Linezolid : This is the first member of a new class of synthetic AMAs ‘Oxazolidinones’ which has become available for the treatment of resistant gram-positive coccal (aerobic and anaerobic) and bacillary infections.
OXAZOLIDINONE
Linezolid
This is the first
member of a new class of synthetic AMAs
‘Oxazolidinones’ which has become available for the treatment of resistant gram-positive
coccal (aerobic and anaerobic) and bacillary infections. It is active against
MRSA and some VRSA, VRE, penicillin-resistant Strep. pyogenes, Strep. viridans
and Strep. pneumoniae, M.
tuberculosis, Corynebacterium, Listeria, Clostridia and Bact. fragilis. It is primarily bacteriostatic,
but can exert cidal action against some streptococci, pneumococci and B. fragilis. Gram-negative bacteria are not
affected.
Linezolid inhibits
bacterial protein synthesis by acting at an early step and a site different
from that of other AMAs. It binds to the 23 S fraction of the 50S ribosome and
interferes with formation of the ternary N-formyl-methioninet-RNA (tRNAfMet) 70S
initiation complex. Binding of linezolid distorts the tRNA binding site
overlapping both 50S and 30S ribosomal subunits and stops protein synthesis
before it starts. As such, there is no cross resistance with any other class of
AMAs.
Linezolid is rapidly
and completely absorbed orally, partly metabolized nonenzymatically and
excreted in urine. Plasma t½ is 5 hrs. Dose modification has not been necessary
in renal insufficiency.
Linezolid has been
used for uncomplicated and complicated skin and soft tissue infections, community
and hospital acquired pneumonias, bacteraemias and other drug-resistant gram-positive
infections by oral and i.v. routes with 83–94% cure rates. However, to prevent
emergence of resistance to this valuable drug, use should be restricted to
serious hospital-acquired pneumonias, febrile neutropenia, wound infections and
others caused by multi-drugresistant gram-positive bacteria susch as VRE,
vancomycin resistant-MRSA, multi-resistant S.
pneumoniae, etc. Being bacteriostatic, it is not suitable for treatment of
enterococcal endocarditis.
Dose: 600 mg BD, oral/ i.v.; LIZOLID 600 mg tab;
LINOX 600 mg tab, 200 mg/100
ml i.v. infusion.
Side effects to
linezolid have been few; mostly mild abdominal pain and bowel upset.
Occasionally, rash, pruritus, headache, oral/ vaginal candidiasis have been
reported. Neutropenia and thrombocytopenia are infrequent and usually mild.
Because linezolid is a MAO inhibitor, interactions with adrenergic/serotonergic
drugs and excess dietary tyramine are expected. No cytochrome P450 enzyme
related interactions seem likely.
Quinupristin/Dalfopristin
It is a recently
developed combination of two
semisynthetic pristinamycin antibiotics which together exert synergistic
inhibition of bacterial protein synthesis. It is active against most gram-positive
cocci including MRSA, some VRSA and some VRE; as well as certain Neisseria, Legionella and Chlamydia pneumoniae. The combination is bactericidal against strepto and staphylococci but bacteriostatic
against E. faecium.
It is being used in Europe,
USA and some other countries for serious nosocomial MRSA, VRE and other
resistant gram positive infections.
Mupirocin
This topically used
antibiotic obtained from a species of Pseudomonas is active mainly against gram-positive
bacteria, including Strep. pyogenes
(penicillin sensitive/resistant), Staph
aureus. MRSA, etc. It inhibits bacterial protein synthesis by blocking the
production of tRNA for isoleucin. As such, no cross resistance with any other
antibiotic is seen. Though primarily bacteriostatic, high concentrations
applied topically may be bactericidal. It is indicated in furunculosis,
folliculitis, impetigo, infected insect bites and small wounds. Local itching,
irritation and redness may occur.
BACTROBAN, MUPIN, TBACT
2% oint. for topical application thrice daily.
Fusidic acid
It is a narrow
spectrum steroidal antibiotic, blocks bacterial protein synthesis and is active
against penicillinase producing Staphylococci
and few other gram-positive bacteria. It is used only topically for boils,
folliculitis, sycosis barbae and other cutaneous infections.
FUCIDINL, FUCIBACT,
FUSIDERM; 2% oint. and cream.
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