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8/13/2019 Beta Galactum 1
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-Lactam antibiotic
-Lactam antibiotics(beta-lactam antibiotics) are a broad class ofantibiotics,consisting of all
antibiotic agents that contains a -lactam ring in their molecular structures. This includes
penicillin derivatives (penams), cephalosporins (cephems), monobactams, and carbapenems.Most -lactam antibiotics work by inhibitingcell wallbiosynthesis in the bacterial organism and
are the most widely used group of antibiotics. Up until 2003, when measured by sales, more than
half of all commercially available antibiotics in use were -lactam compounds. Bacteria oftendevelop resistance to -lactam antibiotics by synthesizing a-lactamase,an enzyme that attacks
the -lactam ring. To overcome this resistance, -lactam antibiotics are often given with -
lactamase inhibitors such asclavulanic acid.
Medical use
-Lactam antibiotics are indicated for the prophylaxis and treatment of bacterial infections
caused by susceptible organisms. At first, -lactam antibiotics were mainly active only againstGram-positivebacteria, yet the recent development of broad-spectrum -lactam antibiotics activeagainst variousGram-negative organisms has increased their usefulness.
Adverse effects
Adverse drug reactions
Common adverse drug reactions (ADRs) for the -lactam antibiotics include diarrhea, nausea,
rash,urticaria,superinfection (includingcandidiasis).
Infrequent ADRs include fever, vomiting, erythema, dermatitis, angioedema,pseudomembranous colitis
Pain and inflammation at the injection site is also common for parenterally administered -
lactam antibiotics.
Allergy/hypersensitivity
Immunologically mediated adverse reactions to any -lactam antibiotic may occur in up to 10%of patients receiving that agent (a small fraction of which are truly IgE-mediated allergic
reactions, see amoxicillin rash). Anaphylaxis will occur in approximately 0.01% of patients.
There is perhaps a 5%-10% cross-sensitivity between penicillin-derivatives, cephalosporins, andcarbapenems; but this figure has been challenged by various investigators.
Nevertheless, the risk of cross-reactivity is sufficient to warrant the contraindication of all -lactam antibiotics in patients with a history of severe allergic reactions (urticaria, anaphylaxis,
interstitial nephritis)to any -lactam antibiotic.
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Modes of resistance
By definition, all -lactam antibiotics have a -lactam ring in their structure. The effectiveness of
these antibiotics relies on their ability to reach the PBP intact and their ability to bind to the PBP.
Hence, there are two main modes of bacterial resistance to -lactams:
Enzymatic hydrolysis of the -lactam ring
If the bacterium produces theenzyme -lactamase or the enzymepenicillinase,the enzyme willhydrolyse the -lactam ring of the antibiotic, rendering the antibiotic ineffective. (An example
such enzyme is NDM-1, discovered in 2009.) The genes encoding these enzymes may be
inherently present on the bacterialchromosome or may be acquired viaplasmid transfer (plasmid
mediated resistance), and -lactamasegene expression may be induced by exposure to -lactams.
Clavulanic acid
Amoxicillin
The production of a -lactamase by a bacterium does not necessarily rule out all treatment
options with -lactam antibiotics. In some instances, -lactam antibiotics may be co-administered with a -lactamase inhibitor. For example, Augmentin (FGP) is made of
amoxicillin, a -lactam antibiotic, and clavulanic acid, a -lactamase inhibitor. The clavulanic
acid is designed to overwhelm all -lactamase enzymes, bind irreversibly to them, andeffectively serve as an antagonist so that the amoxicillin is not affected by the -lactamase
enzymes.
However, in all cases where infection with -lactamase-producing bacteria is suspected, thechoice of a suitable -lactam antibiotic should be carefully considered prior to treatment. In
particular, choosing appropriate -lactam antibiotic therapy is of utmost importance against
organisms with inducible -lactamase expression. If -lactamase production is inducible, thenfailure to use the most appropriate -lactam antibiotic therapy at the onset of treatment will result
in induction of -lactamase production, thereby making further efforts with other -lactam
antibiotics more difficult.
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