8. Antibiotics .pptx

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1. Antibiotics

2. Antibiotics Definition – These are the products of one micro-organism which kills or inhibits the growth of other micro-organism without significantly affecting the host cell. Antibiotics is the old term, nowadays the term AMA (Antimicrobial agents) is used because now many synthetic and semisynthetic drugs are available. 2. Classification of AMA - a) Based on Mechanism of Action – (i) Inhibits cell wall synthesis – Penicillin, Cephalosporins (ii) Inhibits protein synthesis – Tetracyclines, Macrolides, Chloramphenicol (iii) Inhibits bacterial DNA gyrase – Quinolones & Fluoroquinolones (iv) Causes misreading of m-RNA code – Aminoglycosides (v) Inhibits folic acid synthesis - Sulfonamides

3. b) Based on Type of organisms – Antibacterial, Antiviral, Antiprotozoal, Antifungal, Anthelmintic c) Based on Spectrum of Activity – (i) Narrow spectrum – Penicillin (ii) Broad spectrum – Ciprofloxacin, Tetracyclines, Chloramphenicol d) Based on Type of action – (i) Bactericidal – Penicillin, Cephalosporins, Aminoglycosides, Fluoroquinolones (ii) Bacteriostatic – Tetracyclines, Sulfonamides, Chloramphenicol

4. Penicillins – - first antibiotic discovered - first obtained from Penicillium notatum but the present source is Penicillium chrysogenum - Beta-lactam antibiotic Mechanism of action – Inhibits cell wall synthesis Narrow spectrum of activity – very effective against the Gram +ve bacteria like Streptococci, Staphylococci, Pneumococci; Gram –ve bacteria like Gonococci, Meningococci and Spirochetes like Treponema pallidum. ADR – Intolerance – Allergy & Anaphylactic reaction Allergy – Skin rashes, Renal disturbances, Haemolytic anaemia Anaphylactic – Cardiovascular collapse, Bronchospasm and angioedema

5. Semisynthetic penicillins – Ampicillin - Dose – 500mg q.i.d. ADR – Diarrhoea b) Amoxicillin – Dose – 500mg tds/q.i.d. c) Cloaxicillin – Dose – 500mg tds/q.i.d.

6. Beta-lactamase inhibitors – Beta lactam is a ring like structure present in antibiotics like Penicillins & Cephalosporins. Beta lactamase is a type of enzyme produced by bacterias like Staphylococci, Gonococci, Haemophilus etc that breaks the beta lactam ring open and deactivates the antibiotic. Beta lactamase inhibitors inhibits beta lactamase enzymes produced by bacteria. Clavulanic acid – 125mg Sulabactum – 0.5mg Tazobactum – 0.5mg

7. Cephalosporins – - Beta lactam antibiotic - derived from fungus Cephalosporinum Mechanism of Action – Inhibits bacterial cell wall synthesis. Generation of Cephalosporins – First Generation Cephalosporins– - highly active against Gram +ve bacterias Examples – Cephalexin, Cephadroxil

8. b) Second Generation Cephalosporins – - Highly active against Gram -ve bacteria Examples – Cefuroxime, Cefaclor. c) Third Generation Cephalosporins – - Highly active against Gram –ve bacteria as well as resistant to Beta lactamase. Examples – Cefixime, Cefotaxime. d) Fourth Generation Cephalosporins – - Spectrum of activity similar to third generation as well as highly resistant to Beta lactamases. Examples – Cefepime, Cefpirome.

9. Macrolides – Mechanism of Action – Inhibits protein synthesis Bacteriostatic – in low concentrations Bactericidal – in high concentrations Examples – Erythromycin – 250-500mg q.i.d. Roxithromycin – 150-300mg b.i.d. Clarithromycin – 250-500mg b.i.d. Azithromycin – 500mg o.d.

10. Aminoglycosides – Highly active against Gram –ve bacteria. Source – Soil actinomycetes Mechanism of Action – Causes misreading of mRNA ADR – Ototoxicity, Nephrotoxicity & Neuromuscular blockade. Examples – Streptomycin – 0.75 to 1gm i.m. twice/thrice weekly Gentamycin – 80mg b.i.d. Amikacin – 0.5 to 1gm o.d.

11. Tetracyclines – - bacteriostatic - broad spectrum antibiotic Mechanism of Action – Inhibits protein synthesis Examples – Tetracycline – 250 to 500mg t.ds./q.i.d. Oxytetracycline - 250 to 500mg t.ds./q.i.d . Doxycycline – 100mg o.d. Minocycline – 100mg o.d.

12. Chloramphenicol – - Bacteriostatic - Broad spectrum antibiotic Mechanism of Action – Inhibits protein synthesis Dosage – 3gm/day in divided doses. ADR - Bone marrow depression, Gray baby syndrome

13. Quinolones- - synthetic antibiotic - mainly active against gram –ve bacteria Mechanism of Action – Inhibits bacterial DNA gyrase, a very important enzyme for DNA replication Example – Nalidixic acid – 500mg t.d.s /q.i.d.

14. Fluoroquinolones - - synthetic antibiotic - bactericidal Mechanism of Action – Inhibits bacterial DNA gyrase Examples – Ciprofloxacin – 500mg b.i.d. Norfloxacin – 400mg b.i.d. Ofloxacin – 200mg b.i.d. Levofloxacin – 500mg o.d.