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Antimicrobial Agents Include::

Antimicrobial Agents Include: Antibacterial Antiviral Antifungal Antiprotozoal Antihelminthic


Antibacterials Antibiotics- natural microbial products Chemotherapeutic agents- synthetic -Synthetic & semi synth. antibiotics also All systemic antibacterials- antibiotics All topical antimicrobials- antiseptics Demonstrate selective toxicity: Bactericidal / bacteriostatic

Activity of Antibacterials:

Activity of Antibacterials Bactericidal Penicillins Cephalosporins Cotrimoxazole Amino glycosides Quinolones Vancomycin Metronidazole Bacterostatic Chloramphenicol Tetracyclines Erythromycin Nalidixic acid Sulfonamides Trimethoprim

Sites of antibiotic action:

Sites of antibiotic action

Sites of action:

Sites of action Cell wall synthesis β lactams – Penicillins (P, A, Clox, Pip) Cephalosporins (generations) Monobactams (astreonam) Carbapenems (imipenem) Glycopeptides (Vancomycin)

Sites of action contd…:

Sites of action contd… Ribosomes (protein synthesis) Tetracyclines (T, Doxy, Mino) Aminoglycosides (Genta, Strepto, Amikacin) Macrolides (Erythro, Clari, Roxi, Azithro ) Chloramphenicol Lincosamide (Clindamycin- Anaerobes) Fusidic acid Linezolid Mupirocin (topical)

Sites of action contd…:

Sites of action contd… Nucleic acid synthesis Sulphonamides & Trimethoprim Quinolones (Nal, Cip, Nor, Gati, Spar) Metronidazole, Tinidazole Nitrofurans (Nitrofurantoin, Furazolidone) Rifampicin Cytoplasmic membrane Polymyxins (polymyxin B, Colistin)


Antifungals Topical Nystatin Azole (Clotrimazole, Micona.., econazole) Tolnaftate Systemic Griseofulvin Azole (ketoconazole, fluconazole) Amphotericin B 5 flurocystein Capsofungin

Antiviral agents:

Antiviral agents I. Agents against viruses other than HIV II. Antiretroviral agents

Agents against V other than HIV :

Agents against V other than HIV Nucleoside analogues - Inhibit viral DNA polymerase activity thus halting viral DNA synthesis Acyclovir, Pencyclovir(H. simplex, V. zoster) Gancyclovir, Cidofovir ( CMV ) Ribaverin, Lamivudine ( HCV, HBV )

Agents against viruses other than HIV contd…:

Agents against viruses other than HIV contd… Viral uncoating blockers Amantadine, Rimantadine (Influenza virus) Neuraminidase inhibitors Zanamivir, Oseltamivir (Infleunza virus) Interferons ( IF a )

Antiretroviral agents:

Antiretroviral agents Nucleoside RTI (rev. transcrip. Inhibitors) Zidovudine, Lamivudine, Stavudine Didanosine, Zalcitabine Abacavir Non-nucleoside RTI Nevirapine, Delaverdine, Efavirenz Protease inhibitors Indinavir, Amprenafir, Retonavir, nelfinavir

Antiprotozoal :

Antiprotozoal Metronidazole, Tinidazole Diloxanide furoate, Emetine Choroquine, Quinine, Primaquin, Mefloquine, Pyrimethamine, Proguanil, Artemisinin ….. Melarsoprol, Suramin, Pentamidine Sodium stibogluconate, Amphotericin B

Antihelminthic :

Antihelminthic Piperazine Pyrantel palmoate Mebendazole, Albendazole Levamisole Niclosamide Praziquantel

Spectrum of activity:

Spectrum of activity NARROW SPECTRUM ANTIBIOTICS Penicillin - Gram positive bacteria Gentamicin (Aminoglycosides) - Gram neg. Metronidazole - Anaerobes, Protozoa

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BROAD SPECTRUM ANTIBIOTICS Active against many G + and G - bacteria Tetracyclines Ampicillin Cephalosporins Quinolones Used for blind therapy Much abuse of these agents in clinical practice

General principles of use of antibiotics:

General principles of use of antibiotics 1. Is there evidence Infection? 2. Is the infection likely / unlikely to respond to treatment? 3. Relevant specimens before treatment ? Blood Culture- Septicemia; PUO Exception- Bacterial meningitis in G.P

Gen. principles contd…:

Gen. principles contd… 4. Timing the start of treatment? Life threatening infections - As soon as specimens are collected. Others - Treat symptoms & wait for culture & sensitivity report.

Gen. principles contd…:

Gen. principles contd… 5. Which drug? Specific infections- Narrow spectrum (Less likely to disturb patients’ normal flora) Broad spectrum- Super infection or spread of resistance 6 . Site of infection 7 . Pharmacodynamics of the drug 8 . Patient factors

Combinations of antibiotics:

Combinations of antibiotics Increased side effects & toxicity Super infection with resistant strains Antagonism Increased cost

Effects of antibiotic combinations:

Effects of antibiotic combinations Cidal + cidal – Synergistic Static + cidal – Antagonistic Static + static – Additive Often impossible to predict the effect of a particular combination against a particular isolate

Combinations useful in:

Combinations useful in 1. Mixed / unknown infections Abdominal sepsis – Cephal + Metronidazole 2. Synergistic combinations Penicillin + Genta – Infective endocarditis Septicemia in neutropenic patients 3. Prevention/ Delay of drug resistance Anti-tuberculous drugs - always 3. Genta + Piperacillin – Pseudomonas inf.

Antibiotic prophylaxis:

Antibiotic prophylaxis Over used for prophylaxis. Broad spectrum drugs often misused. spread of resistance in bacterial strains. Narrow spectrum drugs advised for prevention of specific infections. Differentiate prophylaxis & early treatment.

Indications for antibiotic prophylaxis:

Indications for antibiotic prophylaxis Medical Indications: Rheumatic fever - long term oral penicillin Meningococcal meningitis - Close contacts Rifampicin. Recurrent UTI – Low dose, long term Cotrimoxazole / Trimethoprim

Surgical Indications for prophylaxis:

Surgical Indications for prophylaxis Elective Clean Surgeries - No antibiotics. Surgery in ischemic arterial disease – penicillin in amputation, hip surgery Prevention of endocarditis in dental patients- High dose oral amoxycillin 1 hr before procedure.

Surgical Indications contd…:

Surgical Indications contd… Tetanus - Wound toilet, Penicillin, Immuno prophylaxis. Colorectal Surgery – Bowel preparation, Metronidazole, G / Ceph, perioperatively. Splenectomy- Long term penicillin

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Microbiological investigations in antibiotic therapy:

Microbiological investigations in antibiotic therapy 1.Rapid presumptive microbiological diagnosis . Gram stain. Rapid antigen detection. DNA Probes, PCR

2. Antibiotic Sensitivity / resistance predictable:

2. Antibiotic Sensitivity / resistance predictable A. Predictable Sensitivity: Strep. Pyogenes - Penicillin, Erythromycin Enterococci - Ampicillin Candida albicans- Nystatin / Amphotericin. Pneumococci - Penicillin. Staph. aureus - Cloxacillin Severe / hospital infections – unpredictable ABST must

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B. Predictable resistance: Streptococci - Gentamicin Enterococci - Nalidixic acid Pseudomonas - Penicillins, Cephalosporins E. coli - Penicillin Anaerobes - Gentamicin, Ciprofloxacin

3. Antibiotic Sensitivity tests:

3. Antibiotic Sensitivity tests Predict the usefulness of antibiotics when used at usual therapeutic doses. Sensitivity test in vitro does not correlate with clinical results. Generally a drug resistant by ABST, will not be useful for treatment. Serious infections – treat only according to ABST.

Primary (direct) ABST test:

Primary (direct) ABST test Test done directly with the specimen after a Gram stain. Discs placed on agar plates inoculated with the specimen (e.g. CSF) Unsuitable for specimens having normal flora or mixed bacterial growth. Sensitivity result – obtained in 24 hrs.

Secondary (indirect) ABST:

Secondary (indirect) ABST Done with pure cultures Results after 48 hrs or more Should be careful about: Selection of bacteria Inoculum density Standard non inhibitory media (MHA) Standard discs Conditions of incubation


ABST….. Good Controls should be used - Quality control programmes. Kirby Baeur Technique- commonly done. Stoke’s method of ABST (inbuilt control) Special methods for - Mycobacteria, Fungi

Kirby Baeur Technique:

Kirby Baeur Technique

Kirby Baeur Technique:

Kirby Baeur Technique

Stoke’s method:

Stoke’s method

Rapid tests of ABST:

Rapid tests of ABST Chromogenic Tests β lactamase enzyme- Haemophilus, Staph. Chloramphenicol resistance in Haemophilus Automated systems using new technologies Fluorescent methods Laser imaging Results available with MIC in 6 hrs. Very useful in guiding therapy.

Special methods:

Special methods Minimum Inhibitory Concentration (MIC) Minimum Bactericidal Concentration (MBC) Macro broth dilution method: Tube dilution - one bacteria & one antibiotic Micro broth dilution method: In plastic trays - many AB can be tested in serial two fold dilutions in a single tray- Commercially available

MIC by Macro broth dilution:

MIC by Macro broth dilution

MIC & MBC by Macro broth dilution:

MIC & MBC by Macro broth dilution No AB No inoculum Neat 1 / 2 1 / 4 1 / 8 1 / 16 1 / 32 1 / 64 MBC MIC

MIC by Microdilution:

MIC by Microdilution

Agar Dilution method:

Agar Dilution method For testing MICs of a large number of isolates against many concentrations of several antibiotics. For testing susceptibility of mycobacteria- Middle-brook 7H11 agar.



E- test:

E- test Antimicrobial Gradient Strip Method. Recently described Variant of disc diffusion technique. Quantitative determination of MICs on Agar. Plastic strip containing a gradient of AB on one side & interpretive scale one the other. Very useful. Can be adapted to any agar medium & most micro organisms.

Epsilometer-test (E-test):

Epsilometer-test (E-test)

E-TEST …..:

E-TEST …..

Checker Board / Chess Board technique:

Checker Board / Chess Board technique To find out synergistic combinations of antibiotics. The least dilution of combination drugs which inhibit the bacterial growth is known as Fractional Inhibitory Concentration. ( FIC)

Checker board:

Checker board

Measurement of antimicrobial levels in body fluids:

Measurement of antimicrobial levels in body fluids Therapeutic Drug Monitoring (TDM) . Commonly called - Antibiotic Assays. Done for 2 reasons. 1. Whether effective level of antimicrobial is achieved?- Serum, CSF/ other fluids. (Peak level/ Post dose Serum) 2. Whether toxic levels reached? – Trough level /Pre dose serum.(Aminoglycosides)


TDM.. Initially only bio assays were done- 24 hrs. Automated Methods- chemical/ immunological- Few hrs. Gas liquid chromatography High pressure liquid chromatography Radio immunoassay Competitive binding Immunoassay

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