• Impair cell wall synthesis – same site and action as penicillin (similar in structure), but are more resistant to beta-lactamase.
• active against a broad spectrum
• low toxicity
• all have the nucleus of a beta-lactam ring fused to a second ring
• bind to penicillin binding proteins  disrupt cell wall synthesis and activate autolysins  damage cell wall  cell death

First generation – cephalexin, cephradine, cefactor, cefadroxil
Second generation – cefuoxime, cephamandole, cefoxitin
Third generation – cefotaxime, cefsulodin, ceftazidine, ceftazoxime, lactamoxef
Fourth generation – cefepime, cefpirome, cefditoren

• resistance develops from production of beta-lactamases (cephalosporinases) – first generation drugs are more sensitive and third generation are resistant to beta-lactamases
• generally have poor GI absorption
• Adverse reactions – nausea, vomiting, diarrhoea, skin rash

• for injection

• eg Ibilex®, Keflex®, Keftab®
• reliably active against most skin pathogens

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