Pharmacology of penicillins

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

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