Antibiotics

General consideration Chemotherapy: treatment of systemic infection with specific drug that selectively suppress the infecting microorganisms without significantly affecting the host. Antibiotics: these are the substances produced by microorganisms which suppress the growth or kill the microorganism at very low concentration.

Classification of antibiotics On the basis of chemical structure Circonamide and related drugs – Sulphadiazine, Sulphone (Dapsone, Paraaminosalicylic acid) Diaminopyrimidine – Trimethoprim, Pyrimethamine Quinolones – Norfloxacin, Nalidixic acid, Ciprofloxacin Beta lactum antibiotics – Penicillins, Cephalosporins, Monobactam, Carbapenems Tetracyclines – Oxytetracycline, Doxycycline Nitrobenzene derivatives – Chloramphenicol Aminoglycosides – Streptomycin, Gentamicin, Neomycin

Classification of antibiotics h. Macrolides antibiotics – Erythromycin, Roxithromycin, Azithromycin Polypeptide antibiotics – Polymyxin-B, Colistin, Bacitracin Glycopeptides – Vancomycin, Teicoplanin Oxyzolidinone – Linezolid Nitrofurantoin derivatives – Nitrofurantoin, Furazolidone Nitroimidazole derivative – Metronidazole, Tinidazole Nicotinic acid derivatives – Isoniazide, Pyrazinamide, Ethionamide Polyene derivatives – Nystatin, Amphotericin-B, Hamycin Azole derivatives - Ketoconazole, Clotrimazole, Fluconazole, Miconazole

II. On the basis of mechanism of action Inhibits cell wall synthesis – Penicillins, Cephalosporins, Cycloserine, Vancomycin, Bacitracin Causes leakage from cell membrane – Polypeptides (polymyxin-B, Bacitracin, Colistin), polyenes (Amphotericin-B, Nystatin, Hamycin) Inhibit protein synthesis – Tetracyclines, Chloramphenicol, Erythromycin, Clindamycin, Linezolid Cause misreading of mRNA code and affects permeability – aminoglycosides, Streptomycin, Gentamicin Inhibit DNA gyrase – Fluoroquinolones (Ciprofloxacin)

Interfere with DNA function – Rifampin, Metronidazole Interfere with DNA synthesis – Acyclovir, Zidovudin Interfere with intermediary metabolism – Sulphonamides, Sulphone, paraaminosalicylic acid, Trimethoprim, Pyrimethamine, Ethambutol

III. Types of organisms against which primarily active Antibacterial – Penicillins, Aminoglycosides, Erythromycin Antifungal – Griseofulvin, Amphotericin-B, Ketoconazole Antiviral – Acyclovir, Zidovudine, Amantadine Antiprotozoal – Chloroquine, Pyrimethamine, Metronidazole, Diloxanide Antihelminthic – Mebendazole, Pyrantel, Niclosamide

IV. According to spectrum of activity Narrow spectrum – Penicillin-G, Streptomycin, Erythromycin Broad spectrum – Tetracyclines, Chloramphenicol

V. According to type of action Primarily bacteriostatic – Sulphonamides, Tetracyclines, Chloramphenicol, Erythromycin, Ethambutol Primarily bactericidal – Penicillins, Aminoglycosides, Cephalosporins, Vancomycin, Ciprofloxacin, Rifampicin, Cotrimoxazole

VI. Antibiotics obtained from Fungi – Penicillin, Griseofulvin, Cephalosporin Bacteria – Polymyxin-B, Colistin, Bacitracin Actinomycetes – Aminoglycosides, Macrolides, Tetracyclines, Polyenes, Chloramphenicol

Side effects of antimicrobial agents Toxicity – Local irritancy - gastric irritation, pain, abscess formation at intramuscular site of injection, thrombophlebitis of injected vein. Systemic toxicity- Aminoglycosides – 8th nerve damage and kidney damage Tetracyclines – liver and kidney damage, anti-anabolic effects Chloramphenicol – bone marrow depression

Hypersensitivity reaction Drug resistance Rashes to anaphylactic shock Commonly with penicllin, sulphonamide, cephalosporin Drug resistance Refers to unresponsiveness of microorganisms to antimicrobial agent and is akin to the phenomenon of tolerance seen in higher organisms 2 types- Natural Acquired