Flashcards in topic 8 Deck (19):
What is the definition of a chemotherapeutic agent?
1. Chemotherapeutic Agent
Original definition by Paul Ehrlich was to the effect that “a chemical that inhibits the growth of microorganism without harming the human host.”
Currently, however, the term is used as “any chemical that is used for treating any disease.”
What is the definition of an antiobiotic?
Antimicrobial agents are natural or synthetic chemical substances that suppress the growth of, or destroy, microorganisms such as bacteria, fungi and viruses.
What are 5 characteristics of an ideal antibiotic?
1. Bactericidal rather than bacteriostatic
2. High margin of safety
3. Stable and active in all types of milieu
4. No hypersensitivity reactions
5. Reasonable cost.
What are 3 classifications of chemotherapeutic drugs? What are 3 subclassifications of antimicrobial drugs? How are antimicrobial drugs classified?
Antimicrobial (Antibacterial, antifungal, antiviral)- classified based on site and mechanism of action
Antiparasitic (amoeba, helminths)
What is the importance of the host response?
The immune system of the host is essential for getting rid of an infection and produces signs and symptoms of the illness. It must be considered when designing and giving drugs.
What are two dimensions on the antimicrobial spectrum? What does each mean?
cidal or static-bactericidal drugs actually kill the microorganism, bacteriostatic drugs stop the microbe from growing and require the immune system to do the rest (cidal is preferred).
Narrow or broad-Broad spectrum drugs target many different kinds of organisms. Narrow spectrum target specific kinds of microorganisms (preferred if you know the microbe that is causing the illness b/c broad ones can kill normal flora as well, open body for further infection).
What is the MIC, MBC, and PAE?
MIC (minimum inhibitory concentration)-minimum conc. or drug required to inhibit bacterial growth
MBC (minimum bacterial concentration)-Minimum conc. of drug required to start killing bacteria.
PAE (post anti-biotic effects)-Even after an antimicrobial is washed out, growth might not occur for awhile. Depends on drug.
What are 7 drug factors that influence which antibiotic to use?
• Activity against the pathogen
• Ability to reach the site of infection
• Available route of administration
• Adverse effect profile
• Dosing Schedules
• Taste (for suspensions)
Why must antibacterial concentrations exceed MIC? What must be done to combat this?
Most drugs will not be found directly in blood, so the drug must be distributed. Some sites have a similar serum concentration, but some will be protected more or less (eye, prostate, etc.). High parentral doses are required to combat this.
What are 5 host factors that influence which antibiotic to use?
• Site of Infection
• Renal and Hepatic Function
• Drug allergies
• Required route of administration
What are 2 ways in which bacteria can become resistant to multiple drugs?
They can acquire multiple, unrelated resistance genes which requires many steps.
They can acquire one resistance gene that works against multiple drugs which requires a single step.
Some bacteria have been found that are resistant to all know antibacterial agents.
What are 3 general mechanisms of drug resistance?
Inactivation of drug by microbial enzymes
Decreased accumulation of drug by microbe
Reduced affinity of the target macromolecule for the drug.
What are 3 possible effects of combination therapy? What is an example of how synergy could work?
Synergy-two drugs work even better than if you added the effects of both working alone.
Indifference-Two drugs together don't work any better than one of them alone.
Antagonistic-Two drugs together work worse than one of them does alone.
Aminoglycose inhibits protein synthesis intracellularly. It may be limited some by not being able to enter the bacteria well enough. Penicillin kills by preventing formation of the cell wall, which will kill some bacteria. Together, the penicillin opens the cell wall which allows the aminoglycose to get inside the cell and inhibit cell growht which works great.
When is single drug therapy the best idea? Why?
When the infecting bacteria has been identified b/c
Killing of normal flora is minimized
Toxicity of the drug is minimized
Why is combination therapy sometimes warranted?
It decreases the likelihood of the emergence of resistant strains b/c
A single agent might not work against a resistant strain and thus it will simply select it out. Adding a second agent might kill the mutated strain.
Also, it is often advantageous to use two drugs if they're synergistic.
What are some guidelines for appropriate use of antibiotics?
Before bacterial identification: can use combo or single agent.
After identification: try to use a low toxicity narrow spectrum drug based on the drug's selectivity for the most likely bacterial culprit.
Also, don't use an antibacteria unless the culture indicates it b/c they can be toxic and result in resistant bacterial strains when used too much.
What are some inappropriate/unethical uses of antibiotics
Treatment of untreatable infections (viral infections, b/c the patient has a fever of unknown origen (often viral), measles/mumps/90% of upper respiratory infections)
Improper dosage (some drugs are given at subtherapeutic dosages to avoid toxicity. This results in selection of resistant bacteria).
Inappropriate dependence on chemotherapy alone (sometimes surgery is required to remove abscesses, drain pus, etc. b/c w/o it, the drug won't work.
Lack of adequate bacteriological info (you should get tests and you should give an antibiotic appropriate for the specific case, not the same one every time).
What are some untoward effects of antibiotics?
RXNs due to toxic properties
hypersensitivity reactions (allergies)
superinfections (more resistant bacteria take over for the ones that were killed)