Antibiotics Overview- Quiz 2

Question 1

Bacteriocidal vs Bacterostatic antibiotics

Answer 1

Bacteriostatic: arrest growth
and replication of bacteria
at drug levels achieved (While many of these agents can effectively eliminate pathogens, they do not meet the predefined threshold in bacterial classification)

Bacteriocidal: Able to effectively kill
>/=99% within 18-24° of incubation

-NOTE* Its possible for a drug to be one kind to one microbe and another to a different microbe

Question 2

MIC—Minimal Inhibitory Concentration vs.
MBC—Minimum Bactericidal Concentration

Answer 2

MIC:
Lowest antimicrobial concentration that prevents visible growth of a microbe after 24° of incubation
-Quantitative measure of in vitro susceptibility
-MIC is most common approach used by clinical labs
MORE IMPORTANT

MBC:
-Lowest concentration of antimicrobial agent that
results in a 99.9% decline in colony count after overnight broth dilution incubations
-MBC rarely determined in practice

Question 3

What are some natural barriers to drug delivery?

Answer 3

-Prostate, testicles, placenta, vitreous, CNS

-Particularly important—blood-brain
barrier—prevent entry from the blood to the brain of virtually all molecules, except those that are small and lipophilic (if meninges/ BBB
are inflamed MAY be able to get less lipophilic meds thru as permeability is increased)

NOTE* LOW molecular weight, LOW protein binding ability also pass more easily thru the BBB, and affinity for transporters or no affinity for efflux pumps also get drugs to better penetrate the BBB*

Question 4

What patient factors affect the selection of antimicrobials?

Answer 4

1. Their immune system (ETOH, pregnancy, age, autoimmunity)

2.Renal dysfunction (can be preferable to monitor direct DRUG levels to prevent toxicity than going by Cr i.e. vanco)

3. Hepatic dysfunction
4. Poor perfusion
5. Age (old or young)
6. Pregnancy and lactation

Question 5

Risk factors for MDRO

Answer 5

-Prior use of antibiotics in last 90 days
-Hospitalization for >2 days within last 90 days
-Current hospitalization exceeding 5 days
-Admission from a NH
-High frequency of resistance in the
community or local hospital [using
hospital antibiograms]
-Immunosuppressive disease and/or
therapies

(Need broader antibiotic coverage)

Question 6

Which antibiotics are notably the least toxic?

Answer 6

-Penicillins

-Among least toxic of ALL
antibiotics because they interfere
with a site or function unique to the
growth of the bacteria

Question 7

Concentration dependent killing

Answer 7

-Refers to the antimicrobial property where the effectiveness of bacterial eradication increases with higher drug concentrations

-Giving drugs that exhibit this concentration-killing by a once a day bolus infusion obtains high peak levels that cause rapid killing of the bug

-Thus, dosing strategies often involve higher doses with extended intervals to maximize bacterial kill while minimizing toxicity.

Question 8

Time-Dependent [Concentration-Independent] Killing

Answer 8

-Refers to the antimicrobial property where bacterial eradication is primarily dependent on the duration the drug concentration remains above the minimum inhibitory concentration (MIC), rather than peak concentration.

-Dosing strategies focus on frequent dosing or continuous infusions to maintain effective drug levels.

Question 9

Postantibiotic Effect [PAE]

Answer 9

-Refers to the continued suppression of bacterial growth even after antibiotic levels drop below the minimum inhibitory concentration (MIC).

-Drugs that have a PAE often require one dose per day.

Question 10

Chemotherapeutic Spectra

Answer 10

Narrow: acts on a single/ limited group of microbes (Isoniazid)

Extended Spectrum: are modified to be effective against gram +
organisms and also against
a number of gram –bacteria

Broad spectrum: Drugs affect a wide variety of microbe species
-These drugs can alter the nature of the normal bacterial flora and lead to
superinfection from pathogens

Question 11

Advantages vs. Disadvantages of combining antibiotics together

Answer 11

Advantages:
-Some combinations show
synergy (although this is rare and used for things like enterococcal endocarditis)
-Combinations often used when infection is of unknown etiology or several organisms with variable sensitivities— such as TB

Disadvantages:
-Many drugs work only when
pathogens are multiplying, so when
combos are given where one is
bactericidal and other is
bacteriostatic—the 1st drug may
interfere with the action of the 2nd
agent
-Another concern is development of
resistance from giving unneeded
combinations

Question 12

Genetic Alterations Leading to Drug Resistance

Answer 12

-Acquired antibiotic resistance requires the temporary or permanent gain or alteration of
bacterial genetic information

-Resistance occurs due to the ability of DNA to change/mutate or to move from one organism to another

Question 13

When would you use preventative antibiotics?

Answer 13

-Usually only for dental procedures

Question 14

Main ADE’s of antibiotics

Answer 14

1. Hypersensitivity reactions
   (Red man syndrome from rapid infusion of vancomycin)
   -Patients with history of Stevens-Johnson syndrome/ Toxic Epidermal Necrosis from an antibiotic should
   NEVER be rechallenged
   -Penicillins can cause urticaria, anaphylactic shock

2.Direct toxicity (High serum drug levels can cause toxicity by directly
affecting cellular processes in the patient)
-Aminoglycosides can cause ototoxicity
-Chloramphenicol can cause bone marrow suppression
-Fluoroquinolones can have effects on cartilage and tendons
-Tetracyclines can directly affect bones
-Many antibiotics can cause photosensitivity

3. Superinfections

Question 15

How are antimicrobials classified?

Answer 15

1. Chemical structure
2. Mechanism of action
3. Activity against particular types
   of pathogens