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Week 11 - Antibiotics for Surgical Procedures Flashcards

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1
Q

Where do 80% of nosocomial infections occur?

A

Urinary tract – foley catheters

Respiratory system – ventilators and VAP

Bloodstream – IV catheters

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2
Q

What are the patient related risk factors for surgical site infections?

A
  • Age extremes <5 or >65
  • Poor nutritional status
  • Diabetes mellitus AND periop glycemic control (<200)
  • Peripheral vascular disease
  • Tobacco use (quit 4-8 weeks preop reduces SSI 50%)
  • Coexisting infections
  • Altered immune response
  • Corticosteroid therapy
  • Preoperative skin preparation (scrub and shave)
  • Preoperative length of stay (longer preop stay greater risk of infection)
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3
Q

What are the facility related risk factors for surgical site infections?

A
  • Experience of surgeon (volume-outcome relationship)
  • Technique (Open vs laparoscopic procedure)
  • Length of surgery
  • Type and method of sterilization of instruments
  • Perioperative normothermia
  • Appropriate antibiotic dosing and re-dosing as needed
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4
Q

What is the ideal antimicrobial agent?

A

Acts on the pathogen and not the host

Does this via:

  • Unique cellular structures and biochemical pathways
  • Common pathways but altered affinities for certain components
  • Prodrugs that are converted by only the pathogen
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5
Q

What does mismanagement of prophylactic antibiotics lead to?

A
  • Increased risk of surgical site infection and hospital acquired infections
  • Increased surgical morbidity and mortality
  • Increased cost
  • Associated with the rise in resistant infections nationwide

*inappropriate use continues to be a major problem for surgical patients

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6
Q

What are the risk factors for microbial resistance?

A

Antibiotics (2nd largest class of prescribed medications)

Extended/inappropriate use of antibiotics

Transmission of infection

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7
Q

What are the different antimicrobial spectrums of activity?

A

Narrow Spectrum: effective against Gm+ OR Gm- microbes

  • works well for specific organisms and most surgical prophylaxis
  • lowers risk of developing superinfections

Extended Spectrum: affects Gm+ AND Gm- bacteria

Broad Spectrum: affects Gm+ AND Gm- bacteria AND other microorganisms

  • greater risk of superinfections
  • don’t typically give in OR
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8
Q

What are the common narrow spectrum antimicrobial agents?

A 
Clindamycin*
Vancomycin*
Bacitracin
Macrolides
Metronidazole
PCN G
PCN V
Polymyxins
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9
Q

What are the common extended spectrum antimicrobial agents?

A 
Cephalosporins*
Aminoglycosides
Extended PCNs
Fluoroquinolones
Imipenem
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10
Q

What are the common broad spectrum antimicrobial agents?

A

Chloramphenicol
Sulfonamides
Tetracyclines
Trimethoprim

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11
Q

Bactericidal vs Bacteriostatic

A

Bactericidal = agents KILL the microbes (killing infection that occurs requires bactericidal)
*MBC - minimal bactericidal concentration

Bacteriostatic = agents INHIBIT GROWTH of microbes (surgical prophylaxis requires bacteriostatic)
*MIC - minimal inhibitory concentration – surgical dosing

  • Type of microbe is important
  • Chosen antimicrobial’s spectrum of activity is important
  • Antimicrobial level in the blood should exceed the MIC by 2-8x to provide prophylaxis against infection
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12
Q

What common antimicrobial agents are bactericidal?

A 
Aminoglycosides
Bacitracin*
Daptomycin
Fluoroquinolones
Imipenem*
Isoniazid
Metronidazole
Penicillins*
Cephalosporins*
Polymyxins
Rifampin
Vancomycin*
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13
Q

What common antimicrobial agents are bacteriostatic?

A 
Clindamycin*
Erythromycin
Nitrofurantoin
Sulfonamides
Tetracyclines
Trimethoprim
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14
Q

When is Chlorhexidine skin prep bactericidal and when is it bateriostatic?

A

Bacteriostatic = low concentrations

Bactericidal = high concentrations

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15
Q

What percent of iodine based skin prep is bactericidal?

A

Broad spectrum bactericidal at 1%

*higher concentrations cause necrosis

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16
Q

What are the common antibiotics mechanism of actions?

A

Cell Wall Synthesis:

  • Beta Lactams (popular surgical prophylaxis): PCN, Cephalosporins, Carbapenems, Monobactams
  • Vancomycin, Bacitracin
  • Cell Membrane: Polymyxins

Nucleic Acid Synthesis:

  • Folate synthesis (sulfonamides, trimethoprim)
  • DNA Gyrase (quinolones)
  • RNA Polymerase (rifampin)

Protein Synthesis:

  • 30S Subunit (tetracyclines, aminoglycosides)
  • 50S Subunit (macrolides, clindamycin, linezolid, chloramphenicol, streptogramins)
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17
Q

What are beta-lactam antibiotics?

A

Broad spectrum antibiotics that contain a beta-lactam ring in the structure

–Penicillins – Cephalosporins – Monobactams – Carbapenems –

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18
Q

What are the different Penicillins?

A

Derived from Penicillium fungi

PCN-G = IV form — PCN-G = PCN-G-K (K is for potassium – beware high doses)

PCN-V = PO form

  • there is an IM form
  • allergic to one PCN – allergic to all PCN
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19
Q

When are Penicillins the drug of choice?

A
  • Pneumococcal infections
  • Streptococcal infections
  • Meningococcal infections
  • Highly effective treatment for syphilis
  • Actinomycosis and clostridial infections that result in gas gangrene
  • Prophylactic for patients with history of rheumatic fever and surgery or dental work to treat transient bacteremia
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20
Q

How are PCNs excreted?

A

Renal excretion = Rapid (60-90% of an IM dose is excreted within 1 hour) – plasma concentration decreases to 50% its peak within 1 hour

10% GFR
90% renal tubular secretion

  • if renal failure, need to adjust dose
  • anuria increases elimination T1/2 of PCN-G by 10x
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21
Q

What are Cephalosporins (Gen 1-3) active against?

Study These Flashcards
A

First generation = mostly active against Gram+ bacteria

Successive generations = more active against Gram-

*increasing affinity for Gm- resulted in decreased affinity for Gm+

22
Q

What are Cephalosporins mechanism of action?

Study These Flashcards
A

Bactericidal via interruption of cell wall synthesis
-more resistant to Beta-Lactamases

Disrupt B-Lactam ring and inhibit activity

~5-10% (rare) may have cross-reactivity with PCNs and/or Carbapenems (lack of suitable alternatives has forced use of Cephalosporins in these pts)

  • allergic reactions in 1-10% of patients
  • cross reactivity between Cephalosporins (all-for-one)
23
Q

What is PCN resistance due to?

Study These Flashcards
A

Bacterial production of Beta-lactamase enzymes that hydrolyze the Beta-lactam ring, rendering the antimicrobial inactive

*Methicillin, Oxacillin, Nafcillin, Cloxacillin, and Dicloxacillin are not hydrolysis susceptible to hydrolysis and will frequently work against these organisms – these drugs are used in infections caused by staphylococci

24
Q

What is resistance to Cephalosporins due to?

Study These Flashcards
A

Inability to penetrate the site of action

25
What is an example of a first generation cephalosporin? How is it administered? How is it excreted?
Cefazolin Poor PO -- reasonable IM absorption and well tolerated -- IV is best 1st Gen excreted largely unaltered by the kidneys -decrease dose in renal failure
26
What is an example of a second generation cephalosporin?
Cefoxitin and Cefuroxime - Extended activity against Gm- bacteria - Shorter T1/2 - Excreted unchanged by the kidney *Cefuroxime is only 2nd gen good for treating meningitis
27
What is an example of a third generation cephalosporin?
Cefotaxime - resist beta-lactam hydrolysis - achieves CSF levels and good for meningitis - Elimination T1/2 one hour requiring more frequent redosing
28
What are Monobactams (Axtreonam) effective against?
Effective ONLY against Gram- bacteria (Neisseria, Pseudomonas) Resistant to some beta-lactamases *not absorbed PO -- must be given IM or IV
29
What are Carbapenems useful for?
Imipenem, Meropenem, Ertapenem, Doripenem Useful for multi-drug resistant infections (hospitalized pts) * Broader spectrum than other beta-lactams * Less affected by mechanisms of antibiotic resistance
30
What can Clindamycin cause?
Pseudomembranous Colitis - reserved for severe infections not controlled by other less toxic antibiotics - d/c if significant diarrhea
31
What effect can high doses of Clindamycin have at the NMJ?
Produces pre- and post-junctional effects at NMJ *these effects cannot be readily antagonized with calcium or AChE drugs High doses can result in profound and long-lasting neuromuscular blockade in the absence of nondepolarizing muscle relaxants
32
What is vancomycin?
Bactericidal glycopeptide that impairs cell wall synthesis of Gram+ bacteria - works well PO for enterocolitis because it's poorly absorbed from the GI tract - Drug of choice for MRSA infections IV 10-15mg/kg -- MUST be given slowly over 60 minutes *sustained plasma concentration for 12 hours - rarely re-dose in OR
33
What does a fast administration of vancomycin result in?
A large histamine release - Red Man's syndrome - Severe hypotension - Cardiac arrest?
34
What are Fluoroquinolones good for?
Ciprofloxacin is highly effective for urinary and genital tract infections (prostatitis and GI infections) Upper and lower respiratory infections Soft tissue, bone, and joint infections *high blood levels and good tissue penetration make it a good antibiotic
35
What is the mechanism of action of chlorhexidine?
Disrupts cell membranes of bacteria Effective against G- and G+ * persists on skin to provide continuous coverage * 2% is more effective than povidine-iodine as hand scrub
36
How quickly does iodine act?
Rapid acting antiseptic that, IN THE ABSENCE of, organic material kills bacteria, viruses, and spores 1% iodine kills 90% bacteria in 90 seconds 5% iodine kills 90% bacteria in 60 seconds >7% iodine may cause cutaneous burns ***MUST DRY to be effective
37
What do you need to be aware of/check for with surgical antibiotic prophylaxis?
- Ensure surgical antimicrobial orders reflect published evidence - Achieve plasma concentration prior to incision - Infusion must be completed prior to tourniquet inflation - Maintain intra-op MIC plasma concentration until skin closure*** - Interval dosing based on the particular antibiotic administered - Additional dose anytime EBL exceeds 1500 mL since last dose
38
What is the most commonly used antibiotic for surgical prophylaxis?
Cefazolin (1st gen cephalosporin) *wide therapeutic index and low incidence of side effects, cost effective
39
What antibiotics are typical backups for B-lactam allergy?
Clindamycin Vancomycin Gentamicin
40
What are antibiotic re-dosing intervals based on?
2-2.5 times the T1/2 in the general population with normal renal function *doses are based on ideal body weight
41
What perioperative antibiotics need to be re-dosed every 2 hours?
Ampicillin-sulbactam Ampicillin Cefoxitin Piperacillin-tazobactam
42
What perioperative antibiotics need to be re-dosed every 3 hours?
Cefotaxime
43
What perioperative antibiotics need to be re-dosed every 4 hours?
Aztreonam Cefazolin Cefuroxime
44
What perioperative antibiotics need to be re-dosed every 6 hours?
Cefotetan Clindamycin
45
What are the four main factors for surgical site infections?
- Host Fitness (ability to the host to defend) - Inoculum (amount of pathogen transmitted) - Wound Microenvironment (conditions at the wound site) -- necrotic tissue, stitches, the inoculum itself - Pathogen Virulence (ability of the pathogen to cause disease)
46
What is the most common causes of bacteremia or fungemia in hospitalized patients?
IV access catheters *S. aureus and S. epidermidis
47
What is the mechanism of action of Penicillins?
Bactericidal -- Cell Wall Synthesis Inhibitors - Interfere with the synthesis of peptidoglycan -- essential component of cell walls of susceptible bacteria - Decrease the availability of an inhibitor of murein hydrolase such that the uninhibited enzyme can then destroy (lyse) the structural integrity of bacterial cell walls * resistant Gm- bacteria prevent access to sites where synthesis of peptidoglycan is taking place
48
What are the broad-spectrum penicillins?
2nd Gen PCNs: Ampicillin, Amoxicillin (broad spectrum) 3rd Gen PCNs: Carbenicillin (extended spectrum) 4th Gen PCNs: Mezlocillin, Piperacillin, Azlocillin (extended - broadest spectrum) - wider range of activity than other PCNs -- bactericidal against Gm- and Gm+ bacteria * inactivated by penicillinase produced by certain bacteria -- not effective against most staphylococcal infections
49
What are Clavulanic acid, Sulbactam, and Tazobactam?
Beta-lactam compounds that bind irreversibly to the Beta-lactamase enzymes *inactivate Beta-lactamase enzymes causing the bacteria to be sensitive to PCNs
50
What are Erythromycin or Clindamycin an effective alternative for?
Treatment of streptococcal pharyngitis, bronchitis, and pneumonia in patients who can't tolerate PCNs or Cephalosporins *Erythromycin prolongs QT -- torsades de pointes
51
What are Bacitracins?
a group of polypeptide antibiotics effective against a variety of Gm+ bacteria * use limited to topical application - treat furunculosis, carbuncle, impetigo, suppurative conjunctivitis, and infected corneal ulcer

Anesthesia Pharm (18 decks)

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