Cephalosporins

Cephalosporins are bectericidal beta-lactam antibiotics derived from fungus Acremonium They are closely related both structurally and functionally to the penicillin.
Mechanism of action: they disrupt bacterial cell wall synthesis by interfering the last step, they disrupt peptidoglycan formation in the cell wall, resulting in exposure of osmotically less stable membrane. These antibiotics are not harmful for mammalian cells because the mammalian cells do not possess cell wall.
 Organisms against which cephalosporin do not have activity are LAME
L: listeria
A: atypicals ( Mycoplasma, chlamydia)
M: MRSA (Methicillin-resistant Staphylococcus aureus)
E: Enterococci
Antibacterial Spectrum:
Cephalosporins have been classified based on their bacterial susceptibility patterns and resistance to B-lactamases  as 1st 2nd 3rd 4th and 5th generation.
1st generation are predominantly active against gram positive with succeeding generations progressively more active against gram negative strains ( often with reduce gram positive activity except 4th generation which are extended spectrum agents)
First generation: 

• Cefadroxil 
• Cefalexin 
• Cefazolin 
• Cefazedone

Second generation 

• Cefaclor
•  Cefuroxime
•  Ceftetan 
•  Cefprozil 

Third generation :

• Cefixime 
• Cefdinir
• Cefotaxime 
• Ceftrizxone 
• Cefodizine 
• Ceftazidime 

Fourth generation:

• Cedepime 
• Cefquinome 

Fifth generation:

• Ceftobiprole 
• Ceftaroline 
• Ceftolozane 

many of the cephalosporines must be administered IV or IM  because of their poor oral absorption
third generation agents achieve therapeutic level in CSF. Forth generation agents can cross the BBB so we them to treat meningitis.
Adverse Effects:
Nausea Diarrhoea rash pain and inflammation at injection site. Those allergic to penicillin may show cross sensitivity with cephalosporins, so these agents should be used with caution in individuals who are allergic to penicillin.