Study Guide Ch. 20 Flashcards
Explain what a chemotherapeutic antimicrobial agent is.
agent is used to decrease the growth of microbes using chemical treatments
Explain the characteristics that a good chemotherapeutic agent or antibiotic should have.
o Good chemotherapeutic agents and antibiotics should
have selective toxicity (Toxic to microorganisms but not to me)
o cause mild or no secondary reactions (side effects) (treatments are indicated when the risk of illness is greater than treatment risk)
o be stable at room temperature (storage) and body temperature (use)
o tolerate stomach acid
o not interact with food
o be metabolically stable in the body
o be effectively absorbed and distributed where needed
Define selective toxicity, toxic dose and therapeutic dose.
o Selective Toxicity: a drug should harm the pathogen but not the host.
o Toxic Dose: the concentration of a drug that is causing harm to the host.
o Therapeutic Dose: the concentration that is eliminating pathogens in the host.
Explain what the chemotherapeutic index is, how is it formulated and what does a high or low number mean
o The index is toxic dose/therapeutic dose
o Toxic dose should be higher then therapeutic dose always
o Want to keep the index dose over 1, the higher the better
List and define the different sources of chemotherapeutic antimicrobial agents.
Synthetic agents- chemical drugs made in lab
Antibiotics- products of or derived from living microorganisms
Semisynthetic drugs- include synthetic and antibiotic elements
List and define the different types of antimicrobial agents by target organism.
o By Target Organism:
Antibacterial: based on prok structure and metabolism
Antifungal: may cause more side effects because cells are euks. The challenge is to look for differences (they have a cell wall)
Antiparasitic: animal cells/ animal like
* Antiprotozoan - against unicellular, animal-like protists (amoebas, ciliates and flagellates)
* Antihelminthic - against multicellular worms
Antiviral: Hardest one because they replicate using our stuff
Differentiate between broad-spectrum antibiotic and narrow-spectrum antibiotic.
o Broad spectrum: Drugs affect many taxonomic groups
o Narrow Spectrum: Drugs effect only few pathogens
Explain the mechanisms of action by which chemotherapeutic agents and antibiotics may act.
o By mechanism of action:
Cell wall synthesis: inhibition renders the cell susceptible to osmotic shock
DNA or RNA synthesis: inhibition of replication or transcription
Protein synthesis: inhibition of translation
Cell membrane function: disrupting affects membrane permeability and causes leakage of cell content
Cell metabolism: Affecting metabolic reactions specific for the microorganisms
Explain why sulfonamides and isoniazid are not antibiotics.
Because they are not naturally produced by microorganisms
Know that the nomenclature of antiviral agents either includes a “vir” (e.g. acyclovir or maraviro) or ends in “ine” (e.g. azidothymidine (AZT) or dideoxycitidine).
o Always formatted this way
o Look for virs and ines and know it is an antiviral
Recognize that the following are examples of antifungal agents: nystatin, amphotericin B and griseofulvin.
o Nystatin: membrane damage; polyenes bind to ergosterol causing contents to leak, kills athletes’ foot
o Amphotericin B: membrane damage; polyenes bind to ergosterol causing contents to leak, very toxic, can cause liver damage
o Griseofulvin: Inhibits microtubule formation
- Recognize that the following are examples of antiparasitic agents: aminoquinoline (antimalarial), sulfonamides (antiprotozoans), nitroimidazoles (e.g. metronidazole is antiprotozoan and anti-anaerobic bacteria) and prazinquantel, mebendazole & ivermectin as antiworm drugs.
o Antiparasitic Agents:
Aminoquinoline:
* Interfere with the parasite’s ability to breakdown and digest hemoglobin
* Examples are quinine and chloroquine
* Used to treat malaria
o Antiprotozoans:
Sulfonamides:
* Block folic acid synthesis as they do for bacteria
Nitroimidazoles:
* Metronidazole is the most common example
* Also interferes with nucleic acid synthesis
* Treats Trichomonas, giardiasis, and amebiasis, as well as anaerobic bacteria
o Antiworm Drugs:
Prazinquantel:
* Alters membrane permeability
* Treats tapeworms and flukes (i.e., cestodes and trematodes)
Mebendazole:
* Interfere with nutrient absorption
* Disrupts microtubules and cells division
* Treat intestinal helminths
Ivermectin:
* Paralysis of helminths
* Treats roundworms and mites
Describe the inhibition of folic acid metabolism as an example of inhibition at the metabolic level.
o Sulfonamides, being structurally similar to PABA, act as antimetabolites by binding to the enzyme that would normally bind PABA, thereby blocking the production of folic acid. Without folic acid, bacteria cannot produce essential components for their growth and replication, leading to their inhibition or death
Describe the mechanism of resistance to penicillin based on the breakdown of its beta-lactam nucleus as an example of this phenomenon, and what synthetic chemical changes have created penicillins no longer susceptible to beta-lactamase
o The resistance to penicillin is primarily due to the bacterial production of an enzyme called penicillinase (also known as β-lactamase). This enzyme breaks down the β-lactam ring, a critical structure in penicillin, rendering the antibiotic ineffective
o Semisynthetic penicillins have been developed. These penicillins have chemically added side chains that make them resistant to the action of β-lactamase
Describe the mechanism of action (inhibitory mechanism) or the following antimicrobial agents:
o Penicillin, cephalosporin, vancomycin, bacitracin and isoniazid- Antibiotics
o Polymyxi B- Damages membranes
o Chloramphenicol, aminoglycosides (e.g. streptomycin) macrolides (e.g. erythromycin) & tetracycline.- Inhibits Protein Synthesis
o Quinolones and Rifampin- Nucleic Acid Synthesis Inhibitors
o Sulfonamides- Inhibits Folic Acid
