Friday, 3 April 2015

Cephalosporins

CEPHALOSPORINS

These are ß-lactam antibiotics having 7-aminocephalosporanic acid nucleus, classified into 5 generations of drugs.

None of the cephalosporins are active against-
Enterococci (E.fecalis)
Listeria monocytogenes [DOC is ampicillin (not amoxycillin), sulphonamides (in case of penicillin resistance)]
Legionella
MRSA
[Mn: ELLM, as in 'elm' trees]

Most cephalosporins are excreted via kidney through tubular secretion, except Ceftriaxone & Cefoperazone (3rd generation) which are secreted in bile.

1st Generation:
✏ None of the cephalosporins are as effective as 1st gen. against gram +ve organisms (esp. cocci).
✏ Cephazolin is the DOC for Sx prophylaxis.✅
▶ Oral- cePHAlexin, cePHAradine, ceFAdroxil
▶ Parenteral- ceFAzolin, cePHAlothin
[Mn: 'Fa', 'Pha', in name/ having 'A' after 'cef-' (except- Cefaclor, 2nd gen.)]

2nd Generation:
Spectrum is extended to include H.influenzae.
Subgroup cefamycins (ceFOXitin, ceFOTetan, cefMETazole) are effective against Bacteroides fragilis.
✏ Cefuroxime attains higher CSF levels than other 2nd gen. cephalosporins.
▶ Oral- ceFAClor, cefPROzil, ceFURoxime axetil, loraCARbef
▶ Parenteral- ceFURoxime, ceFOXitin, ceFOTetan, cefMETazole
[Mn: Fur Fox Met Car Pro & Fot FACe]

3rd Generation:
✏ Spectrum is extended to include Enterobacteriacea & Pseudomonas.
✏ Penetrate BBB except ceFOperazone & ceFIxime.
✏ Ceftizoxime is most active against B.fragilis.
✏ Ceftazidime is DOC for melioidiosis by Burkholderia pseudomallei.
✏ Anti-pseudomonal are ceFTazidime & ceFOperazone (extended 3rd gen. drugs).
✏ Ceftriaxone-
DOC for gonorrhoea, salmonellosis (including typhoid), E.coli sepsis, proteus, serratia, haemophilus & empirical therapy for bacterial meningitis.
As it passes through bile, it complexes with Ca++ present in bile & causes pseudolithiasis, so is C/I in cholelithiasis.
It has the longest plasma half-life.
✏ Active metabolite of cefotaxime is desacetyl-cefotaxime.
▶ Oral- ceFIxime, ceFDinir, ceFDitoren, ceFPodoxime proxetil, ceFTibuten
▶ Parenteral- ceFOtaxime, ceFOperazone, ceFTazidime, ceFTizoxime, ceFTriaxone, mOXalactam
[Mn: 'cef-' followed by a,e,i,o,u- optional, & then either d, p or t (except- mOXalactam)]

4th Generation:
✏ Spectrum same as extended 3rd gen. drugs.
✏ Advantage is; these are extremely resistant to bacterial hydrolysis.
✏ Not effective against anaerobes.
Parenteral- cefePIme, cefPIrome
[Mn: 'Pi' in their names]

5th Generation:
✏ Approved for Rx of community acquired pneumonia & MRSA infections.
Parenteral- ceftaROLine, ceftobipROLe
[Mn: 'cef-' followed by 'Rol' in their name]

Oral/Parenteral
Mnemonic- cefotaxime, ceftriaxone, cefuroxime & anything that start with 'cef-' or 'ceph-' & have 'tin', 'thin', 'z' or 'pi' in the name are parenteral, rest all are oral.

NOTE:-
Ceftazidime + aminoglycoside - Rx of choice for pseudomonas.

Disulfiram-like reaction & hypo-prothrombinaemia is seen with those that have methyl-thio-tetra-zole (MTT) side chain group. Seen with-

2nd gen.~ ceFAMandole, ceFOTetan, cefMETazole

3rd gen.~ ceFOperazone, mOXalactam
Neutropenia is seen with - ceFTazidime.
CNS penetration is good with-

3rd gen.~ ceFOtaxime, ceFTazidime, ceFTizoxime, ceFTriaxone

4th gen.~ cefiPIme
Others have poor CNS penetration.

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