Penicillin V and Penicillin G: Acid Stability and Side Effects
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Questions and Answers

Which of the following bacteria is cefuroxime NOT used to treat?

  • Streptococcus pneumoniae
  • Haemophilus influenzae
  • Klebsiella
  • P.aeruginosa (correct)

    • What is the primary indication for usage of cefoxitin?

  • Meningitis caused by gram-negative bacilli
  • Respiratory tract infections
  • Otitis and sinusitis
  • Abdominal and pelvic infections (correct)

    • Which of the following is NOT a characteristic of third-generation cephalosporins?

  • Highly active against gram-negative organisms
  • Effective against gram-positive organisms (correct)
  • Resistance to beta-lactamase
  • Penetrate to the CSF

    • Which of the following is a-drug of choice for meningitis caused by P.aeruginosa?

    <p>Ceftazidime</p> Signup and view all the answers

    What is the mechanism of action of glycopeptides such as vancomycin?

    <p>Disruption of cell wall biosynthesis</p> Signup and view all the answers

    Which of the following is a fifth-generation cephalosporin?

    <p>Ceftaroline</p> Signup and view all the answers

    What is the primary use case for cefepime?

    <p>Health care and hospital-associated pneumonias</p> Signup and view all the answers

    What is the mechanism of action of beta-lactams such as cephalosporins?

    <p>Disruption of cell wall biosynthesis</p> Signup and view all the answers

    What is the reason for the broadened spectrum of ampicillin and amoxicillin compared to penicillin G?

    <p>Increased ability to penetrate the gram negative cell envelope</p> Signup and view all the answers

    What is the primary difference between ampicillin and amoxicillin?

    <p>Acid stability</p> Signup and view all the answers

    Which of the following organisms is not susceptible to the antimicrobial spectrum of ampicillin?

    <p>Staphylococcus aureus</p> Signup and view all the answers

    Why is amoxicillin preferred over ampicillin for oral therapy?

    <p>Amoxicillin is more acid stable</p> Signup and view all the answers

    What is the primary use of piperacillin?

    <p>Infections caused by Pseudomonas aeruginosa</p> Signup and view all the answers

    What is the common side effect of ampicillin that occurs more frequently than with any other penicillin?

    <p>Diarrhea</p> Signup and view all the answers

    Why is dosage reduction necessary for patients with renal impairment taking ampicillin?

    <p>To avoid toxicity</p> Signup and view all the answers

    What is the name of the extended-spectrum penicillin that is susceptible to beta-lactamases?

    <p>Piperacillin</p> Signup and view all the answers

    What is the main difference between Penicillin V and Penicillin G?

    <p>Penicillin V is stable in stomach acid, whereas Penicillin G is not</p> Signup and view all the answers

    Which of the following side effects is specifically associated with methicillin?

    <p>Nephritis</p> Signup and view all the answers

    What is the main reason why β-lactamase resistant penicillins are not used against non-penicillinase-producing staphylococci?

    <p>They are less effective against these bacteria</p> Signup and view all the answers

    What is the mechanism of resistance of methicillin-resistant Staphylococcus aureus to penicillinase-resistant penicillins?

    <p>Production of PBPs to which the penicillinase-resistant penicillins cannot bind</p> Signup and view all the answers

    Why are oral formulations of Nafcillin no longer available?

    <p>Due to its erratic and incomplete absorption from the GI tract</p> Signup and view all the answers

    What is the main difference between Oxacillin and Dicloxacillin?

    <p>Oxacillin is only administered intravenously, while Dicloxacillin is formulated for oral dosing</p> Signup and view all the answers

    What is the treatment of choice for methicillin-resistant Staphylococcus aureus infections?

    <p>Vancomycin</p> Signup and view all the answers

    Which of the following is a characteristic of broad-spectrum penicillins?

    <p>Activity against a wide range of bacteria</p> Signup and view all the answers

    What is the primary reason for administering cilastatin with imipenem?

    <p>To inhibit the metabolism of imipenem and increase its urinary concentrations</p> Signup and view all the answers

    What is the primary mechanism of action of aztreonam?

    <p>Inhibition of bacterial cell wall synthesis</p> Signup and view all the answers

    Which of the following bacteria is NOT susceptible to aztreonam?

    <p>Staphylococcus aureus</p> Signup and view all the answers

    What is the incidence of cross-sensitivity with penicillins in patients allergic to imipenem?

    <p>About 1%</p> Signup and view all the answers

    What is the elimination half-life of imipenem?

    <p>About 1 hour</p> Signup and view all the answers

    What is the primary advantage of aztreonam over other beta-lactam antibiotics?

    <p>It is highly resistant to beta-lactamases</p> Signup and view all the answers

    What is the most common adverse effect of imipenem?

    <p>Gastrointestinal effects</p> Signup and view all the answers

    What is the percentage of imipenem that is excreted unchanged in the urine when administered with cilastatin?

    <p>About 70%</p> Signup and view all the answers

    What is the reason for the increased activity of second-generation cephalosporins against gram-negative bacteria?

    <p>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</p> Signup and view all the answers

    Against which type of bacteria do first-generation cephalosporins have only modest activity?

    <p>Gram-negative bacteria</p> Signup and view all the answers

    Which of the following statements about third-generation cephalosporins is true?

    <p>They are more active against gram-negative aerobes than first- and second-generation agents</p> Signup and view all the answers

    What distinguishes fourth-generation cephalosporins from other generations?

    <p>High resistance to beta-lactamases</p> Signup and view all the answers

    Which of the following cephalosporins reaches clinically effective concentrations in the CSF?

    <p>Third-generation cephalosporins</p> Signup and view all the answers

    What is the unique feature of cefepime among cephalosporins?

    <p>High resistance to beta-lactamases</p> Signup and view all the answers

    Which generation of cephalosporins is most active against staphylococci and nonenterococcal streptococci?

    <p>First-generation cephalosporins</p> Signup and view all the answers

    What is the limitation of second-generation cephalosporins?

    <p>Lack of activity against Pseudomonas aeruginosa</p> Signup and view all the answers

    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

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    Description

    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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