Chapter 10 Controlling Microbial Growth in the Body: Antimicrobial Drugs

I.  Definitions

A.     Chemotherapeutic agent- any agent that inhibits growth, including manmade agents

B.     Antibiotic- an antimicrobial agent produced by another living organism

C.     Antibiogram- characteristic pattern of resistance

D.     Resistance vs Sensitivity

E.     Bacteriocidal versus bacteriostatic

  II.        Antimicrobial Characteristics

            A. Toxicity - may require blood levels

            B.  Action - method of inhibition affecting microbe, best if it selectively targets procaryotic cells

            C. Spectrum - narrow (GN or GP or even a particular species e.g. anti-mycobacterial)

            D. Target Tissue - selective concentration of a particular antimicrobial e.g. Nitrofurantoin and Gantrisin in bladder, Zithromycin in deep tissues

            E. Adverse effects

                    1. Allergies - some life threatening - medic bracelet

                    2. Side effects - rashes, nausea, dry mouth

                    3. Normal flora - may destroy balance

            F. Development of resistance - plasmid transfer of resistance factors

                    1. High Concentration of the drug inhibits development of resistance - stopping prescriptions before     finishing encourages resistance.

                    2. Combination therapy - synergism - can combat development of resistance

                    3. Limited use of antimicrobials reduces resistance

                    4. New drug development is expensive, but overcomes resistance

            G. Cost - newest and non-generic drugs have heavy R&D embedded cost

            H. Administration - Topical, Oral, IM, IV

III. Mechanisms of Antimicrobial Drugs

IV. Types of Agents - This is linked to the antibiotics we will use in class

Antibiotic Names of common drugs Target Organisms & Infections Special Concerns
Drugs that target cell wall synthesis - beta lactams and betal lactamase**

Penicillins - interrupt linkages of peptidoglycan

 Penicillin, Ampicillin Carbenicillin, Amoxicillin, Methicillin Gram Positive organisms Allergies

Beta lactamase

Cephalosporins

 Cephalexin, Cefaclor, Cefexim GN & GP  more resistant to Beta lactamase

Carbapenems
 

 Imipenem GN & GP most resistant to Beta lactamase

Vancomycin

 Vancomycin GP Last line against MRSA

Bacitracin

 Bacitracin GP & GN only used topically

Drugs that target protein synthesis

Aminoglycosides

binds to ribosomes blocks translation

 Streptomycin, Gentamicin, Tobramycin, Neomycin (topical only) Broad spectrum but often used synergistically with cephalosporins severe hearing and kidney damage

must draw blood levels

 

Tetracyclines

blocks tRNA stopping protein synthesis

 Tetracycline, Minocycline, Doxycycline Only works on procaryotic cells Sun sensitivity, bone and tooth damage in children

Macrolides

prevent protein synthesis by binding to ribosomes

 Erythromycin, Zithromycin Mycoplasma,

GP, some GN

 Used for Penicillin allergic patients

Chloramphenicol

prevents peptide  synthesis bonding by ribosomes

 Chloramphenicol Broad spectrum May inhibit bone marrow production (aplastic anemia)

Drugs that target nucleic acid synthesis

Fluoroquinolones - inhibit DNA gyrase interupting DNA replication

 Ciprofloxacin, Ofloxacin, Lomefloxacin Very Broad spectrum increasing resistance noted

Rifampin

blocks RNA activity in ribosomes

 none GN and Mycobacteria Quick resistance development
Drugs that inhibit Metabolic Processes
Sulfonamides - imitate PABA and disrupt folic acid metabolism Sulfa drugs

Gantrisin

 GN, some GP allergic reactions, sun sensitivity

Trimethoprim

 SXT, Bactrim Broad Synergistic use of sulfa with trimethoprim - sulfamethaoxazole/trimethoprim

Drugs that target cell membrane integrity

Polymyxin B

 Polymyxin B GN Topical only
Amphotericin B Amphotericin B Fungi Very harsh side effects
Drugs that target AFB - See Sanford Table 11B

Ethambutol - interrupt mycolic acid formation in call wall

Ethambutol

 Mycobacteria used synergistically in multidrug therapy
INH Isoniazid - interrupt mycolic acid formation in call wall INH Isoniazid Mycobacteria used synergistically in multidrug therapy
Clofazimine - prevents replication and transcription Lamprene Mycobacterium leprae  
Drugs that inhibit viral infections - Sanford Table 14 A
Arildone - attachment antagonists   Picornavirus - polio  
Amantadine - inhibits viral uncoating(Symmetrel, Rimantadine, Flumadine)   Influenza CNS side-effects
Ribavirin (Virazole)   RSV Anemia, rash - do not use in pregnancy
Anti-retroviral drugs
Acyclovir family (Famicyclovir, Penciclovir) - Inhibit nucleic acids (Zovirax)   HIV phlebitis and vesicular lesions
Protease inhibitors - blocks active site   HIV  

See Table 6 in Sanford Guide  - Summary of Antimicrobials and Pregnancy

Sanford Guide

V. Antibiotic Effectiveness testing

A.     Kirby Bauer

B.     MIC - provides exact concentration

 

VI. Antibiotic Resistance

A.     MRSA, Pseudomonas, VRE

B.     Abuse

1.      Artificial selection

2.      Developing countries

3.      Animal feed -

VII. Antiviral Drug Mechanisms

           

            A. Viral Uncoating

            B. Nucleic Acid Analogs

            C. Protease Inhibitors

   D. Refer to Text Book Table 10.3

VIII. Antifungal Drug Mechanisms

            A. Plasma Membrane disruption

IX. Antiparasitic Drug Mechanisms

A.    Plasma membrane disruption

B.     Interruption of cell division

C.     Inhibition of nucleic acid synthesis

D.    Refer to Textbook table 10. 4

IX. Antiprotozoal Drugs & Mechanisms

A.    Heavy Metals – interfering with protein shape and reactivity

B.     Quinine – inhibits DNA synthesis

C.     Sulfonamides & Trimethoprim– competitive inhibitor for specific enzymes

D.    Nitroimidazoles – e.g. Metronidazole

E.     See Textbook table 10.6

 

 

X. Anti-Helminthic Drugs

          A. Mebendazole – inhibits enzymes in Mitosis

          B. Praziquantel & Piperazine – paralyses worms

          C. Niclosamide – inhibits ATP

          D. See textbook table 10.5

 

Chapter 10 Controlling Microbial Growth in the Human Body Antimicrobial Drugs

 

1. Describe the mechanism of competitive inhibition using the example of sulfanilamides to interrupt the growth of bacteria.
2. Describe the action of antimicrobials in the penicillin family and drawbacks to their use.

3. Compare the cephalosporin and penicillin antibiotics with respect to source, structure, spectrum of activity, and side effects.

4. When given a clinical infection, use the Sanford guide to determine the empirical treatment and potential side effects.

5. State several examples and describe the chemical structure, uses, and side effects of tetracycline antibiotics.

6. Explain the unique dosage and use of antimicrobials for Mycobacterial infections.

7. Draw a bacterial cell and indicate the physical area or pathways affecting by each of the major groups of antibiotic families.

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