Penicillins
Penicillins are β-lactam antibiotics derived from Penicillium fungi. They kill bacteria by interfering with cell wall synthesis and are among the most widely used antibiotics.
Pharmacodynamics
- Penicillins bind to Penicillin-Binding Proteins (PBPs) on bacterial cell membranes.
- PBPs are enzymes needed for cross-linking the peptidoglycan layer in bacterial cell walls.
- Inhibiting PBPs leads to weakened walls, causing bacterial lysis and death.
- Their action is bactericidal (requires bacteria to be actively dividing).
Side Effects
Common:
- Nausea, vomiting, diarrhea
- Abdominal pain
- Skin rashes
- Allergic reactions
Rare but serious:
- Anaphylaxis
- Stevens-Johnson Syndrome
- Interstitial nephritis
- Liver toxicity
- Blood disorders (e.g., hemolytic anemia)
Drug Interactions
- ↓ Oral contraceptive effectiveness
- ↑ Warfarin effect → ↑ bleeding risk
- Probenecid ↑ penicillin levels by ↓ renal clearance
- Inactivation of aminoglycosides if mixed in same IV solution
- Tetracyclines antagonize the effect of penicillins (bacteriostatic vs. bactericidal)
Therapeutic Uses
- Respiratory tract infections: Pneumonia, bronchitis, pharyngitis, sinusitis
- ENT infections: Otitis media, sinusitis
- Skin/soft tissue: Cellulitis, impetigo
- UTI: Cystitis, pyelonephritis
- GI infections: Enteric fever, bacterial gastroenteritis
- STDs: Syphilis, gonorrhea
- CNS: Meningitis
- Bone and joint: Osteomyelitis, septic arthritis
- Cardiovascular: Endocarditis