Beta-Lactam Antibiotics: Penicillins and Mechanism of Action
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Questions and Answers

What is the mechanism of action of beta-lactam antibiotics?

  • Inhibition of protein synthesis
  • Inhibition of cell wall synthesis by binding to specific receptors (PBPs) and inhibiting transpeptidase enzymes (correct)
  • Disruption of cell membrane function
  • Inhibition of DNA replication

    • What is the effect of beta-lactamase on the activity of beta-lactam antibiotics?

  • Increases antibacterial activity
  • Has no effect on antibacterial activity
  • Converts beta-lactam antibiotics to a more active form
  • Decreases antibacterial activity (correct)

    • Which of the following is a characteristic of penicillin G?

  • It is resistant to gastric acid (correct)
  • It is resistant to beta-lactamase
  • It is primarily excreted in the bile
  • It is a broad-spectrum antibiotic

    • What is the purpose of combining beta-lactam antibiotics with beta-lactamase inhibitors?

    <p>To prevent the degradation of the antibiotic by beta-lactamase</p> Signup and view all the answers

    Which of the following is a use of procaine and benzathine penicillin G?

    <p>Treatment of syphilis</p> Signup and view all the answers

    What is the half-life of penicillin G?

    <p>30 minutes to 1 hour</p> Signup and view all the answers

    What is the main difference between penicillin and cephalosporins?

    <p>Penicillin has a beta-lactam ring, while cephalosporins have a dihydrothiazine ring.</p> Signup and view all the answers

    What is the main mechanism of resistance to penicillin?

    <p>Hydrolysis by beta-lactamase.</p> Signup and view all the answers

    Which of the following antibiotics is used to treat Staphylococcal infections?

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

    What is the main advantage of using Piperacillin and Ticarcillin over Ampicillin and Amoxicillin?

    <p>They are more effective against Gram-negative organisms.</p> Signup and view all the answers

    What is the main characteristic of 3rd generation cephalosporins?

    <p>They are more effective against Gram-negative organisms.</p> Signup and view all the answers

    What is the main route of elimination for most cephalosporins?

    <p>Renal tubular excretion.</p> Signup and view all the answers

    What is the mechanism of action of Clindamycin?

    <p>Binding to the 50S ribosomal subunit</p> Signup and view all the answers

    What is the primary route of elimination of Clindamycin?

    <p>Hepatic metabolism and renal excretion</p> Signup and view all the answers

    Which of the following is a common mechanism of resistance to Clindamycin?

    <p>All of the above</p> Signup and view all the answers

    What is a common side effect of Clindamycin?

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

    What is a common indication for Clindamycin?

    <p>Skin and soft tissue infections</p> Signup and view all the answers

    What is the mechanism of action of quinupristin-dalfopristin against gram-positive cocci?

    <p>Inhibition of protein synthesis</p> Signup and view all the answers

    What is the primary route of excretion for quinupristin-dalfopristin?

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

    What is the Primary indication for the use of quinupristin-dalfopristin?

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

    What is the half-life of quinupristin?

    <p>0.85 hours</p> Signup and view all the answers

    What is the mechanism of resistance to quinupristin-dalfopristin?

    <p>All of the above</p> Signup and view all the answers

    What is the primary limitation of using linezolid?

    <p>Risk of thrombocytopenia</p> Signup and view all the answers

    What is the mechanism of action of sulfonamides?

    <p>Inhibitors of folic acid synthesis</p> Signup and view all the answers

    What is the consequence of displacing bilirubin from plasma protein binding?

    <p>Kernicterus in neonates</p> Signup and view all the answers

    What is the primary route of excretion for sulfonamides?

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

    What is the indication for Sulfasalazine?

    <p>Inflammatory bowel diseases</p> Signup and view all the answers

    What is the consequence of crystalluria in sulfonamide therapy?

    <p>Crystalluria and increased susceptibility to Gram-positive and Gram-negative infections</p> Signup and view all the answers

    What is the mechanism of action of Trimethoprim?

    <p>Inhibitor of dihydrofolate reductase</p> Signup and view all the answers

    What is the consequence of sulfonamide toxicity on the hematological system?

    <p>All of the above</p> Signup and view all the answers

    What is the indication for Cotrimoxazole?

    <p>All of the above</p> Signup and view all the answers

    What is the effect of sulfonamides on mammalian cells?

    <p>Cause inability to synthesize folic acid</p> Signup and view all the answers

    What is the half-life of Sulfamethoxazole?

    <p>10-12 hours</p> Signup and view all the answers

    Study Notes

    Penicillin and its Derivatives

    • Penicillin V: Effective for oropharyngeal infections following dental extraction.
    • Very-Narrow-Spectrum Penicillinase-Resistant Agents: Includes Methicillin, Nafcillin, and Oxacillin; resistant to penicillinase.
    • Methicillin: Prototype agent for treating staphylococcal infections; known to cause nephritis.
    • Resistance: MRSA (methicillin-resistant Staphylococcus aureus) and MRSE (methicillin-resistant Staphylococcus epidermis) are resistant to methicillin.
    • Ampicillin and Amoxicillin: Broader spectrum; effective against Enterococci, E. coli, H. influenzae, L. monocytogenes (dangerous for pregnant women), P. mirabilis, and M. catarrhalis. Synergistic effect with aminoglycosides.
    • Piperacillin and Ticarcillin: Target gram-negative bacteria, including Pseudomonas, Enterobacter, and Klebsiella species; also show synergy with aminoglycosides.

    Cephalosporins

    • Structural Characteristics: Cephalosporins differ from penicillins with a dihydrothiazine ring and acyl side chains (R1 and R2).
    • Generations: Classified based on their development; 1st Generation (Cephalexin, Cefazolin) generally targets Gram-positive bacteria.
    • Pharmacokinetics: Metabolized in the liver, mainly excreted via renal tubular excretion, except Ceftriaxone and Cefoperazone (excreted in bile).
    • Resistance: Cephalosporins exhibit varying resistance profiles from 1st to 3rd Generation, increasing coverage against Gram-negative organisms.

    Clindamycin and Lincosamides

    • Clindamycin: Binds to the 50S ribosomal subunit, exhibiting bacteriostatic activity; effective against Gram-positive cocci and anaerobic bacteria.
    • Toxicities: Can lead to severe anaerobic infections, skin rashes, toxic shock syndrome, and superinfections.
    • Combination Therapy: Often paired with aminoglycosides for serious infections such as necrotizing fasciitis.

    Streptogramins

    • Quinupristin/Dalfopristin: Bactericidal against most Gram-positive cocci; effective against MRSA and vancomycin-resistant E. faecium.
    • Mechanism: Binds to the 50S ribosomal subunit, causing protein synthesis disruption.
    • Toxicities and Drug Interactions: May cause arthralgia-myalgia syndrome; interacts with drugs metabolized by CYP3A4.

    Oxazolidinones

    • Linezolid and Tidezolid: Bind to the 23S rRNA of the 50S ribosomal subunit; prevent ribosome formation and exhibit bacteriostatic activity against streptococci.

    Sulfonamides and Trimethoprim

    • Sulfonamides: Bacteriostatic agents that inhibit folic acid synthesis by competing with PABA; used for uncomplicated UTIs and ocular infections.
    • Trimethoprim: Inhibits dihydrofolate reductase, blocking the formation of active tetrahydrofolate.
    • Cotrimoxazole: Combination of trimethoprim and sulfamethoxazole; provides synergistic inhibition of folate synthesis and expanded activity against various infections.
    • Toxicities: Potential for hypersensitivity reactions, gastrointestinal disturbances, and hematologic toxicity.

    General Pharmacokinetics and Resistance

    • Basic Mechanism of Action (MOA): Beta-lactam antibiotics disrupt cell wall synthesis by inhibiting transpeptidase enzymes, leading to bacterial cell lysis.
    • Resistance: Common mechanisms include enzymatic hydrolysis by beta-lactamases and modifications in target sites.

    Important Considerations

    • Drug Interactions: Some antibiotics displace other drugs from plasma proteins, potentially increasing their free concentrations and toxicity.
    • Adverse Effects: Includes skin toxicity, gastrointestinal upsets, and possible renal implications, necessitating cautious use in specific populations, such as the elderly or with pre-existing conditions.

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    Description

    This quiz covers the characteristics and mechanism of action of beta-lactam antibiotics, specifically penicillins, including their MOA, pharmacokinetics, resistance, and drug interactions.

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