Drugs online research references
Antimicrob Agents Chemother. 1999 Oct;43(10):2468-72.
Decreased azithromycin susceptibility of Neisseria gonorrhoeae due to mtrR mutations.
Zarantonelli L, Borthagaray G, Lee EH, Shafer WM.
National Center for Gonococcal Antimicrobial Susceptibility Surveillance, Department of Microbiology, School of Chemistry, Montevideo, 11800, Uruguay.
Single-dose azithromycin therapy has recently been used in Uruguay for the treatment of uncomplicated gonococcal infections. As part of an active surveillance study to monitor the emergence of antibiotic resistance in gonococcal isolates, we examined the levels of azithromycin susceptibility in 51 consecutive isolates obtained from males with uncomplicated gonococcal urethritis. Isolates with decreased susceptibility to azithromycin (MICs, 0.25 to 0.5 microg/ml) were common, and these isolates often displayed cross-resistance to hydrophobic antimicrobial agents (erythromycin and Triton X-100). Resistance to erythromycin and Triton X-100 is frequently due to overexpression of the mtrCDE-encoded efflux pump mediated by mutations in the mtrR gene, which encodes a transcriptional repressor that modulates expression of the mtrCDE operon. Accordingly, we questioned whether clinical isolates that express decreased azithromycin susceptibility harbor mtrR mutations. Promoter mutations that would decrease the level of expression of mtrR as well as a missense mutation at codon 45 in the mtrR-coding region that would result in a radical amino acid replacement within the DNA-binding motif of MtrR were found in these strains. When these mutations were transferred into azithromycin-susceptible strain FA19 by transformation, the susceptibility of gonococci to azithromycin was decreased by nearly 10-fold. The mtrCDE-encoded efflux pump system was responsible for this property since insertional inactivation of the mtrC gene resulted in enhanced susceptibility of gonococci to azithromycin. We conclude that the mtrCDE-encoded efflux pump can recognize azithromycin and that the emergence of gonococcal strains with decreased susceptibility to azithromycin can, in part, be explained by mtrR mutations.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10508026&dopt=Abstract
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J Chromatogr. 1991 Apr 19;565(1-2):321-37.
High-performance liquid chromatographic assay with electrochemical detection for azithromycin in serum and tissues.
Shepard RM, Duthu GS, Ferraina RA, Mullins MA.
Drug Metabolism Department, Pfizer Inc., Groton, CT 06340.
High-performance liquid chromatographic methods using reversed-phase chromatography and electrochemical detection have been developed for the quantitation of azithromycin in serum and tissues of laboratory animals and humans. Serum sample preparation involved addition of internal standard, alkalinization, and solvent extraction. Tissue sample preparation involved Polytron homogenization in acetonitrile containing internal standard, evaporation of the supernatant, alkalinization of the residue, and solvent extraction. Serum samples were chromatographed on an alkylphenyl-bonded silica column eluted with pH 6.8-7.2 mobile phase with a dual-electrode coulometric detector operated in the oxidative screen mode. Serum and tissue samples were chromatographed on a gamma RP-1 alumina column with pH 11 mobile phase with a glassy carbon amperometric detector. Recovery of azithromycin was 87% from serum and 85% from tissues. Linear standard curves were prepared in serum over two concentration ranges (0.01-0.20 and 0.20-2.0 micrograms/ml) and in tissues over several concentration ranges (0.1-2, 1-10, 10-100, and 100-1000 micrograms/g). In serum and tissues, intra- and inter-assay precision ranged from 1 to 8% and 4 to 11%, respectively. The tissue assay has been applied to liver, kidney, lung, spleen, muscle, fat, brain, tonsil, lymph nodes, eye, prostate and other urological tissues, and gynecological tissues.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1651945&dopt=Abstract
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Eur J Clin Microbiol Infect Dis. 1991 Jun;10(6):519-24.
In vivo activity of the macrolide antibiotics azithromycin, roxithromycin and spiramycin against Toxoplasma gondii.
Araujo FG, Shepard RM, Remington JS.
Department of Immunology and Infectious Diseases, Research Institute, Palo Alto Medical Foundation, California 94301.
The macrolide antibiotics azithromycin, roxithromycin and spiramycin were examined in parallel for in vivo activity against Toxoplasma gondii. Azithromycin was considerably more active in protecting mice against death due to acute toxoplasmosis even when the other two antibiotics were used at twice its dose. The higher activity of azithromycin prompted a further examination of its activity against five different strains of Toxoplasma gondii, including two isolated from patients with AIDS. Although variable degrees of protection against death were noted, treatment with 200 mg/kg/day for ten days was sufficient to promote survival of 100% of mice infected with inocula as high as 1 x 10(5) tachyzoites of Toxoplasma gondii. 90% of mice inoculated with 1 x 10(5) tachyzoites of strain MO, isolated from an AIDS patient, and treated orally with 200 mg/kg/day for ten days survived the infection whereas only 40% of mice infected with the same inoculum of the SOU strain, also isolated from an AIDS patient, survived. Tissue concentrations of azithromycin were examined in treated infected and non-infected mice. In both groups of mice azithromycin attained high concentrations in liver, spleen and heart, which exceeded concurrent serum levels by 25- to 200-fold. The concentrations in the brain were almost tenfold higher than the concentrations in serum after treatment with 200 mg/kg/day for ten days. Moreover, the concentrations in brains of infected mice were approximately two-fold higher than in brains of non-infected mice.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1655433&dopt=Abstract
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