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Questions and Answers
Which factor contributes to the instability of the β-lactam ring in penicillins?
Which factor contributes to the instability of the β-lactam ring in penicillins?
- Ionization of the carboxylic acid group
- Lack of structural variations in the acylamino side chain
- Presence of sulphur in the structure
- Increased strain on the β-lactam ring (correct)
What role does the carboxylate ion play in the action of penicillins?
What role does the carboxylate ion play in the action of penicillins?
- It stabilizes the β-lactam ring.
- It provides a physical barrier for the antibiotic.
- It increases the transport efficiency across bacterial membranes.
- It binds to the charged nitrogen of a lysine residue in the binding site. (correct)
What is a primary reason for the varied susceptibility of bacterial strains to penicillin?
What is a primary reason for the varied susceptibility of bacterial strains to penicillin?
- Presence of β-lactamase enzymes (correct)
- High levels of sulphur in bacterial cells
- Absence of acylamino side chains
- Universal access to the cell membrane
Why does penicillin have good activity against Gram-positive bacteria?
Why does penicillin have good activity against Gram-positive bacteria?
How does the structure of the acylamino side chain impact penicillin's effectiveness?
How does the structure of the acylamino side chain impact penicillin's effectiveness?
Which mechanism serves as a physical barrier that penicillin must overcome in Gram-negative bacteria?
Which mechanism serves as a physical barrier that penicillin must overcome in Gram-negative bacteria?
What effect does the presence of efflux pumps in Gram-negative bacteria have on penicillin?
What effect does the presence of efflux pumps in Gram-negative bacteria have on penicillin?
What is the significance of PBP mutations in bacterial resistance to penicillin?
What is the significance of PBP mutations in bacterial resistance to penicillin?
Which component is NOT part of the penicillin structure?
Which component is NOT part of the penicillin structure?
What type of amino acids are predominantly found in human biochemistry?
What type of amino acids are predominantly found in human biochemistry?
Which sugars form the backbone of the bacterial cell wall?
Which sugars form the backbone of the bacterial cell wall?
What is the role of transpeptidase enzymes in bacterial cell walls?
What is the role of transpeptidase enzymes in bacterial cell walls?
What distinguishes the penam derivatives in terms of structure?
What distinguishes the penam derivatives in terms of structure?
Which of the following best describes the peptide chains in bacterial cell walls?
Which of the following best describes the peptide chains in bacterial cell walls?
What is the significance of the D-alanine displacement during peptide chain linking?
What is the significance of the D-alanine displacement during peptide chain linking?
How do bacteria utilize racemase enzymes regarding amino acids?
How do bacteria utilize racemase enzymes regarding amino acids?
What is the primary reason penicillin G is not effective when taken orally?
What is the primary reason penicillin G is not effective when taken orally?
What effect can high doses of procaine penicillin have?
What effect can high doses of procaine penicillin have?
Which of the following statements about penicillin G procaine is true?
Which of the following statements about penicillin G procaine is true?
What is a consequence of the ring strain in penicillin G?
What is a consequence of the ring strain in penicillin G?
What is the main action of benzathine in penicillin G benzathine?
What is the main action of benzathine in penicillin G benzathine?
What factor enhances the passage of certain penicillins through the Gram-negative bacterial outer membrane?
What factor enhances the passage of certain penicillins through the Gram-negative bacterial outer membrane?
Which type of allergic reaction can penicillins cause?
Which type of allergic reaction can penicillins cause?
What role does procaine play in procaine penicillin?
What role does procaine play in procaine penicillin?
Which of the following is classified as a broad-spectrum antibiotic?
Which of the following is classified as a broad-spectrum antibiotic?
How does the introduction of an ionized or polar group into the α-position of penicillin G's side chain affect its activity?
How does the introduction of an ionized or polar group into the α-position of penicillin G's side chain affect its activity?
What limitation does penicillin exhibit due to β-lactamase sensitivity?
What limitation does penicillin exhibit due to β-lactamase sensitivity?
What is a common challenge associated with the oral absorption of Ampicillin?
What is a common challenge associated with the oral absorption of Ampicillin?
Amoxicillin is said to have better oral absorption than Ampicillin primarily because:
Amoxicillin is said to have better oral absorption than Ampicillin primarily because:
What is the primary reason simple methyl esters are not used as prodrugs for penicillins?
What is the primary reason simple methyl esters are not used as prodrugs for penicillins?
Which of the following statements is true regarding ticarcillin?
Which of the following statements is true regarding ticarcillin?
Which of the following modifications improves the oral activity of Ampicillin?
Which of the following modifications improves the oral activity of Ampicillin?
What is a key characteristic that distinguishes ureidopenicillins from carboxypenicillins?
What is a key characteristic that distinguishes ureidopenicillins from carboxypenicillins?
What type of antibiotic class do Amoxicillin, Carboxypenicillins, and Ureidopenicillins represent?
What type of antibiotic class do Amoxicillin, Carboxypenicillins, and Ureidopenicillins represent?
Why must ticarcillin be administered parenterally?
Why must ticarcillin be administered parenterally?
What advantage do ureidopenicillins have over carboxypenicillins?
What advantage do ureidopenicillins have over carboxypenicillins?
What is the effect of administering tazobactam with piperacillin?
What is the effect of administering tazobactam with piperacillin?
What is the relationship between aryl esters and β-lactam rings in the context of extended esters?
What is the relationship between aryl esters and β-lactam rings in the context of extended esters?
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Study Notes
Non-classical β-Lactams and Penicillins
- Penicillin possesses an unstable bicyclic ring composed of a 4-membered β-lactam ring fused with a 5-membered thiazolidine ring.
- Derived from amino acids cysteine and valine, the penicillin structure resembles a half-open book.
- Unsubstituted bicyclic lactams are classified as penam derivatives, while penicillin derivatives are known as penicillanic acid derivatives.
Mechanism of Action
- Penicillin targets bacterial cell walls, which are peptidoglycan structures made of N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG).
- Transpeptidase enzymes (penicillin-binding proteins—PBPs) facilitate cross-linking of peptide chains bound to NAM sugars, creating bacterial cell wall integrity.
- Bacteria contain racemase enzymes that convert L-amino acids (human biochemistry) to D-amino acids, influencing antibiotic activity.
Resistance to Penicillin
- Bacterial susceptibility to penicillin varies due to multiple factors:
- Physical barriers: Gram-positive bacteria allow easier penicillin access, while Gram-negative bacteria have an outer membrane that restricts it.
- β-lactamase enzymes: These enzymes can inactivate penicillin.
- PBPs: High levels of transpeptidase enzymes may outcompete penicillin.
- Affinity: Variations in transpeptidase affinity for penicillin impact efficacy.
- Efflux pumps: Allow Gram-negative bacteria to expel penicillin.
Challenges in Penicillin Efficacy
- Acid sensitivity restricts oral bioavailability, as penicillin G is broken down by stomach acids.
- Allergic reactions may occur due to covalent binding between penicillin and proteins after β-lactam ring opening.
Extended Penicillin Forms
- Short duration of action is an issue; solutions involve combining penicillin G with high-molecular weight amines like procaine or benzathine.
- Procaine Penicillin: Slow absorption after intramuscular (IM) injection, can cause CNS side effects at high doses.
- Benzathine Penicillin: Long-acting formulation, effective in preventing rheumatic fever.
Broad-Spectrum Antibiotics
- Broad-spectrum activity includes aminopenicillins, carboxypenicillins, and ureidopenicillins, characterized by an α-hydrophilic group for Gram-negative efficacy.
- Aminopenicillins (e.g., Ampicillin): Acid-stable, sensitive to β-lactamase, absorbed less effectively due to amphoteric characteristics.
- Amoxicillin: Improved absorption (80%), less disruption to gut flora.
Ticarcillin and Ureidopenicillins
- Ticarcillin: Sulfur-based analogue of carbenicillin, effective against Gram-negative infections, unstable in acid, administered parenterally.
- Ureidopenicillins: Better attributes than carboxypenicillins; generally more active against Gram-negative bacteria, also sensitive to β-lactamases, require injection.
- Tazobactam: Commonly co-administered with piperacillin to enhance spectrum via β-lactamase inhibition.
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