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Neomycyna - Skuteczny Lek na Pryszcze?
Biosynthetic pathway [ edit ]
Neomycin was first isolated from the Streptomyces fradiae and Streptomyces albogriseus in 1949 (NBRC 12773). [18] Neomycin is a mixture of neomycin B (framycetin), and its epimer neomycin C, the latter component accounting for some 5–15% of the mixture. It is a basic compound that is most active with an alkaline reaction. [5] It is also thermostable and soluble in water (while insoluble in organic solvents). [5] Neomycin has good activity against Gram-positive and Gram-negative bacteria, but is ototoxic. Its use is thus restricted to the oral treatment of intestinal infections. [19]
Neomycin B is composed of four linked moieties: D-neosamine, 2-deoxystreptamine (2-DOS), D-ribose, and L-neosamine. [ citation needed ]
Next is the attachment of the D-ribose via ribosylation of neamine, using 5-phosphoribosyl-1-diphosphate (PRPP) as the ribosyl donor (BtrL, BtrP), [22] glycosyltransferase (potential homologues RibF, LivF, Parf) gene (Neo15). [23]
Neosamine B (L-neosamine B) is most likely biosynthesized in the same manner as the neosamine C (D-niosamine) in neamine biosynthesis, but with an additional epimerization step required to account for the presence of the epimeric neosamine B in neomycin B. [24]
Neomycin B and C are 23-carbon molecules with a four-ring structure. Three of the rings are six-membered, and one is five-membered. [25] Neomycin B and Neomycin C are stereoisomers of each other and differ by only one stereocenter one giving the R conformation and the other giving the S conformation. [26] Neomycin C can undergo enzymatic synthesis from ribostamycin. [27]
Dawkowanie neomycyny
Neomycyna występuje w formie aerozolu, tabletek oraz maści. Maść z neomycyną jest przepisywana głównie na problemy skórne oraz oczne. Tak maść, jak i aerozol nie powinny być stosowane na duże połacie skóry. Należy też unikać smarowania preparatu na uszkodzoną powierzchnię skóry, ponieważ wzrasta wówczas ryzyko przeniknięcia antybiotyku do krwi i pojawienia się niepożądanych objawów ogólnoustrojowych.
Neomycyna w tabletkach (stosowana doustnie) powinna być przyjmowana pod nadzorem lekarskim, gdyż tak aplikowany antybiotyk może wpłynąć na pogorszenie słuchu oraz funkcjonowanie nerek.
Dawkowanie ustala lekarz. Na ogół przyjmowanie antybiotyku z neomycyną przebiega w następujący sposób: 1 g co godzinę (x 4), potem 1 g co 4 godziny (przez 24 h). Neomycyna w maści zwykle podawana jest 3-5 razy dziennie.
Należy mieć świadomość, że bakteriobójcze działanie neomycyny ma miejsce jeszcze jakiś czas po wydaleniu leku z ustroju. Proces ten określa się jako efekt poantybiotykowy.
Side effects [ edit ]
In 2005–06, Neomycin was the fifth-most-prevalent allergen in patch test results (10.0%). [10] It is also a known GABA gamma-Aminobutyric acid antagonist and can be responsible for seizures and psychosis. [11] Like other aminoglycosides, neomycin has been shown to be ototoxic, causing tinnitus, hearing loss, and vestibular problems in a small number of patients. Neomycin affects the cochlea, which is found in the inner ear. [12] Hearing loss is caused by ear hair cell death, which occurs in response to treatment with neomycin. [13] Patients with existing tinnitus or sensorineural hearing loss are advised to speak with a healthcare practitioner about the risks and side effects prior to taking this medication. [ citation needed ]
Activity [ edit ]
Neomycin's antibacterial activity stems from its binding to the 30S subunit of the prokaryotic ribosome, where it inhibits prokaryotic translation of mRNA. [14]
Neomycin also exhibits a high binding affinity for phosphatidylinositol 4,5-bisphosphate (PIP2), a phospholipid component of cell membranes. [15]
Resistance [ edit ]
Neomycin resistance is conferred by either one of two kanamycin kinase genes. [16] Genes conferring neomycin-resistance are commonly included in DNA plasmids used to establish stable mammalian cell lines expressing cloned proteins in culture. Many commercially available protein expression plasmids contain a neo-resistance gene as a selectable marker. Currently, research is being performed to understand if derivatives of neomycin have the same antibiotic effects while still being effective against neomycin-resistant bacteria. [17]