Rifampicin is an antibiotic with a broad spectrum of use that differs from rifamicin SV (32.7.5), which is also used in medicine as an independent drug showing high efficacy when taken internally and having a broad antibacterial spectrum of activities.
Rifampicin exhibits an antibacterial effect by inhibiting RNA synthesis. It inhibits DNA-dependent RNA polymerase by preventing the initial development of the chain, not by removing it. Rifampicin does not bind with the RNA polymerase nucleus of mam-maliam cells, and does not have an effect on corresponding RNA synthesis. It can inhibit mitochondrial RNA synthesis; however, concentrations required for this exceed those necessary for synthesizing RNA by several hundred times.
Rifampicin is highly active with respect to Mycobacterium tuberculosis. Among atypical mycobacteria, it is active with respect to M. kansasii, M. marinum, and to most types of M. scrofulaceum and M. xenopi. The sensitivity of other mycobacteria varies. Rifampicin exhibits activity with respect to M. lepare.
Besides mycobacteria, rifampicin also exhibits activity with respect to a large number of organisms. It is highly active with respect to S. aureus, nonenterococci forms of Streptococcus and L. monocytogenes. Among Gram-negative forms, Neisseria meningi-tides, H. influenzae, and Legionella are very sensitive to rifampin. E. coli and P. mirabilis are resistant to it. Anaerobic cocci, forms of Clostridium, and Bacteroids are frequently sensitive to rifampicin.
Rifampicin is the most effective drug for treating pulmonary and non-pulmonary forms of tuberculosis, including tuberculosis meningitis. It should always be used in combination with other drugs. Synonyms of this drug are rifadin, rimactan, rifapiam, rimactazide, and others.
Polymyxines: Polymyxines are a group of related polypeptide antibiotics that are produced by sporo-forming soil bacteria Bacillus polymyxa and B. circulans, and they differ in amino acid content. Five different polymyxines have been identified—polymyxines A, B, C, D, and E, which differ in the amino acid content and are differentiated by additional letter notations and names—polymyxine B (aerosporin) and polymyxine E (colistin). It is known that in the process of development, some strains of B. polymyxa only form polymyxines A and C, and others synthesize polymyxines B and D. Polymyxine M was later isolated, a sulfomethyl derivative of polymyxine E.
Threonine and a,/-diaminobutyric acid are present within the structure of these antibiotics. The distinguishing feature of the polymyxine group is in that they contain 4-5 free /-amine groups of a,/-diaminobutyric acid, which gives them the property of a cationic detergent able to form complexes with phospholipids of cellular membranes. All polymyx-ines are similar in term of antibiotic action.
Polymyxine B is N-[3-amino-1-[[1-[[3-amino-1-[[6,9,18-tris-(2-aminoethyl)-15-benzyl-3-(1-hydroxyethyl)-12-isobutyl-2,5,8,11,14,17,20-hyptaoxo-1,4,7,10,13,16,19-heptaazacy-clotris-21-yl]-carbamoyl]-propyl]-carbamoyl]-2-hydroxypropyl]-carbamoyl]-propyl]-6-me thyloctanamide (32.7.9) [335-337].
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