Mechanism of action, pharmacokinetics, adverse effects and uses of Penicillins.

1. Penicillins

2. Introduction
• The first antibiotic developed and used.
• Discovered accidentally by Alexander Fleming.
• Source: Penicillium chrysogenum
• Structure:

3. Mechanism of action
Penicillin Binds and inactivates penicillin binding proteins on the
cell wall of susceptible bacteria
Inhibits transpaptidase
Preventsts peptidoglycan synthesis
Cell wall deficient forms(Spheroplasts and filamentous forms)
Autolysis
Cell death

4. Pharmacokinetics
• Administration: Intravenous route ( orally administrated penicillin G is
destroyed by gastric acid)
• Distribution: widely in body tissues, poorly crosses the BBB
• Excretionn: In urine by active tubular secretion.

5. Adverse reactions of penicillin G
• Hypersensitivity reactions: skin rashes, utricaria, fever, dermatitis,
bronchospasm, angioedema, joint pain, bserum sickness or
anaphylactic reactions, severe hypotension, laryngeal oedema
• Cross reactivity may occur among penicillins and among Beta-lactam
antibiotics.
* Note: Anaphylactic shock is not dose related adverse reaction, it’s an
immunoglobulin E ( IgE) mediated immediate type of hypersensitivity
reaction.

6. Therapeutic uses
• In dentistry: Vincent’s angina, necrotizing gingivitis etc.
• Pneumococcal infections: pneumonia, meningitis etc.
• Streptococcal infections: pharyngitis, otitis, rheumatic fever etc.
• Meningococcal meningitis
• Gonococcal infections
• Syphilis
• Diphtheria
• Clostridial infections: tetanus, gas gangrene

7. Limitations
• Acid labile
• Short duration of action
• Narrow spectrum of antibacterial activity
• Destroyed by penicillinase enzyme
• Anaphylaxis

8. Contraindications
• In patient with allergic reactions
• Asthma, allergic rhinitis, hay fever

9. Mechanism of bacterial resistance
• By producing Beta-lactamase, destroy Beta-lactam ring
• Due to altered PBPs, have less affinity for Beta-lactam
• Due to decreased ability of the drug to penetrate to it’s site of action

10. Thank you