ANTIBIOTICS

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ANTIMICROBIAL AGENTS & ANTIBIOTIC SENSITIVITY TESTS:

ANTIMICROBIAL AGENTS & ANTIBIOTIC SENSITIVITY TESTS

Antimicrobial Agents Include::

Antimicrobial Agents Include: Antibacterial Antiviral Antifungal Antiprotozoal Antihelminthic

Antibacterials:

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:

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

PowerPoint Presentation:

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

PowerPoint Presentation:

ANTIBIOTIC SENSITIVITY TESTS

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

PowerPoint Presentation:

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…..:

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.

AGAR DILUTION:

AGAR DILUTION

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..:

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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