microgram/ml. We concluded that the minimal inhibitory concentration of azithromycin [Zithromax] was 0.1 microgram/ml. Our results, however, suggested that the drug was amebastatic but not amebicidal, since ameba growth eventually resumed after drug removal. The phenothiazines (chlorpromazine, chlorprothixene, and triflupromazine) inhibited Acanthamoeba growth by 70-90% at 5 and 10 micrograms/ml, but some of these compounds were toxic for rat glioma cells at 10 micrograms/ml. Azithromycin [Zithromax] was not very effective against B. mandrillaris in an in vitro setting, but was amebastatic in tissue culture monolayers at concentrations of 0.1 microgram/ml and higher. Balamuthia amebas showed in vitro sensitivity to phenothiazines. Ameba growth was inhibited 30-45% at 5 micrograms/ml in vitro, but completely at 5 micrograms/ml in the rat glioma model. In spite of their potential as antiamebic drugs in Balamuthia infections, toxicity of phenothiazines limits their use in clinical settings.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9864851&dopt=Abstract Zithromax azithromycin




Antimicrob Agents Chemother. 2000 Jun;44(6):1761-4.
Effect of azithromycin [Zithromax] plus rifampin versus amoxicillin alone on eradication and inflammation in the chronic course of Chlamydia pneumoniae pneumonitis in mice.

Bin XX, Wolf K, Schaffner T, Malinverni R.

Department of Clinical Research, Inselspital, University of Bern, Bern, Switzerland.

The effects of treatment with azithromycin [Zithromax] plus rifampin (A+R), amoxicillin (A), or placebo (P) on the chronic course of experimental Chlamydia pneumoniae pneumonitis in mice were assessed by culture, PCR, and immunocytochemistry as well as by degree of inflammation in lung tissue. Eradication of the pathogen was significantly more frequent and inflammation in tissue was significantly reduced after treatment with A+R compared to after treatment with A or P. Combination therapy with azithromycin [Zithromax] plus rifampin showed favorable effects in the chronic course of C. pneumoniae pneumonitis.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10817751&dopt=Abstract Zithromax azithromycin




Arch Ophthalmol. 1998 Dec;116(12):1625-8.
Ocular levels of azithromycin.

Tabbara KF, al-Kharashi SA, al-Mansouri SM, al-Omar OM, Cooper H, el-Asrar AM, Foulds G.

Department of Ophthalmology, College of Medicine, King Saud University, Riyadh, Saudi Arabia.

OBJECTIVE: To assess azithromycin [Zithromax] levels in human serum, aqueous humor, tear fluid, and conjunctival tissue specimens after administration of a single 1-g oral dose of azithromycin. METHODS: Sixty patients undergoing cataract surgery were included in this analysis. Serum, aqueous, and tear specimens were collected 3, 6, and 12 hours and 1, 2, 3, and 4 days after azithromycin [Zithromax] administration. Conjunctival tissue biopsy specimens were collected 1, 2, 3, 4, 6, 8, 10, 12, and 14 days after azithromycin [Zithromax] administration. All specimens were subjected to analysis by high-performance liquid chromatography-mass spectrometry. RESULTS: Azithromycin [Zithromax] concentration ranges during the specified sampling times were as follows: serum, 21 to 974 ng/mL; tear, 82 to 2892 ng/mL; aqueous, 10 to 69 ng/mL; and conjunctival, 0.7 to 32 micrograms/g. Levels above the 90% minimal inhibitory concentration (MIC90) for Chlamydia trachomatis were detected after 4 days in all tear samples and after 14 days in all conjunctival tissue specimens following oral azithromycin [Zithromax] administration. CONCLUSION: We demonstrated prolonged high levels of azithromycin [Zithromax] in drug-targeted ocular tissue. Prolonged high concentrations of azithromycin [Zithromax] in conjunctival tissue make this drug suitable for treatment of conjunctivitis caused by chlamydiae and other susceptible organisms.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9869792&dopt=Abstract Zithromax azithromycin




Br J Ophthalmol. 1998 Nov;82(11):1306-8.
Azithromycin [Zithromax] for ocular toxoplasmosis.

Rothova A, Bosch-Driessen LE, van Loon NH, Treffers WF.

Department of Ophthalmology, FC Donders Institute, Academic Hospital Utrecht, Netherlands.

AIMS: To investigate the efficacy of azithromycin [Zithromax] in patients with ocular toxoplasmosis. METHODS: 11 immunocompetent patients with ocular toxoplasmosis were treated with azithromycin [Zithromax] (500 mg the first day, followed by 250 mg/day for 5 weeks). Ocular and systemic examinations were performed during active retinitis episodes and all patients were followed for at least 1 year. RESULTS: The intraocular inflammation disappeared within 4 weeks in seven patients, including two cases with progressive retinitis despite previous treatment with pyrimethamine, sulphadiazine, and folinic acid. Recurrence of retinitis occurred in three patients (27%) within the first year of follow up. No systemic side effects of azithromycin [Zithromax] were encountered. CONCLUSION: These results indicate that although azithromycin [Zithromax] cannot prevent recurrent disease it may be an effective alternative for patients with ocular toxoplasmosis who cannot tolerate standard therapies.

Source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9924338&dopt=Abstract Zithromax azithromycin