Antibiotics Flashcards
What is the most common mechanism of antibiotic resistance in penicillin?
Beta-lactamases produced by bacteria, such as Staphylococcus aureus. These enzymes degrade the beta-lactam ring of penicillin, rendering them ineffective.
Which antibiotic is the standard therapy for primary, secondary, or early latent syphilis?
A single dose of benzathine penicillin G
Which form of penicillin is orally administered and more stable in acidic conditions?
Penicillin V. It is typically used for minor infections due to its poor bioavailability, narrow spectrum, and requirement of multiple daily dosing.
What is the degree of cross-reactivity between penicillin and cephalosporins in patients with a penicillin allergy?
10%
Which test is positive when autoimmune hemolytic anemia occurs as an adverse effect of penicillin administration?
Direct Coombs Test. When autoimmune hemolytic anemia occurs due to antibodies binding to the surface of red blood cells as an adverse effect of penicillin administration, the direct Coombs test would be positive.
What best describes the mechanism of bacterial resistance against penicillinase-resistant penicillins acquired by methicillin-resistant Staphylococcus aureus (MRSA)?
MRSA contains altered penicillin binding proteins, which prevents drug binding and renders these drugs ineffective.
What feature is taken by anti-staphylococcal penicillins (i.e. nefcillin) to evade beta-lactamase?
Bulky R-groups that prevent beta-lactamase from binding to their molecule, thus allowing them to evade the antibiotic-degrading actions of beta-lactamase.
For which of the following bacterial infections is empiric treatment with nafcillin, oxacillin, or dicloxacillin most appropriate?
Mild to moderate localized staph skin and soft tissue infections.
When compared to other penicillins, piperacillin and ticarcillin have important additional indications due to activity against which of the following bacteria?
Pseudomonas is a gram-negative aerobic bacteria that can cause a wide variety of serious infections, including pneumonia, urinary tract infection, and otitis externa. Piperacillin and ticarcillin are extended-spectrum penicillins, which unlike other penicillins, can be used to treat Pseudomonas infections.
What is the mechanism by which Enterococcus may become resistant to ampicillin?
B-lactamase. Ampicillin-resistant strains of Enterococcus produce β-lactamase, which cleaves the β-lactam ring and prevents β-lactam antibiotics from blocking bacterial transpeptidase peptidoglycan cross-linking. Resistant Enterococcus infections may be treated with ampicillin plus sulbactam or with vancomycin.
What is the difference in oral bioavailability of amoxicillin and ampicillin?
Amoxicillin has better oral bioavailability. Ampicillin is IV.
What are the 4 most common adverse events for ampicillin and amoxicillin?
Steven Johnson syndrome, toxic epidermal necrolysis, skin rash with viral illness, and drug-induced liver injury.
What is the benefit of pairing aminopenicillins with tazobactam or sulbactam?
Tazobactam and sulbactam inhibit bacterial β-lactamases. These drugs protect penicillin antibiotics from destruction by β-lactamases, enabling penicillin-based therapy for bacteria such as methicillin-sensitive Staph aureus.
Aztreonam is most effective in treating infections caused by which pathogens?
Aerobic gram-negative rods
List the top 3 side effects of imipenem
- skin rash
- GI - N,V,D
- Lowers seizure threshold
Does Vancomycin treat gram-neg or gram-pos bacteria?
Gram-positive
Which Abx should be paired with Vancomycin to treat bacterial meningitis (in otherwise healthy adult)?
Ceftriaxone. Streptococcus pneumoniae is the most common cause of bacterial meningitis in healthy adults aged 6-60 years old. Because of the increasing prevalence of penicillin resistant Streptococcus pneumoniae, vancomycin is used while awaiting culture and sensitivity testing. Vancomycin should be paired with a third generation cephalosporin such as ceftriaxone, cefotaxime, or ceftazidime to cover common gram negative causes of bacterial meningitis.
Which pathogen would vancomycin NOT be effect against?
1. Enterococcus faecalis
2. MRSA
3. MSSA
4. Pseudomonas aeruginosa
- Pseudomonas because it is a gram-neg bacteria.
What is the mechanism of action of vancomycin?
Vancomycin is a glycopeptide antibiotic which obstruct the synthesis of bacterial cell walls. Vancomycin binds to the cell wall precursors D-alanine-D-alanine. By binding to these oligopeptides, vancomycin inhibits the synthesis of peptidoglycan necessary to make up the cell wall.
Which medication is specifically used for uncomplicated UTIs in women?
Fosfomycin
A patient is referred for one of the following complaints, leading you to suspect recent fluoroquinolone usage. What is the referral for?
A. Hearing loss
B. Tendon rupture
C. Osteonecrosis
D. Oliguria
B. Tendon Rupture. One of the most significant potential adverse effects of fluoroquinolones is tendon rupture, particularly in elderly patients and those on glucocorticoids.
Which of the following best describes the mechanism of action of fluoroquinolones?
A. They inhibit bacterial cell wall synthesis.
B. They disrupt bacterial protein synthesis.
C. They inhibit bacterial topoisomerases (DNA replication).
D. They inhibit bacterial folic acid synthesis.
C. Inhibit topoisomerases. Fluoroquinolones inhibit bacterial topoisomerases, such as DNA gyrase. This disrupts DNA replication and transcription and leads to the death of the bacteria. They do not affect protein or cell wall synthesis or folic acid metabolism.
In which of the following conditions are fluoroquinolones contraindicated?
A. Pregnancy
B. Diabetes
C. Hypertension
D. Asthma
A. Pregnancy. Fluoroquinolones are contraindicated in pregnancy because they can potentially cause harm to the fetus. They are also not usually recommended for use in children under the age of 10 due to the risk of damage to growing cartilage.
A patient being treated with fluoroquinolones for pneumonia is found to have an abnormal EKG. What is the most likely abnormality?
A. ST-segment elevation
B. Pathologic Q waves
C. Prolonged QT interval
D. Peaked T waves
C. Prolonged QT interval. Quinolones can prolong the QT interval by blocking certain cardiac potassium channels. It is especially important to consider this risk in patients who are taking other QT-prolonging medications.
