Transcript Chapter 20b

B.E Pruitt & Jane J. Stein
Chapter 20, part B
Antimicrobial Drugs
Antifungal Drugs
Inhibition of Ergosterol Synthesis
• Polyenes
• Amphotericin B
• Azoles
• Miconazole
• Triazoles
• Allylamines
Figure 20.15
Antifungal Drugs
Inhibition of Cell Wall Synthesis
• Echinocandins
• Inhibit synthesis of -glucan
• Cancidas is used against Candida and
Antifungal Drugs
Inhibition of Nucleic Acids
• Flucytocine
• Cytosine analog interferes with RNA synthesis
• Pentamidine isethionate
• Anti-Pneumocystis; may bind DNA
Antifungal Drugs
Inhibition of Microtubules (Mitosis)
• Griseofulvin
• Used for superficial mycoses
• Tolnaftate
• Used for athlete's foot; action unknown
Antiviral Drugs
Nucleoside and Nucleotide Analogs
Figure 20.16a
Antiviral Drugs
Nucleoside and Nucleotide Analogs
Figure 20.16b, c
Antiviral Drugs
Enzyme Inhibitors
• Protease inhibitors
• Indinavir
• Inhibit attachment
• Zanamivir
• Relenza
• Inhibit uncoating
• Amantadine
• Oseltamivir
• Tamiflu
• Interferons prevent
spread of viruses to
new cells
• Viral hepatitis
Antiprotozoan Drugs
• Chloroquine
• Inhibits DNA synthesis
• Malaria - may require Malarone
• Diiodohydroxyquin
• Unknown
• Amoeba
• Metronidazole
• Damages DNA
• Entamoeba, Trichomonas
Antihelminthic Drugs
• Niclosamide
• Prevents ATP generation
• Tapeworms
• Praziquantel
• Alters membrane permeability
• Flatworms
• Pyantel pamoate
• Neuromuscular block
• Intestinal roundworms
Antihelminthic Drugs
• Mebendazole
• Inhibits nutrient absorption
• Intestinal roundworms
• Ivermectin
• Paralyzes worm
• Intestinal roundworms
Evaluation of Antimicrobials-Disk-Diffusion Test
Figure 20.17
Action on growth after transfer to new media
Minimal inhibitory concentration
Minimal bactericidal concentration
Broth Dilution Test
Figure 20.19
Figure 20.20
Antibiotic Resistance
• A variety of mutations can lead to antibiotic resistance.
• Mechanisms of antibiotic resistance
1. Enzymatic destruction of drug
2. Prevention of penetration of drug
3. Alteration of drug's target site
4. Rapid ejection of the drug
• Resistance genes are often on plasmids or
transposons that can be transferred between bacteria.
Antibiotic Resistance
• Misuse of antibiotics selects for resistance
mutants. Misuse includes:
• Using outdated, weakened antibiotics
• Using antibiotics for the common cold
and other inappropriate conditions
• Use of antibiotics in animal feed
• Failure to complete the prescribed
• Using someone else's leftover
Effects of Combinations of Drugs
• Synergism occurs when the effect of two drugs
together is greater than the effect of either alone.
• Antagonism occurs when the effect of two drugs
together is less than the effect of either alone.
Effects of Combinations of Drugs
Figure 20.22
The Future of Chemotherapeutic Agents
• Antimicrobial peptides
• Broad spectrum antibiotics from plants and animals
• Squalamine (sharks)
• Protegrin (pigs)
• Magainin (frogs)
• Antisense agents
• Complementary DNA or peptide nucleic acids that
binds to a pathogen's virulence gene(s) and
prevents transcription