Oct 30, 2010

Chemotherapy & Classification of Antimicrobials

  • It is the branch of Pharmacology which deals with drugs which selectively inhibit or destroy specific pathogenic organisms like bacteria, viruses, fungi and parasites.
  • This term is extended to the use of drugs in the treatment of neoplastic diseases because of similarity between the malignant cells and the pathogenic microbes.
  • The term was first used by Paul Ehrlich in 1913 to describe drugs which attack invading organisms without harming the host.
Terms and Concepts
Chemotherapeutic Agents
The drugs used to interfere with the functioning of foreign cells.
Chemical substances produced by various micro organisms that kill or suppress growth of other micro organisms.
All chemical substances whether natural, synthetic or semi-synthetic that kill or suppress the growth of micro organisms
Selective Toxicity
It is the ability of an antimicrobial agent to kill an invading microorganism without harming the cells of the host.
Antimicrobial Activity
Refers to the ability of a compound to react with the microbial cell molecules in a way that interferes with growth and multiplication of microorganism or causes killing of the microorganism
Bacteriostatic Activity
It is the ability of the antibacterial agent to inhibit the growth and multiplication of bacteria.
Bactericidal activity
It is the ability of an antimicrobial agent to cause the death of the bacteria.
Antimicrobial Spectrum
Refers to the range of pathogenic organisms against which an antimicrobial agent is active.
B.S.A.M. are active against a wide variety of organisms.
N.S.A.M. are active against a few or a class/type of organisms.
Narrow Spectrum
Active against a few or class/type of organisms e.g, G + ve or G-ve.
Broad Spectrum
Active against a wide variety of organisms e.g.  both G + ve & G-ve.
Defined as the antimicrobial activity per miligram (microgram) of a chemotherapeutic agent
Expressed in:
All are determined in vitro.
Minimum Inhibitory Concentration (MIC)
It is the lowest concentration which prevents visible growth of bacteria when grown on serial dilutions in vitro.
Minimum Bactericidal Concentration (MBC)
Lowest concentration which kills the bacteria
Minimum Antibiotic Concentration (MAC)
Concentration which reduces the growth of an organism in vitro by factor of 10 (e.g. one log)
Used to express the activity of some drugs that exert antimicrobial action in vivo at conc. Below the MIC
Post Antibiotic Effect (PAE):
Effect even after antibiotic is out.
Biphasic (EAGLE) Effect
Effect at low doses but not at high doses
Properties of an ideal Antimicrobial Agent (AMA)
  • Powerful action against micro organisms
  • Selective toxicity
  • Slow metabolism
  • Well distributed in the body
  • Good oral bio availability
  • Long elimination half life
  • No bacterial resistance or cross resistance
  • No effect on the host immune system
  • No adverse drug interaction
  • No/Short withdrawal period in food producing animals
  • Economical and easily available
Classification of antimicrobial agents
Based on Mechanism of Action
Inhibit Cell Wall Synthesis: Penicillin, cephalosporin, cycloserine, bacitracin, vancomycin & clotrimazole.
Inhibit Cytoplasmic Membrane Function: polymyxins, amphotericin B & nystatin.
Inhibit protein synthesis: Chloramphanicol, tetracycline, macrolides and aminoglycosides.
Interfere with Intermediary Metabolism: sulphonamides, trimethoprim and sulphons.
Affect nucleic acid metabolism and synthesis: quinolones, rifampicin, and acyclovir
Based on Chemical Structure
sulphadimadine, sulphadiazine, sulphanilamide, sulphaquinoxalone.
Trimethoprim, ormetoprim and baquiloprim
Nalidixic acid, enrofloxacin, difloxacin and ciproflaxocin
Beta-lactam antibiotics:
Penicillin G, ampicillin, cloxacillin, cephazolin, cephalexin
streptomysin, gentamicin, amikacine, tobramycin
Oxytetracycline, tetracycline, doxycyline, minocycline
Macrolide Antibiotics:
Erythromycin and Azithromycin
Nitrofuran – Derivatives:
Nitrofurantoin and furazolidone
Metronidazole and Imidazole
Polypeptide Antibiotics:
Polymyxin B, Colistin and bacitricin
Polyene Antibiotics
Nystatin and amphotericin B
Imidazole derivatives
Ketoconazole, fluconazole and clotrimazole
Based on Therapeutic Uses (Type of Organism)
Penicillin, aminoglycosides, tetracycline, & chloramphenicol,
Amphotericin B, griseofuvin and ketoconazole
Idoxuridine, vidarabine, zidovudine, and ribavirin
Metronidazole, quinapyramine and diminazine
Albendazole, levamisole, niclosamide and praziquntel
Cypermethrin, lindane, amitraz and ethion
Based on Spectrum of Activity
Narrow spectrum antimicrobials:
Penicillin G, streptomycin, erythromycin and vancomycin
Broad Spectrum Antimicrobials:
Tetracycline, chloramphenicol, cephalexin, gentamycin, ampicllin
Based on type of Action
Sulphonamides, chloramphenicol, erythromycin, trimethoprim, clindamycin
Penicillin G, cephalexin, streptomycin, vancomycin, bacitracin and  potentiated  sulphonamides
Based on Source
Natural and Semi-synthetic
Penicillin G, griseofulvin and cephalexin
Streptomycin, tetracycline, erythromycin and    chloramphenicol
Polymyxin B, Colistin and bacitracin
Sulphonamides, trimethoprim, quinolones, nitrofurans and nitro-imidazoles


chota said...

sir gareb bando p tars khayen....itne drugs ka koi tuk nh banta ak dvm studnt k lye,jis ne after degree sirf bazo he dalna hota

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