Antibacterials 6

Question 1

Describe Cotrimoxazole? MOA?

Answer 1

• Combination of trimethoprim & sulfamethoxazole
• Bactericidal

Mechanism of action:
• Synergistic: inhibition of sequential steps in
tetrahydrofolic acid synthesis

Question 2

Cotrimoxazole Clinical Applications?

Answer 2

• Uncomplicated UTI’s (drug of choice)
• Commonly used in treatment of opportunistic
infections (in immunocompromised)
• Upper respiratory, ear and sinus infections

Question 3

Cotrimoxazole PK?

Answer 3

• Oral admin. generally (can be given IV)

* Well distributed (including CSF)

Question 4

Cotrimoxazole AE?

Answer 4

• Dermatologic (common)
• GI
• Hematologic (hemolytic anemia)
• AIDS patients = higher incidence
• Contraindicated in pregnancy (esp. 1st trimester)

Question 5

Describe Metronidazole

Answer 5

• Antimicrobial, amebicide & antiprotozoal
• Activity against anaerobic bacteria
• Bactericidal

Question 6

Metronidazole MOA?

Answer 6

• Anaerobic conditions are vital for optimal activity
• Undergoes reductive bioactivation of its nitro group by
ferredoxin
• Forms cytotoxic products that interfere with nucleic acid
synthesis -> damage DNA

Question 7

Metronidazole Clinical Applications?

Answer 7

• Pseudomembranous colitis
• Anaerobic or mixed intra-abdominal infections
• Vaginitis
• Brain abscesses
• H.pylori eradication (in combination)

Question 8

Metronidazole PK?

Answer 8

• Oral, IV, rectal or topical
• Wide distribution (including CSF)
• Elimination = hepatic metabolism

Question 9

Metronidazole AE?

Answer 9

• Disulfiram-like effect (avoid alcohol)
• Headache, dark coloration of urine, metallic taste
• GI irritation, stomatitis, peripheral neuropathy (prolonged
use)
• Leukopenia, dizziness, ataxia (rarer)
• Opportunistic fungal infections
• Use generally not advised in 1st trimester

Question 10

Describe Polymyxin B?

Answer 10

• Basic peptides
• Activity against Gram-negative bacteria
• Gram-positive bacteria are resistant
• Bactericidal

Question 11

MOA of Polymyxin B?

Answer 11

• Act as cationic detergents
• Attach to and disrupt bacterial cell membranes
• Also, bind to and inactivate endotoxin

Question 12

Polymyxin B Clinical Applications?

Answer 12

• Mostly topical treatment for infected superficial skin
lesions
• Possible emerging role as parenteral agent for salvage
therapy of infections caused by resistant Acinetobacter
baumannii, P.aeruginosa and Enterobacteriaceae strains

Question 13

Polymyxin AE?

Answer 13

• Few when used topically

* Given systemically = extremely nephrotoxic

Question 14

Describe Urinary antiseptics and use?

Answer 14

• Oral agents with antibacterial activity in urine but little or no systemic effect
• Use is limited to prophylaxis and treatment of lower UTI’s

Question 15

Describe Nitrofurantoin?

Answer 15

• Bacteriostatic & bactericidal
• Active against many Gram-positive and Gram-negative
bacteria

Question 16

Nitrofurantoin MOA?

Answer 16

• Reduction of nitrofurantoin by bacteria in the urine leads
to formation of reactive intermediates that subsequently
damage bacterial DNA
• Slow emergence of resistance and no cross-resistance

Question 17

Nitrofurantoin PK and AE?

Answer 17

Pharmacokinetics
• Rapid elimination (only achieves adequate concentrations
in urine)

Adverse Effects
• Anorexia, nausea & vomiting.
•Neuropathies, hemolytic anemia (G6PD deficient patients)
•Pulmonary injury (rare)

Question 18

Nitrofurantoin Contraindications?

Answer 18

• Significant renal insufficiency
• Pregnancy at term (38-42 weeks)
• Infants <1 month (risk of hemolytic anemia)

Question 19

Antimicrobial effect on fetus and neonate? Aminoglycoside? Tetracycline,Glycilines? Sulfonamides? Choramphenicol? Fluoroquinolones? Nitrofurantion? Trimethoprim? Metronidazole?

Answer 19

Aminoglycosides -Possible damage to the eighth
cranial nerve of the fetus

Tetracyclines, Glycylcyclines -Tooth enamel dysplasia, inhibition
of bone growth

Sulfonamides Kernicterus (displacement of
bilirubin from serum albumin)

Chloramphenicol Gray baby syndrome

Fluoroquinolones Tendon rupture/damage

Nitrofurantion Hemolytic Anemia

Trimethoprim Folate deficiency

Metronidazole Unknown safety

Question 20

Surgical Antimicrobial Prophylaxis Cardiothoracic?

Answer 20

Antimicrobials:
Routine: Cefazolin
MRSA: Cefazolin +
vancomycin

Penicillin-allergic patient:
Vancomycin + aztreonam (routine & MRSA)

Question 21

Surgical Antimicrobial Prophylaxis Colorectal?

Answer 21

Antimicrobials:
Ampicillin/sulbactam

Penicillin-allergic patient:
Ciprofloxacin +
metronidazole or
ciprofloxacin +
clindamycin

Question 22

Surgical Antimicrobial Prophylaxis General Surgery?

Answer 22

Antimicrobials: Cefazolin

Penicillin-allergic patient:
Vancomycin or
clindamycin

Question 23

Surgical Antimicrobial Prophylaxis Neurosurgical?

Answer 23

Antimicrobials: Cefazolin

Penicillin-allergic patient: Vancomycin

Question 24

Surgical Antimicrobial Prophylaxis Orthopedics?

Answer 24

Antimicrobials: Cefazolin

Penicillin-allergic patient:
Vancomycin or
clindamycin

Question 25

Surgical Antimicrobial Prophylaxis Vascular Surgery?

Answer 25

Antimicrobials: Cefazolin or cefuroxime Penicillin-allergic patient: Vancomycin or clindamycin

Question 26

Anti-staphylococcal penicillins used against which bacteria?

Answer 26

beta-lactamase producing bacteria | Gram +ve

Question 27

Carbapenems used against which bacteria?

Answer 27

beta-lactamase producing bacteria | Gram +ve and –ve

Question 28

Aztreonam used against which bacteria?

Answer 28

beta-lactamase producing bacteria | Gram –ve

Question 29

Vancomycin used against which bacteria?

Answer 29

MRSA, enterococci

Question 30

Daptomycin used against which bacteria?

Answer 30

MRSA, enterococci, VRE

Question 31

Tigecycline used against which bacteria?

Answer 31

MDR Gram +ve and some Gram –ve bacteria

Question 32

Streptogramins used against which bacteria?

Answer 32

MRSA, VRE

Question 33

Linezolid used against which bacteria?

Answer 33

MRSA, VRE

Question 34

Rifampin used against which bacteria?

Answer 34

MRSA