Questions and Answers
Which factor contributes to the instability of the β-lactam ring in penicillins?
What role does the carboxylate ion play in the action of penicillins?
What is a primary reason for the varied susceptibility of bacterial strains to penicillin?
Why does penicillin have good activity against Gram-positive bacteria?
Signup and view all the answers
How does the structure of the acylamino side chain impact penicillin's effectiveness?
Signup and view all the answers
Which mechanism serves as a physical barrier that penicillin must overcome in Gram-negative bacteria?
Signup and view all the answers
What effect does the presence of efflux pumps in Gram-negative bacteria have on penicillin?
Signup and view all the answers
What is the significance of PBP mutations in bacterial resistance to penicillin?
Signup and view all the answers
Which component is NOT part of the penicillin structure?
Signup and view all the answers
What type of amino acids are predominantly found in human biochemistry?
Signup and view all the answers
Which sugars form the backbone of the bacterial cell wall?
Signup and view all the answers
What is the role of transpeptidase enzymes in bacterial cell walls?
Signup and view all the answers
What distinguishes the penam derivatives in terms of structure?
Signup and view all the answers
Which of the following best describes the peptide chains in bacterial cell walls?
Signup and view all the answers
What is the significance of the D-alanine displacement during peptide chain linking?
Signup and view all the answers
How do bacteria utilize racemase enzymes regarding amino acids?
Signup and view all the answers
What is the primary reason penicillin G is not effective when taken orally?
Signup and view all the answers
What effect can high doses of procaine penicillin have?
Signup and view all the answers
Which of the following statements about penicillin G procaine is true?
Signup and view all the answers
What is a consequence of the ring strain in penicillin G?
Signup and view all the answers
What is the main action of benzathine in penicillin G benzathine?
Signup and view all the answers
What factor enhances the passage of certain penicillins through the Gram-negative bacterial outer membrane?
Signup and view all the answers
Which type of allergic reaction can penicillins cause?
Signup and view all the answers
What role does procaine play in procaine penicillin?
Signup and view all the answers
Which of the following is classified as a broad-spectrum antibiotic?
Signup and view all the answers
How does the introduction of an ionized or polar group into the α-position of penicillin G's side chain affect its activity?
Signup and view all the answers
What limitation does penicillin exhibit due to β-lactamase sensitivity?
Signup and view all the answers
What is a common challenge associated with the oral absorption of Ampicillin?
Signup and view all the answers
Amoxicillin is said to have better oral absorption than Ampicillin primarily because:
Signup and view all the answers
What is the primary reason simple methyl esters are not used as prodrugs for penicillins?
Signup and view all the answers
Which of the following statements is true regarding ticarcillin?
Signup and view all the answers
Which of the following modifications improves the oral activity of Ampicillin?
Signup and view all the answers
What is a key characteristic that distinguishes ureidopenicillins from carboxypenicillins?
Signup and view all the answers
What type of antibiotic class do Amoxicillin, Carboxypenicillins, and Ureidopenicillins represent?
Signup and view all the answers
Why must ticarcillin be administered parenterally?
Signup and view all the answers
What advantage do ureidopenicillins have over carboxypenicillins?
Signup and view all the answers
What is the effect of administering tazobactam with piperacillin?
Signup and view all the answers
What is the relationship between aryl esters and β-lactam rings in the context of extended esters?
Signup and view all the answers
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.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
Test your knowledge on the non-classical β-lactams, including carbapenems and monobactams. This quiz covers their structures, functions, and comparisons with classical antibiotics like penicillins. Explore the critical aspects of these antibiotics in a concise format.