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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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