antimicrobials

Question 1

Why would a bacteriostatic agent be used?

Answer 1

if you can stop growth, immune system can take over

-not a good option in immunosuppressed patients

Question 2

post antibiotic effect

Answer 2

inhibition does cont fairly long time after a drug is d/c’d

• persistent suppression of microbial growth after antimicrobial agent has been cleared
• Long PAE with intracellular bacteriostatic agents, short or no PAE with beta-lactams
• might make length of dosing interval versus the the drug half life less of a concern

Question 3

MBC vs MIC

Answer 3

MBC = minimal bactericidal concentration
MIC = minimal inhibitory concentration

antibiotic in the blood should exceed the MIC by 2-8x to offset tissue barriers to infection site (pus, CNS, tissue)

Question 4

Which mechanisms of action are bacteriostatic

Answer 4

folic acid metabolism inhibition, PRO synthesis inhibition

Question 5

concentration dependent antibiotics

Answer 5

antibiotic effectiveness is dependent on achieving peak concentration periodically in multiple dosing regiment Peak/MIC or AUC/MIC
-common for bactericidal agents to show concentration dependent technology

Question 6

time dependent antibiotics

Answer 6

effectiveness dependent on time (%) that concentration remains above MIC (time > MIC)

• common for drugs like cell wall synthesis inhibitors, slow killing req maintained concentrations
• ex: PCN
• requires minimization of dosing interval relative to drug t1/2 or IV infusion

Question 7

narrow spectrum antibiotics

Answer 7

• effectively mainly against either Gm+ or Gm-
• optimal against specific organisms
• lower risk of superinfections

Question 8

extended spectrum antibiotics

Answer 8

-affects a variety of Gm+ and Gm-

Question 9

broad spectrum

Answer 9

affects both Gm+ and Gm - bacterial, plus other micororg as well (rickettsia

Question 10

clinical effectiveness of antibiotics

Answer 10

dependent on drug’s maximal efficacy (limit of the dose-response relation), not its potency

Question 11

what contributes to antimicrobial drug resistance

Answer 11

• misdiagnosis
• inherent microbial resistance (certain strains)
• acquired drug resistance

Question 12

Forms of acquired microbial resistance

Answer 12

• drug fails to reach target (transporters)
• drug is inactivated (enzymes, pumped out of cells by efflux pump)
• drug target is altered (rapid multiplication leads to rapid mutation)

-occurs as a result of antibiotic use

Question 13

how is drug resistance acquired genetically?

Answer 13

• chromosomal resistance (mutant genes and PRO, drug target is altered)
• sex, plasmid, and transposon mediated resistance
• conjugation (imp for gram neg)
• transduction (imp)
• transformation (not imp)

Question 14

non-genetic drug resistance

Answer 14

• growth latency, anaerobic conditions

- protoplasts (no cell wall)

Question 15

definitive antimicrobial therapy

Answer 15

• identificaiton of specific pathogen prior to rx
• presumptive dx of infection, severity/need for immediate rx, and probable pathogens
• formulate a microbial dx
• direct examination, gram stain, etc.; growht & sensitivity tests
• select most appropriate antibiotic therapy
• evaulate effectiveness (72h) and reassess

Question 16

empiric antimicrobial rx

Answer 16

-rx without formal id of specific pathogen
-used in critical conditions or when dx is likely to be unneccessary or cost prohibitive
-presumptive dx of infection, severity/need for rx, and probable pathogens
-rx with antimicrobial agents likely to be effective
(consider local bacterial resistance patterns, generally involves broader spetrum agents, isolation of cultures prior to antimicrobial rx, eval effectiveness and reassess)

Question 17

adverse effects of antimicrobial therapy

Answer 17

• allergy
• superinfection (appearance of a secondary infection during antimicrobial rx of a primary infection)
• organ tox
• selection of resistant microbes

Question 18

valid indications for combination antimicrobial therapy

Answer 18

• empirical therapy of severe infection of unknown cause
• rx of polymicrobial infections
• enhancement of antibacterial activity in the treatment of specific infections
• preventing the emergence of resistant microbes

Question 19

disadvantages of combination antimicrobial therapy

Answer 19

• synergistic toxicity (one agent enhances toxicity of the other)
• cost
• antagonism
• selection for drug resistant bugs

Question 20

prophylaxis of antimicrobial therapy

Answer 20

• pre-surgery patients with indwelling medical devices
• prevent wound infection following surgery (oral, GU, bowel)
• sexual contacts of patients with STDs
• dental procedures in patients with indwelling medical devices, heart defects (recommendations have changed)