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Beta-Lactam Antibiotics: Classification, Mechanism, and Therapeutic Uses
Classification
- Penicillins: Penicillin G, Penicillin V, Aminopenicillins, Penicillinase-resistant penicillins, Extended-spectrum penicillins.
- Cephalosporins: Divided into five generations, e.g., cefazolin (1st gen), ceftriaxone (3rd gen), cefepime (4th gen), and ceftaroline (5th gen).
- Carbapenems: Imipenem, Meropenem, Ertapenem.
- Monobactams: Aztreonam.
Mechanism of Action
Beta-lactam antibiotics inhibit bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), preventing peptidoglycan formation, leading to bacterial lysis and death.
Mechanism of Resistance
- Beta-lactamase production: Enzymes that break the beta-lactam ring, rendering the antibiotics ineffective.
- Alteration of PBPs: Reduced affinity for beta-lactams.
- Reduced permeability: Decreased drug entry, particularly in gram-negative bacteria.
- Efflux pumps: Active expulsion of antibiotics from bacterial cells.
Therapeutic Uses
- Respiratory infections (pneumonia, bronchitis)
- Urinary tract infections
- Skin and soft tissue infections
- Meningitis, endocarditis, sepsis
- Intra-abdominal infections, gonorrhea, syphilis
Adverse Effects
- Allergic reactions (rashes, anaphylaxis)
- Gastrointestinal disturbances (nausea, diarrhea)
- Hematological effects (leukopenia, thrombocytopenia)
- Hepatic toxicity (elevated liver enzymes)
- Renal toxicity (especially methicillin)
- Seizures (carbapenems in high doses)
Contraindications
- Allergy to penicillins or cephalosporins (cross-reactivity)
- Renal impairment (requires dose adjustment)
- Pregnancy and lactation (most are safe, but medical supervision is advised)
