Classification of Cephalosporins, Monobactams, and Carbapenems

Classification of Cephalosporins, Monobactams, and Carbapenems

1. Classification of Cephalosporins

By Generation:

1st Gen – Cephalexin, Cefadroxil (Gram +ve > Gram –ve)
2nd Gen – Cefuroxime, Cefaclor (↑ Gram –ve coverage)
3rd Gen – Cefixime, Cefpodoxime proxetil, Cefotaxime, Ceftriaxone (Broad spectrum, CNS penetration)
4th Gen – Cefepime (↑ Gram –ve, Pseudomonas coverage)
5th Gen – Ceftaroline (MRSA coverage) – (Not in your given list but for context)

2. Mechanism of Action (Common for β-lactams)

Inhibit bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs) → block peptidoglycan cross-linking → cell lysis (bactericidal).

3. Therapeutic Uses

1st Gen – Skin/soft tissue infections, surgical prophylaxis.
2nd Gen – Respiratory tract infections, otitis media, sinusitis.
3rd Gen – Meningitis, gonorrhea, typhoid fever, severe Gram –ve infections.
4th Gen – Febrile neutropenia, hospital-acquired infections.

4. Adverse Effects

Hypersensitivity (rash → anaphylaxis)
GI upset, diarrhea
Superinfection (e.g., C. difficile)
Nephrotoxicity (rare, ↑ risk with aminoglycosides)
Disulfiram-like reaction (esp. cefotetan, cefoperazone)

5. Dosage (Examples)

Cephalexin – 250–500 mg q6h PO
Ceftriaxone – 1–2 g/day IV/IM
Cefepime – 1–2 g q8–12h IV
(Dose adjustment in renal impairment)

6. Contraindications

Severe hypersensitivity to β-lactams
Use with caution in penicillin allergy
Dose adjust in renal impairment

7. Drug Interactions

Aminoglycosides – ↑ nephrotoxicity risk
Warfarin – ↑ INR (alters gut flora → ↓ vitamin K)
Loop diuretics – ↑ nephrotoxicity risk

Cephalosporin + β-Lactamase Inhibitors

Examples: Cefoperazone–Sulbactam, Ceftazidime–Avibactam
Advantage: Overcome β-lactamase–mediated resistance.
Uses: Multidrug-resistant Gram –ve infections, hospital-acquired pneumonia, complicated UTIs.

Monobactams (Aztreonam)

MOA: Same as β-lactams; binds PBP-3 → inhibits cell wall synthesis (specific for aerobic Gram –ve).
Uses: Serious Gram –ve infections (esp. Pseudomonas), safe in penicillin allergy.
Adverse: Rash, GI upset, ↑ liver enzymes.
Dosage: 1–2 g IV/IM q8–12h.
Contraindication: Hypersensitivity to aztreonam.
Interactions: Minimal; safe with aminoglycosides.

Carbapenems

1. Imipenem–Cilastatin (cilastatin inhibits renal dihydropeptidase → prevents drug breakdown)
2. Meropenem

MOA: Inhibit cell wall synthesis; broadest β-lactam spectrum.
Uses: Severe mixed infections, ESBL-producing organisms, septicemia, hospital-acquired pneumonia.
Adverse: Seizures (esp. imipenem), nausea, allergy, diarrhea.
Dosage:

Imipenem–Cilastatin: 500 mg IV q6–8h
Meropenem: 500–1000 mg IV q8h

Contraindication: β-lactam hypersensitivity, seizure disorders (use caution).
Interactions: Valproic acid (↓ levels → ↑ seizure risk).

Memory Tip:
“Cephs march from Gram+ to Gram– as generations advance”
1st Gen → Gram+ focus
4th/5th Gen → Gram– + special coverage (Pseudomonas, MRSA)

END OF THE DOCUMENT

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