40 Questions
Which of the following bacteria is cefuroxime NOT used to treat?
P.aeruginosa
What is the primary indication for usage of cefoxitin?
Abdominal and pelvic infections
Which of the following is NOT a characteristic of third-generation cephalosporins?
Effective against gram-positive organisms
Which of the following is a-drug of choice for meningitis caused by P.aeruginosa?
Ceftazidime
What is the mechanism of action of glycopeptides such as vancomycin?
Disruption of cell wall biosynthesis
Which of the following is a fifth-generation cephalosporin?
Ceftaroline
What is the primary use case for cefepime?
Health care and hospital-associated pneumonias
What is the mechanism of action of beta-lactams such as cephalosporins?
Disruption of cell wall biosynthesis
What is the reason for the broadened spectrum of ampicillin and amoxicillin compared to penicillin G?
Increased ability to penetrate the gram negative cell envelope
What is the primary difference between ampicillin and amoxicillin?
Acid stability
Which of the following organisms is not susceptible to the antimicrobial spectrum of ampicillin?
Staphylococcus aureus
Why is amoxicillin preferred over ampicillin for oral therapy?
Amoxicillin is more acid stable
What is the primary use of piperacillin?
Infections caused by Pseudomonas aeruginosa
What is the common side effect of ampicillin that occurs more frequently than with any other penicillin?
Diarrhea
Why is dosage reduction necessary for patients with renal impairment taking ampicillin?
To avoid toxicity
What is the name of the extended-spectrum penicillin that is susceptible to beta-lactamases?
Piperacillin
What is the main difference between Penicillin V and Penicillin G?
Penicillin V is stable in stomach acid, whereas Penicillin G is not
Which of the following side effects is specifically associated with methicillin?
Nephritis
What is the main reason why β-lactamase resistant penicillins are not used against non-penicillinase-producing staphylococci?
They are less effective against these bacteria
What is the mechanism of resistance of methicillin-resistant Staphylococcus aureus to penicillinase-resistant penicillins?
Production of PBPs to which the penicillinase-resistant penicillins cannot bind
Why are oral formulations of Nafcillin no longer available?
Due to its erratic and incomplete absorption from the GI tract
What is the main difference between Oxacillin and Dicloxacillin?
Oxacillin is only administered intravenously, while Dicloxacillin is formulated for oral dosing
What is the treatment of choice for methicillin-resistant Staphylococcus aureus infections?
Vancomycin
Which of the following is a characteristic of broad-spectrum penicillins?
Activity against a wide range of bacteria
What is the primary reason for administering cilastatin with imipenem?
To inhibit the metabolism of imipenem and increase its urinary concentrations
What is the primary mechanism of action of aztreonam?
Inhibition of bacterial cell wall synthesis
Which of the following bacteria is NOT susceptible to aztreonam?
Staphylococcus aureus
What is the incidence of cross-sensitivity with penicillins in patients allergic to imipenem?
About 1%
What is the elimination half-life of imipenem?
About 1 hour
What is the primary advantage of aztreonam over other beta-lactam antibiotics?
It is highly resistant to beta-lactamases
What is the most common adverse effect of imipenem?
Gastrointestinal effects
What is the percentage of imipenem that is excreted unchanged in the urine when administered with cilastatin?
About 70%
What is the reason for the increased activity of second-generation cephalosporins against gram-negative bacteria?
Combination of increased affinity for PBPs of gram-negative bacteria, increased ability to penetrate the gram-negative cell envelope, and increased resistance to beta-lactamases
Against which type of bacteria do first-generation cephalosporins have only modest activity?
Gram-negative bacteria
Which of the following statements about third-generation cephalosporins is true?
They are more active against gram-negative aerobes than first- and second-generation agents
What distinguishes fourth-generation cephalosporins from other generations?
High resistance to beta-lactamases
Which of the following cephalosporins reaches clinically effective concentrations in the CSF?
Third-generation cephalosporins
What is the unique feature of cefepime among cephalosporins?
High resistance to beta-lactamases
Which generation of cephalosporins is most active against staphylococci and nonenterococcal streptococci?
First-generation cephalosporins
What is the limitation of second-generation cephalosporins?
Lack of activity against Pseudomonas aeruginosa
Study Notes
Penicillin Stability
- Penicillin V is stable in stomach acid, whereas penicillin G is not.
- Penicillin V has replaced penicillin G for oral therapy due to its acid stability.
Side Effects of Penicillins
- Hypersensitivity
- Diarrhea
- Nephritis (especially with methicillin)
- Neurotoxicity if given intrathecally
- Platelet dysfunction (carbenicillin and ticarcillin)
- Cationic toxicity
β-Lactamase Resistant Penicillins
- Examples: Flucloxacillin, methicillin, nafcillin, oxacillin, and dicloxacillin
- These agents have a very narrow antimicrobial spectrum and are used only against penicillinase-producing strains of staphylococci (Staph. aureus and Staph. epidermidis)
Methicillin-Resistant Staphylococcus aureus (MRSA)
- Resistance appears to result from the production of PBPs to which the penicillinase-resistant penicillins cannot bind.
- Vancomycin is the treatment of choice for MRSA.
Nafcillin, Oxacillin, and Dicloxacillin
- Nafcillin: usually administered IV, absorption from the GI tract is erratic and incomplete
- Oxacillin and dicloxacillin: similar in structure and pharmacokinetic properties, both are acid-stable, but only dicloxacillin is formulated for oral dosing
Broad-Spectrum Penicillins (Aminopenicillins)
- Examples: ampicillin and amoxicillin
- Have the same antimicrobial spectrum as penicillin G, plus increased activity against certain gram-negative bacilli
- Both are readily inactivated by beta-lactamases and hence are ineffective against most infections caused by Staph. aureus
Ampicillin
- Was the first broad-spectrum penicillin in clinical use
- Useful against infections caused by Enterococcus faecalis, Proteus mirabilis, E. coli, Salmonella, Shigella, and H. influenzae
- Common side effects: rash and diarrhea, both of which occur more frequently with ampicillin than with any other penicillin
Amoxicillin
- Similar to ampicillin in structure and actions
- More acid-stable than ampicillin, hence, when orally administered in equivalent doses, blood levels of amoxicillin are greater
- Produces less diarrhea than ampicillin, perhaps because less amoxicillin remains unabsorbed in the intestine
Extended-Spectrum Penicillin (Antipseudomonal Penicillin)
- Example: piperacillin
- Antimicrobial spectrum includes organisms that are susceptible to aminopenicillins plus Pseudomonas aeruginosa, Enterobacter species, Proteus (indole positive), Bacteroides fragilis, and many Klebsiella
- Piperacillin is susceptible to beta-lactamases and hence is ineffective against most strains of Staph. aureus
Cephalosporins
- First-generation cephalosporins: used primarily for infections with staphylococci and nonenterococcal streptococci
- Second-generation cephalosporins: have enhanced activity against gram-negative bacteria
- Third-generation cephalosporins: have a broad spectrum of antimicrobial activity, are considerably more active against gram-negative aerobes, and reach clinically effective concentrations in the CSF
- Fourth-generation cephalosporin: cefepime, highly resistant to beta-lactamases and has a very broad antibacterial spectrum
- Fifth-generation cephalosporin: ceftaroline, used to treat MRSA-associated infections
Polypeptide and Glycopeptide Antibacterial Agents
- Mechanism of action: inhibit the synthesis of cell walls and thereby promote bacterial lysis and death
- Examples: vancomycin, teicoplanin, and bacitracin
Imipenem
- Adverse effects: gastrointestinal effects (nausea, vomiting, diarrhea), superinfections with bacteria or fungi, and seizures
- Elimination half-life: about 1 hour
- Used to treat a wide range of infections, including those caused by gram-negative bacteria, gram-positive bacteria, and fungi
Monobactam
- Aztreonam: belongs to a class of beta-lactam antibiotics known as monobactams
- Mechanism of action: binds to PBP3, inhibiting bacterial cell wall synthesis and promoting cell lysis and death
- Antimicrobial spectrum: active only against gram-negative aerobic bacteria, including Neisseria species, H. influenzae, P. aeruginosa, and Enterobacteriaceae
- Not active against gram-positive bacteria and anaerobes
This quiz covers the difference between penicillin V and penicillin G, including their acid stability and side effects. It also touches on the different types of penicillins and their effects on the body.
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