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63 Cards in this Set
- Front
- Back
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What is the goal of antimicrobial chemotherapy?
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to administer drug to infected person that can destroy the infectious agent and leave the host cells alone
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What must a drug be?
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be easy to administer; able to reach the infectious agent in the body; be toxic to infectious agent and nontoxic to host; remain in the body as long as needed, yet be safely and easily broken down and excreted (-sidal)
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What is a chemotherapeutic drug?
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any chemical used in the treatment, relief, or prophylaxis of a disease
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What is prophylaxis?
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use of a drug to prevent imminent infection of a person at risk
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What is antimicrobial chemotherapy?
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the use of chemotherapeutic drgus to control infection
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What are antimicrobials?
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an all-inclusive term for any antimicrobial drig, regardless of its origin
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What are antibiotics?
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substances produced by the natural metabolic processes of some microorganisms that can inhibit or destroy other microorganisms
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What are semisynthetic drugs?
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drugs that are chemically modified in the laboratory after being isolated from natural sources
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What are synthetic drugs?
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drugs produced entirely by chemical reactions
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What are narrow spectrum drugs?
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limited spectrum drugs; antimicrobials effective against a limited array of microbial types; Ex. a drug effective mainly on gram-positive bacteria
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What are broad spectrum drugs?
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extended spectrum; antimicrobials effective against an wide variety of microbial types; Ex. A drug effective against both gram+ and gram- bacteria
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What are antibiotics common metabolic products of?
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aerobic bacteria and fungi
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What are antibiotics produced to do?
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inhibit the growth of competing organisms
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What are antibiotics derived from?
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Bacteria in the genera Streptomyces and Bacillus; Molds in the genera Penicillum and Cephalosporium
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What do we need to know before we treat a patient?
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nature of the organism(s) you are fighting that is causing the infection; drug sensitivity of agent; patient history (liver and kidney)
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How do doctors identify the agent?
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identify from patient specimens- doctors use test data or an informed guess
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Why is it necessary for testing for drug sensitivity/ susceptibility?
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necessary for bacteria commonly showing resistance
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What is it difficult and unnecessary for?
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fungal or protozoan infections
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What is a technique used for testing drug susceptibility? Describe
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kirby bauer; agar plate is spread bacteria, small discs containing prepared amount of antibiotic are placed on the plate, zone of inhibition- measure
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What is an antibiogram?
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it provides data for drug selection
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What is kirby bauer not ideal for?
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anaerobes, fastidious (finicky) bacteria, slow growing bacteria
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What is another test that more sensitive and accurate?
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tube dilution tests
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What do you do for this test?
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antimicrobial is diluted serially in tubes of broth; each tube is inoculated with uniform sample of pure culture
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What is MIC?
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minimum inhibitory concentration: the smallest concentration of drug that visibly inhibits growth
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What is MIC useful for?
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determining the effective dose
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What is treatment failure due to?
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in vitro (outside body): activity of drug not always correlated with the in vivo effect (inside body)
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What is failure of antimicrobial treatment due to?
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drug can't diffuse to body compartment; resistant microbes not collected for testing; mixed infection
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What is the therapeutic index?
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the ratio of the toxic dose compared to its minimum effective (therapeutic) dose
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What is a better therapeutic index?
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the smaller the ratio the greater the potential for drug reactions
1.1 is risky 10 is safer -the drug with the highest therapeutic index has the widest margin of safety =toxic does/therapeutic dose |
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How do you decide on a course of treatment?
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physician must take a careful history before prescribing antibiotic: patient history, age, other drugs patient is taking, how medication can be taken, cost
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What are the goals of antimicrobial drugs?
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to disrupt cell processes of bacteria, fungi or protozoa; inhibit virus replication; interfere with the function of enzymes required to synthesize or assemble macromolecules; destroy structures already formed in the cell
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What is a selectively toxic drug?
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it can kill/ inhibit the actions or synthesis of molecules in microorganisms but not in vertebrate cells (host cells)
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What do drugs with excellent selective toxicity do?
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block the synthesis of the bacterial cell wall
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What drugs are most toxic to humans?
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drugs that act upon a structure common to both the infective agent and the host cell
-common with microbe cells: DNA cells membrane- could potentially affect us |
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What are the antimicrobial drug categories?
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-inhibit cell wall synthesis; inhibition of nucleic acid structure and function; inhibition of protein synthesis; interference with cell membrane structure and function; inhibition of folic acid (puts together a nucleic acid) synthesis
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Broad spectrum vs narrow spectrum drugs
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effective against a large number of bacterial types;
target a specific group |
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Why do eukaryotic cells present special problems in chemotherapy?
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only a few agents with special antifungal properties have been developed
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What agents are used to treat fungal infections?
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Macrolide polyenes: attach fungal membranes
Azoles: sterile sunthesis Echinocandins: cell wall synthesis Nucleotide cytosine analog: DNA/RNA -more similar a microbe is to us, the harder it is to kill it |
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What antimalarial (antiparasitic) drug is used?
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Quinine
has been replaced by synthesized quinolones, chloroquine and primaquine malaria is caused by genus plasmodium |
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What chemotherapy for other protozoan infections is used?
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Metronidazole; it is widely used amoebicide (eukaryotic=similar to humans)
-treats intestinal infections and hepatic disease caused by Entamoeba hystolytica |
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What are the challenges of antihelminthic drug therapy?
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flukes, tapeworms, round worms, larger parasites; their physiology is much more similar to humans; blocking reproduction does not affect adult worms; most effective drugs kill/destroy all stages of the life cycle
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What are unique challenges in the chemotherapeutic treatment of viruses?
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viruses rely on a host cell for most metabolic functions; disrupting viral metabolism requires disruption of our own cell metabolism and processes; measles, mumps, and hepatitis are prevented through the use of vaccines
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What are the major modes of action of antiviral agents?
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block penetration of the virus into the host cell; blocking transcription and translation of viral molecules; preventing maturation of viral particles
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What is drug resistance?
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An adaptive response- microorganisms tolerate a drug that would normally be inhibitory
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What is drug resistance due to?
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it is due to the genetic versatility and adaptibility of microbial populations
-transformation, transduction, conjugation -phenotypic change |
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How does drug resistance develop?
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microbes become newly resistant to a drug after one of the following occurs: spontaneous mutations in critical genes; acquisition of entire new gene or set of genes via horizontal transfer from another species
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What are resistance factors?
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plasmids (small circular part of DNA) containing antibiotic resistance genes
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How can resistance factors be transferred?
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through conjugation, transformation or transduction; transposons- "jumping genes"
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What are the 5 mechanisms of drug resistance?
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new enzymes inactivates drug; permeability of drug is decreased; drug is immediately eliminated; drug binding sites changes; an affected metabolic pathway is shut down or an alternative is used
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What are the long-term therapeutic consequences?
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population-one is resistant
bacteria in an infection-take all antibiotics prescribed: kills vulnerable cells, non resistant cells; makes a resistant population |
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What are the events in natural selection for drug resistance?
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sensitive cells die, resistance mutant cells survive and all cells are now resistant
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What are the 4 new approaches to antimicrobial therapy?
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1. targeting iron-scavenging capabilities of bacteria
2. using RNA interference strategies- to shut down metabolism of pathogenic microbes 3. mimicking defense peptide molecules- peptides of 20-50 amino acids, part of the mammalian innate immune system called defensin, magainins, and protegrins 4. using bacteriophages: they are specific-infect only one species of bacterium |
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What are probiotics?
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can replace microbes lost during antimicrobial therapy
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What are prebiotics?
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nutrients that encourage the growth of beneficial microbes
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What are side effects of drugs?
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-direct damage to tissues
-allergic reactions -disruption to normal biota |
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What organs can drugs adversely affect?
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liver, kidneys, GI tract, cardiovascular system and blood forming tissue, nervous system, respiratory tract, skin, bones and teeth
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What is an allergy?
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an increased sensitivity to a drug
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What does a drug act in a allergic response?
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drugs act as an antigen that stimulates the allergic response
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When does sensitization occur?
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during the second exposure it can lead to hives, respiratory inflammation or anaphylaxis
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What is biota?
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normal microbial colonists of healthy body surfaces
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What antimicrobials can destroy healthy biota?
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broad spectrum- this can lead to a superinfection
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What is a superinfection?
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microbes that were once small in number overgrow when normal resident biota are destroyed by broad-spectrum antimicrobials
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What is the role of antimicrobials in disrupting microbial biota and causing superinfections?
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Normal biota important to maintain intestinal balance; drug destroys beneficial biota; pathogen overgrows
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