ICL 2.26: Intro to Antibiotics Flashcards
what are antimicrobial drugs?
they’re chemicals used to treat microbial infections
before antimicrobials, large number of people died from common illnesses
now many illnesses are easily treated with antimicrobials
what are the characteristics of an ideal antibiotic?
- broad-spectrum
- favorable pharmacokinetics = reach target site in body with effective concentration
- preserve normal microbial flora
- does not induce resistance
- selective toxicity -low side effects
what is selective toxicity?
cause greater harm to microorganisms than to host
so it’s the balance between efficacy and toxicity
what is the chemotherapeutic index?
lowest dose toxic to patient divided by dose typically used for therapy
chemotherapeutic index = toxic dose/therapeutic dose
what does bacteriostatic mean?
inhibit growth of microorganisms
static antibiotics allow the immune system the time to eliminate the infecting agent
what does bactericidal mean?
kills microorganisms
what patient population can’t be treated with static antibiotics?
- immunodeficient patients with acute infections
2. patients with infections in immunologically privileged sites
what is the spectrum of activity of an antibiotic drug?
antimicrobial medications vary with respect to the range of microorganisms they kill or inhibit
- narrow-spectrum antimicrobials = kill only limited range
- broad-spectrum antimicrobials = kill wide range of microorganisms
what is the tube dilution method of the susceptibility test?
Minimum inhibitory concentration (MIC) = lowest concentration of antibiotic that inhibits visible growth
Minimum bactericidal concentration (MBC) = lowest concentration of antibiotic that kills 99.9% of the inoculum
what is the disk diffusion method of the susceptibility test?
Zone of inhibition (ZOI) = the correlation of ZOI and MIC has been established by FDA
MIC = lowest concentration of antibiotic that inhibits visible growth
what are the different mechanisms of action of antibacterial drugs?
- inhibit cell wall synthesis
- inhibit protein synthesis
- inhibit nucleic acid synthesis
- injury to plasma membrane
- inhibit synthesis of essential metabolites
which antibiotics inhibit cell wall synthesis?
- penicillins
- cephalosporins
- vancomycin
what does polymyxin B do?
binds to membrane of gram (-) bacteria and alters permeability
this leads to leakage of cellular contents and cell death
these drugs also bind to eukaryotic cells to some extent, which limits their use to topical applications
which antibiotics inhibit nucleic acid synthesis?
- fluoroquinolones
2. rifampin
what do fluoroquinolones do?
antibiotic that inhibits nucleic acid synthesis
it inhibits enzymes that maintain the supercoiling of closed circular DNA
what does rifampin do?
antibiotic that inhibits nucleic acid synthesis
it blocks prokaryotic RNA polymerase from initiating transcription
how do antibiotics that inhibit synthesis of metabolites work?
competitive inhibition by substance that resembles normal substrate of enzyme
ex. sulfa drugs
how do antibiotics that inhibit protein synthesis work?
they target the ribosomes of bacteria
which antibiotics inhibit protein synthesis?
- tetracyclines
- chloramphenicol
- aminoglycosides
what do tetracyclines do?
they inhibit protein synthesis by binding to 30S subunit of bacterial ribosomes and blocking attachment of tRNA
what does chloramphenicol do?
it inhibits protein synthesis by binding to 50S subunit and prevents continuation of protein synthesis
what do aminoglycosides do?
they inhibit protein synthesis by binding to 30S subunit causing it to distort and malfunction; blocks initiation of translation
what is synergism?
combining drugs that work together
antibiotic combination is four or more times as great as the sum of their individual effects
how do penicillin + aminoglycoside create synergism?
aminoglycosides do not get across the cell wall very good
but penicillin weakens the cell wall barrier and allows better penetration
this allows small amounts of the relatively toxic aminoglycoside to be used
what are antagonistic effects?
drug combinations that work against each other
how are penicillin and chloramphenicol antagonistic?
penicillin inhibits cell wall synthesis which requires rapidly growing bacteria
chloramphenicol on the otherhand is bacteriostatic so it stops the multiplication and stops the need for cell wall synthesis
this makes penicillin irrelevant…
what is the benefit of multiple-drug therapy?
- prevents the onset of disease in immunosuppressed or debilitated patients
- empirical therapy when the specific agent of disease is unknown
- treat infections that involve more than one bacterial species
- treat infections caused by bacteria that are difficult to eradicate
- to treat chronic diseases in which bacteria may develop resistance to an antibiotic during the course of therapy
what is natural vs. acquired resistance?
natural resistance = structural barrier, transport system, lack of target
acquired resistance = mutation, gene exhange etc.
what are some instances of overuse/misuse of antibiotics?
- Prophylactic use before surgery
- Empirical use (blinded use)
- Increased use of broad spectrum agent
- Pediatric use for viral infections
- Patients who do not complete the course (chronic disease, eg. TB, AIDS)
- Antibiotics in animal feeds
what’s the problem with overuse/misuse of antibiotics?
bacterial resistance!!
what is the clinical significance of antibiotic resistance?
- therapeutic failures and relapse
- facilitates spread in the hospital under “antibiotic pressure”
- eed to use more costly and toxic agents
- the emergence of untreatable pathogens
