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Core structure of the cephalosporins
The cephalosporins (IPA: /ˌsɛfələʊˈspɔərɪn/) are a class of β-lactam antibiotics originally derived from Acremonium, which was previously known as "Cephalosporium".

Together with cephamycins they constitute a subgroup of β-lactam antibiotics called cephems.

History

Cephalosporin compounds were first isolated from cultures of Cephalosporium acremonium from a sewer in Sardinia in 1948 by Italian scientist Giuseppe Brotzu . He noticed that these cultures produced substances that were effective against Salmonella typhi, the cause of typhoid fever, which had beta-lactamase. Researchers at the Sir William Dunn School of Pathologymarker at the University of Oxfordmarker isolated cephalosporin C. The cephalosporin nucleus, 7-aminocephalosporanic acid (7-ACA), was derived from cephalosporin C and proved to be analogous to the penicillin nucleus 6-aminopenicillanic acid, but it was not sufficiently potent for clinical use. Modification of the 7-ACA side-chains resulted in the development of useful antibiotic agents, and the first agent cephalothin (cefalotin) was launched by Eli Lilly in 1964.

Mode of action

Cephalosporins are bactericidal and have the same mode of action as other beta-lactam antibiotics (such as penicillins) but are less susceptible to penicillinases. Cephalosporins disrupt the synthesis of the peptidoglycan layer of bacterial cell walls. The peptidoglycan layer is important for cell wall structural integrity. The final transpeptidation step in the synthesis of the peptidoglycan is facilitated by transpeptidases known as penicillin binding proteins (PBPs). PBPs bind to the D-Ala-D-Ala at the end of muropeptides (peptidoglycan precursors) to crosslink the peptidoglycan. Beta-lactam antibiotics mimic this site and competitively inhibit PBP crosslinking of peptidoglycan.

Clinical use

Indications

Cephalosporins are indicated for the prophylaxis and treatment of infections caused by bacteria susceptible to this particular form of antibiotic. First-generation cephalosporins are predominantly active against Gram-positive bacteria, and successive generations have increased activity against Gram-negative bacteria (albeit often with reduced activity against Gram-positive organisms).

Adverse effects

Common adverse drug reactions (ADRs) (≥1% of patients) associated with the cephalosporin therapy include: diarrhea, nausea, rash, electrolyte disturbances, and/or pain and inflammation at injection site. Infrequent ADRs (0.1–1% of patients) include: vomiting, headache, dizziness, oral and vaginal candidiasis, pseudomembranous colitis, superinfection, eosinophilia, and/or fever.

The commonly quoted figure of 10% of patients with allergic hypersensitivity to penicillins and/or carbapenems also having cross-reactivity with cephalosporins originated from a 1975 study looking at the original cephalosporins, and subsequent "safety first" policy meant this was widely quoted and assumed to apply to all members of the group. Hence it was commonly stated that they are contraindicated in patients with a history of severe, immediate allergic reactions (urticaria, anaphylaxis, interstitial nephritis, etc) to penicillins, carbapenems or cephalosporins. This however should be viewed in the light of recent epidemiological work suggesting that for many 2nd generation (or later) cephalosporins that the cross-reactivity rate with penicillin is much lower, having no significantly increased risk of reactivity in the studies examined. The British National Formulary previously issued blanket warnings of 10% cross reactivity; but since the September 2008 edition suggests in the absence of suitable alternatives that oral cefixime or cefuroxime and injectable cefotaxime, ceftazidine and ceftriaxone can be used with caution, but to avoid cefaclor, cefadrocil, cefalexin and cefradine.

Several cephalosporins are associated with hypoprothrombinemia and a disulfiram-like reaction with ethanol. These include latamoxef, cefmenoxime, moxalactam, cefoperazone, cefamandole, cefmetazole, and cefotetan. This is thought to be due to the N-methylthiotetrazole (NMTT) side chain of these cephalosporins, which blocks the enzyme vitamin K epoxide reductase (likely causing hypothrombinemia) and aldehyde dehydrogenase (causing alcohol intolerance).

Classification

The cephalosporin nucleus can be modified to gain different properties. Cephalosporins are sometimes grouped into "generations" by their antimicrobial properties. The first cephalosporins were designated first generation, whereas later, more extended spectrum cephalosporins were classified as second-generation cephalosporins. Each newer generation of cephalosporins has significantly greater Gram-negative antimicrobial properties than the preceding generation, in most cases with decreased activity against Gram-positive organisms. Fourth-generation cephalosporins, however, have true broad spectrum activity.

The classification of cephalosporins into "generations" is commonly practised, although the exact categorisation of cephalosporins is often imprecise. For example, the fourth generation of cephalosporins is not yet recognized in Japan. In Japan, cefaclor is classed as a first-generation cephalosporin, even though in the United States it is a 2nd generation; and cefbuperazone, cefminox, and cefotetan are classed as second-generation cephalosporins. Cefmetazole and cefoxitin are classed as third-generation cephems. Flomoxef, latamoxef are in a new class called oxacephems.

Most first-generation cephalosporins were originally spelled "ceph-" in English-speaking countries. This continues to be the preferred spelling in the US and Australia, while European countries have adopted International Nonproprietary Names, which are usually spelled "cef-". Newer first-generation cephalosporins and all cephalosporins of later generations are spelled "cef-".

Some state that although cephalosporins can be divided into five or even six generations, the usefulness of this organization system is of limited clinical relevance.

First generation

Structure of the classical cephalosporins
Although first-generation cephalosporins are moderate spectrum agents, with a spectrum of activity of bacteria that includes penicillinase-producing, methicillin-susceptible staphylococci and streptococci, they are not the drugs of choice for such infections. They also have activity against some Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis, but have no activity against Bacteroides fragilis, enterococci, methicillin-resistant staphylococci, Pseudomonas, Acinetobacter, Enterobacter, indole-positive Proteus, or Serratia.



Second generation

The second-generation cephalosporins have a greater Gram-negativespectrum while retaining some activity against Gram-positive cocci. They are also more resistant to beta-lactamase.



Second generation cephalosporins with antianaerobe activity

The following cephems are also sometimes grouped with second-generation cephalosporins:

Third generation

Third-generation cephalosporins have a broad spectrum of activity and further increased activity against Gram-negative organisms. Some members of this group (in particular, those available in an oral formulation, and those with anti-pseudomonal activity) have decreased activity against Gram-positive organisms. They may be particularly useful in treating hospital-acquired infection, although increasing levels of extended-spectrum beta-lactamases are reducing the clinical utility of this class of antibiotics. They are also able to penetrate the CNS, making them useful against meningitis caused bypneumococci, meningococci, H. influenzae, and susceptible E. coli, Klebsiella, and penicillin-resistant N. gonorrhoeae. Since 2007, third-generation cephalosporins (ceftriaxone or cefixime) have been the only recommended treatment for gonorrhea in the United States.



Third-generation cephalosporins with antipseudomonal activity

The following cephems are also sometimes grouped with third-generation cephalosporins:

Fourth generation

Fourth-generation cephalosporins are extended-spectrum agents with similar activity against Gram-positive organisms as first-generation cephalosporins. They also have a greater resistance to beta-lactamases than the third-generation cephalosporins. Many can cross the blood-brain barrier and are effective in meningitis. They are also used against Pseudomonas aeruginosa.



The following cephems are also sometimes grouped with third-generation cephalosporins:

Fifth generation

Ceftobiprole has been described as "fifth generation", though acceptance for this terminology is not universal.

Ceftobiprole (and the soluble prodrug medocaril) are on the FDA fast-track. Ceftobiprole has powerful antipseudomonal characteristics and appears to be less susceptible to development of resistance.

Yet to be classified

These cephems have progressed far enough to be named, but have not been assigned to a particular generation.



See also



References

  1. Podolsky, M. Lawrence (1998) Cures Out of Chaos: How Unexpected Discoveries Led to Breakthroughs in Medicine and Health, Harwood Academic Publishers
  2. Rossi S, editor. Australian Medicines Handbook 2006. Adelaide: Australian Medicines Handbook; 2006.


Further reading

  • CXA-101 under development at Calixa Therapeutics, described as "a novel cephalosporin antibiotic".



External links




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