Question
Enumerate Cephalosporins. Describe their mechanism of action, uses and adverse effects of third generation Cephalosporins. (4+4)
Answer
Cephalosporins, by generation
| Generation | Examples |
|---|---|
| First | Cefazolin, Cephalexin |
| Second | Cefuroxime, Cefaclor |
| Third | Ceftriaxone, Cefotaxime, Ceftazidime |
| Fourth | Cefepime |
| Fifth | Ceftaroline |
Each successive generation generally trades reduced Gram-positive activity for expanded, more potent Gram-negative coverage, and improved CNS penetration.
Third-generation cephalosporins — mechanism, uses, adverse effects Mechanism: like all beta-lactams, bind penicillin-binding proteins (transpeptidases), inhibiting peptidoglycan cross-linking and causing bactericidal cell wall failure; third-generation agents have greater stability against common bacterial beta-lactamases and substantially expanded Gram-negative spectrum compared to earlier generations, with excellent CSF penetration (ceftriaxone, cefotaxime).
Uses: bacterial meningitis (mainstay of empirical therapy, given CNS penetration and broad coverage), gonorrhoea (ceftriaxone), severe Gram-negative sepsis, typhoid fever, community-acquired pneumonia, and Pseudomonas coverage specifically with ceftazidime.
Adverse effects: hypersensitivity reactions (partial cross-reactivity with penicillin allergy), diarrhea, biliary sludging (ceftriaxone specifically, from biliary excretion), disulfiram-like reaction with alcohol (agents containing the N-methylthiotetrazole side chain), and increased C. difficile colitis risk with broad-spectrum use.