Infectious Disease Antibiotics Ch. 22 Naplex 2026

How to select an empiric abx

1) Based on inf site and likely organisms

2) Inf severity: community vs hospital-acquired

3) Spectrum of activity, local antibiogram

4) Ability to penetrate site of inf

5) Side effects

6) Pt age, weight, allergies, renal or hepatic fxn, comorbidities, recent abx use, colonization

7) Guidelines: IDSA and CDC

What is an antibiogram

a list of bacteria and the antibiotic sensitivities at a specific hospital

Thick cell wall

Gram stain: Stains dark purple or blue from the crystal violet stain

A) gram-pos organism

B) gram-neg organism

C) atypical organism

A) gram-pos organism

Thin cell wall

Gram stain: Takes up safranin counterstain, resulting in pink color

A) gram-pos organism

B) gram-neg organism

C) atypical organism

B) gram-neg organism

Has no cell wall

Does not stain well in a gram stain

A) gram-pos organism

B) gram-neg organism

C) atypical organism

C) atypical organism

What microbes stain gram-positive (purple) as cocci clusters?

Staphylococcus spp. such as MSSA and MRSA

Staphylococcus epidermidis

What microbes stain gram-positive (purple) as cocci pairs and chains?

Streptococcus pneumoniae (diplococci)

Streptococcus spp such as Streptococcus pyogenes

Enterococcus species including VRE (Vancomycin resistant enterococcus)

What microbes stain gram-positive (purple) as rods/bacilli?

Listeria monocytogenes

Corynebacterium spp

What microbes stain gram-positive (purple) as spores?

Peptrostreptococcus

Propionibacterium acnes

Clostridiodes difficile

Clostridium spp

What microbes don't gram stain well?

Mycobacterium tuberculosis

Atypicals:

Chlamydophila

Legionella

Mycoplasma

What microbes stain gram-negative (red) as cocci?

Neisseria spp

What microbes stain gram-negative (red) as coccobacilli?

Acinetobacter baumannii

Bordatella pertussis

Moraxella catarrhalis

What microbes stain gram-negative (red) as rods?

And they colonize the gut , "enteric"?

Proteus mirabilis

Escherichia coli

Klebsiella spp

Serratia spp

Enterobacter cloacae

Citrobacter spp

What microbes stain gram-negative (red) as rods?

And they do not colonize the gut?

Pseudomonas aeruginosa

Haemophilus influenzae

Providencia spp.

What microbes stain gram-negative (red) as curved or spiral-shaped rods (spirochete)?

Helicobacter pylori (H. pylori)

Campylobacter spp

Treponema spp

Borrelia spp

Leptospira spp

What microbes stain gram-negative (red) and are anaerobes?

Bacteroides fragilis

Prevotella spp

What is a coagulase test?

What organisms are coagulase positive?

A test to differentiate between the Staphylococcus species

Coagulase-positive: Staph aureus (MSSA or MRSA)

What is the minimum inhibitory concentration (MIC)?

The min conc of each abx that inhibits bacterial growth

Provides an interpretation of susceptible/resistant/intermediate for a susceptibility report

What is "intrinsic" antibiotic resistance?

Microbial resistance to the drug is natural

eg) E. coli is resistant to vancomycin bc this antibiotic is too large to penetrate the cell wall of E. coli

What is "selection pressure" antibiotic resistance?

Resistance that occurs when abx kill susceptible bacteria, leaving behind more resistant strains to multiply

eg) Vancomycin used in a patient then created VRE in the gut

What is "acquired" antibiotic resistance?

Bacterial DNA containing resistant genes can be transferred b/w species and/or picked up from dead bacterial fragments in the environment

Name some examples of antibiotic degradation thru bacterial enzymes

1) Beta-lactamases

2) Extended-spectrum beta-lactamases (ESBL)

3) Carbapenem-resistant Enterobacterales (CRE)

List the common resistant pathogens?

Use the mneumonic

Kill Each And Every Strong Pathogen

K = Klebsiella pneumoniae (ESBL, CRE)

E = Escherichia coli (ESBL, CRE)

A = Acinetobacter baumannii

E = Enterococcus faecalis, Enterococcus faecium (VRE)

S = Staphylococcus aureus (MRSA)

P = Pseudomonas aeruginosa

When an antibiotic kills GI flora, it can result in an overgrowth of (what microbe) which can lead to an infection?

Clostridoides difficile

Leading to C. diff infection

All antibiotics have a risk for ____ infection but the highest risk is with clindamycin, which has a boxed warning.

C. diff infection

All antibiotics have a risk for C diff. infection but the highest risk is with ____, which has a boxed warning.

clindamycin

Antimicrobial stewardship program interventions include.... (5)

1) Pharmacokinetic monitoring

2) Clinical decision support

3) Restricted use of select abx such as w/ prior auth

4) Prospective audit

5) Timely transitions from IV to PO

Name the hydrophilic abx (5)

1) Beta-lactams

2) Aminoglycosides

3) Vancomycin

4) Daptomycin

5) Polymyxins

Name the lipophilic abx (5)

1) Quinolones

2) Macrolides

3) Rifampin

4) Linezolid

5) Tetracyclines

Name 4 characteristics of hydrophilic abx:

1) ___ volume of distribution => ___ tissue penetration

2) Mostly ___ eliminated

3) ___ intracellular conc => not active against ___ pathogens

4) ___ bioavailability => IV:PO ratio is ___

1) Small volume of distribution => less tissue penetration

2) Mostly renally eliminated

3) Low intracellular conc => not active against atypical pathogens

4) Poor bioavailability => IV:PO ratio is NOT 1:1

Name 4 characteristics of lipophilic abx:

1) ___ volume of distribution => ___ tissue penetration

2) Mostly ___ metabolized

3) ___ intracellular conc => active against ___ pathogens

4) ___ bioavailability => IV:PO ratio is ___

1) Large volume of distribution => better tissue penetration

2) Mostly hepatically metabolized

3) High intracellular conc => active against atypical pathogens

4) Excellent bioavailability => IV:PO ratio is often 1:1

Drugs with ____ killing can be dosed less frequently and in higher doses.

Select all.

a) concentration-dependent

b) exposure-dependent

c) time-dependent

d) Cmax:MIC

e) AUC:MIC

f) Time > MIC

a) concentration-dependent

d) Cmax:MIC

Drugs with ____ killing can be dosed more frequently or each dose administered for a longer duration.

Select all.

a) concentration-dependent

b) exposure-dependent

c) time-dependent

d) Cmax:MIC

e) AUC:MIC

f) Time > MIC

c) time-dependent

f) Time > MIC

Cmax:MIC is aka

Concentration-dependent

AUC:MIC is aka

Exposure-dependent

Time > AUC is aka

Time-dependent

What abx exhibit concentration-dependent killing? (Cmax:MIC)

1) Aminoglycosides

2) Quinolones

3) Daptomycin

What abx exhibit exposure-dependent killing? (AUC:MIC)

1) Vancomycin

2) Macrolides

3) Tetracyclines

4) Polymyxins

What abx exhibit time-dependent killing? (time > MIC)

Beta-lactams (penicillins, cephalosporins, carbapenems)

Name the 3 drug classes under beta-lactams

1) Penicllins

2) Cephalosporins

3) Carbapenems

Draw a beta-lactam ring

What is the MOA of penicillins, cephalosporins and carbapenems?

Inhibit bacterial cell wall synthesis by binding to penicillin-binding proteins to prevent the final step of peptidoglycan synthesis

What microbes are beta-lactams not active against?

1) MRSA

2) Atypical organisms: Chlamydophila, Legionella, Mycoplasma

Natural penicillins are active against (3)

They are not active against (2)

Active:

1) Streptococci spp

2) Enterococci spp

3) Gram-positive anaerobes aka mouth flora

Not active against:

1) Staphylococci spp

2) Gram-negatives

Name the natural penicillins (3)

1) Penicillin V Potassium (Penicillin VK)

2) Penicillin G Aqueous

3) Penicillin G Benzathine (Bicillin L-A)

What are these drugs active against:

1) Penicillin V Potassium (Penicillin VK)

2) Penicillin G Aqueous

3) Penicillin G Benzathine (Bicillin L-A)

(3 gram pos)

1) Streptococci spp

2) Enterococci spp

3) Gram-positive anaerobes aka mouth flora

Antistaphylococcal penicillins are active against (2)

They are not active against (3)

Active:

1) MSSA

2) Streptococci spp

Not active against:

1) Enterococci spp

2) Gram-negatives

3) Anaerobes

What are these drugs active against:

1) Dicloxacillin

2) Nafcillin

3) Oxacillin

(2 gram pos)

Active:

1) MSSA

2) Streptococci spp

Name the 3 antistaphylococcal penicillins

1) Dicloxacillin

2) Nafcillin

3) Oxacillin

Name the 2 aminopenicillins

1) Amoxicillin

2) Ampicillin

What are these drugs active against:

1) Amoxicillin

2) Ampicillin

(3 gram pos and 4 gram neg)

1) Streptococci spp

2) Enterococci spp

3) Gram-pos anaerobes aka mouth flora

Gram-neg

4) Haemophilus

5) Neisseria

6) Proteus

7) E. coli

Ampicillin is also active against Listeria

Aminopenicillins are active against (7)

___ is also active against Listeria

(3 gram pos and 4 gram neg)

1) Streptococci spp

2) Enterococci spp

3) Gram-pos anaerobes aka mouth flora

Gram-neg

4) Haemophilus

5) Neisseria

6) Proteus

7) E. coli

Ampicillin is also active against Listeria

Name the two aminopenicillin/beta-lactamase drugs

Amoxicillin/clavulanate (Augmentin, Augmentin ES-600)

Ampicillin/sulbactam (Unasyn)

What are these drugs active against:

Amoxicillin/clavulanate (Augmentin, Augmentin ES-600)

Ampicillin/sulbactam (Unasyn)

(4 gram pos and 8 gram neg)

1) Streptococci spp

2) Enterococci spp

3) Gram-pos anaerobes aka mouth flora

4) MSSA

Gram-neg:

5) Haemophilus

6) Neisseria

7) Proteus

8) E. coli

9) Haemophilus

10) Neisseria

11) Klebsiella

12) Gram-neg anaerobes like B. fragilis

Ampicillin is also active against Listeria

Aminopenicillins/beta-lactamase drugs are active against (12)

___ is also active against Listeria

(4 gram pos and 8 gram neg)

1) Streptococci spp

2) Enterococci spp

3) Gram-pos anaerobes aka mouth flora

4) MSSA

Gram-neg:

5) Haemophilus

6) Neisseria

7) Proteus

8) E. coli

9) Haemophilus

10) Neisseria

11) Klebsiella

12) Gram-neg anaerobes like B. fragilis

Ampicillin is also active against Listeria

Name an extended-spectrum penicillin

Piperacillin/Tazobactam (Zosyn)

Piperacillin/Tazobactam (Zosyn) is active against (3 gram pos and 14 gram neg)

1) Streptococci spp

2) Enterococci spp

3) Gram-pos anaerobes aka mouth flora

4) MSSA

Gram-neg:

5) Haemophilus

6) Neisseria

7) Proteus

8) E. coli

9) Haemophilus

10) Neisseria

11) Klebsiella

12) Gram-neg anaerobes like B. fragilis

13) Citrobacter

14) Acinetobacter

15) Providencia

16) Enterobacter

17) Serratia

18) Pseudomonas !!!

Do any penicillins cover MRSA?

No

Drug formulation for Penicillin V Potassium

PO

Drug formulation for Penicillin G Aqueous

IV

Drug formulation for Penicillin G Benzathine (Bicillin-LA)

IM

Penicillin G Benzathine (Bicillin-LA)

Black box warning? (1)

1) Not for IV use

(only for IM)

What penicillins does not require renal dose adjustments?

antistaphylococcal penicillins:

Dicloxacillin, Nafcillin, Oxacillin

What cephalosporin does not require renal dose adjustment?

Ceftriaxone

Drug formulation for Nafcillin and Oxacillin

IV

Drug formulation for Dicloxacillin

PO

Drug formulation for Amoxicillin and Augmentin

PO

Drug formulation for Ampicillin and Ampicillin/sulbactam (Unasyn)?

They are preferably diluted in what?

IV

Diluted in NS (0.9%)

Drug formulation for Zosyn

IV

Special Augmentin dosing for CrCl < ____

CrCl < 30

Do not use the 875 mg strength or the extended-release

If improperly dosed and there is an accumulation of penicillins/cephalosporins/carbapenems in the body, what ADE are we worried for?

Seizures

ADE with properly dosed Penicillins and Cephalosporins (5)

1) GI upset

2) Diarrhea

3) Rash (including SJS/TEN)

4) Allergic rxns/anaphylaxis

5) Hemolytic anemia => w/ a pos Coombs test

What lab monitoring is done with IV penicillins, cephalosporins and carbapenems?

Renal fxn

What penicillins are preferred for MSSA tx?

Antistaphylococcal penicillins:

1) Dicloxacillin

2) Nafcillin

3) Oxacillin

The PO formulation of Ampicillin is rarely used due to ___

poor bioavailability

A pt is ready to go from IV ampicillin to PO. What drug do you choose and why?

Choose amoxicillin PO

Ampicillin PO has poor bioavailability

Augmentin ES-600 has a lower concentration of ___ causing a lower risk of ___

Clavulanate; diarrhea

What drug can increase the lvls of beta-lactams by interfering with renal excretion?

It's sometimes used intentionally in severe inf to increase beta-lactam lvls.

Probenecid

Penicillins and methotrexate

Penicillins can increase the lvl of methotrexate

Beta-lactams (except for ___ and ___ ) can enhance the anticoagulant effect of ____

Beta-lactams (except for nafcillin and dicloxacillin) can enhance the anticoagulant effect of warfarin

What 2 beta-lactams inhibits the anticoagulant effect of warfarin?

Nafcillin

Dicloxacillin

All penicillins should be avoided in patients with what allergy?

What are the two exceptions?

Beta-lactam allergy

1) Tx of syphilis in pregnancy

2) Pts w/ poor adherence/follow-up

=> desensitize and tx w/ penicillin G benzathine

Pts that have a beta-lactam allergy but still require tx with a pencillin, what is the DOC after pts are desensitized?

Penicillin G benzathine

What penicillin is a first-line tx for pharyngitis (strep throat)?

Penicillin V Potassium (Penicillin VK)

What penicillin is used in H. pylori regimens?

Amoxicillin

What is the first-line tx for acute otitis media (AOM)? (2)

What is the pediatric dose in mg/kg/day?

1) Amoxicillin 80-90 mg/kg/day

2) Augmentin 90 mg/kg/day

What penicillin can be used to tx bacterial sinusitis?

Augmentin

What is the DOC for infective endocarditis prophylaxis before dental procedures?

Amoxicillin

What is the only penicillin active against pseudomonas?

Zosyn

How can Zosyn dosing be optimized using time-dependent killling?

Extended infusions (4 hrs) can be used to maximize time > MIC

Cephalosporins are not active against what two bacterial groups?

1) Enterococcus spp

2) Atypical organisms

Name some 1st gen cephalosporins (2)

1) Cefazolin (Ancef)

2) Cephalexin (Keflex)

What are these drugs active against: (4 gram pos and 3 gram neg)

1) Cefazolin (Ancef)

2) Cephalexin (Keflex)

1) Streptococci spp

2) Staphylococci spp

3) MSSA

4) Gram-positive anaerobes aka mouth flora

5) Proteus

6) E. coli

7) Klebsiella

What bacteria do 1st gen cephalosporins cover? (4 gram pos and 3 gram neg)

1) Streptococci spp

2) Staphylococci spp

3) MSSA

4) Gram-positive anaerobes aka mouth flora

5) Proteus

6) E. coli

7) Klebsiella

Name some 2nd gen cephalosporins (3)

1) Cefuroxime

2) Cefotetan

3) Cefoxitin

What are these drugs active against: (2 gram pos and 5 gram neg)

1) Cefuroxime

2) Cefotetan

3) Cefoxitin

1) Staphylococci spp

2) Streptococcus pneumoniae

3) Haemophilus

4) Neisseria

5) Proteus

6) E. coli

7) Klebsiella

Cefotetan and cefoxitin have added activity against gram-neg anaerobes like Bacteroides fragilis, as well as gram-pos mouth flora

What bacteria do 2nd gen cephalosporins cover? (2 gram pos and 5 gram neg)

What do Cefotetan and cefoxitin have added activity against?

1) Staphylococci spp

2) Streptococcus pneumoniae

3) Haemophilus

4) Neisseria

5) Proteus

6) E. coli

7) Klebsiella

Cefotetan and cefoxitin have added activity against gram-neg anaerobes like Bacteroides fragilis, as well as gram-pos mouth flora

Name some 3rd gen group 1 cephalosporins (2)

1) Cefdinir

2) Ceftriaxone

What are these drugs active against: (5 gram-pos and 5 gram neg)

1) Cefdinir

2) Ceftriaxone

1) Streptococcus pneumoniae

2) viridans group streptococci

3) Staphylococci

4) MSSA

5) Gram-pos anaerobes (mouth flora)

1) Haemophilus

2) Neisseria

3) Proteus

4) E. coli

5) Klebsiella

What bacteria do 3rd gen group 1 cephalosporins? (5 gram-pos and 5 gram neg)

1) Streptococcus pneumoniae

2) viridans group streptococci

3) Staphylococci

4) MSSA

5) Gram-pos anaerobes (mouth flora)

1) Haemophilus

2) Neisseria

3) Proteus

4) E. coli

5) Klebsiella