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Questions and Answers
What is the primary adverse effect associated with high doses of penicillins?
Which of the following penicillins is associated with nephrotoxicity?
What is a key characteristic of the 1st generation cephalosporins?
Which combination of penicillin and β lactamase inhibitor is correctly matched?
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What adverse effect can benzathine penicillin cause at the injection site?
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Which microorganisms are classified as β lactamase producing bacteria?
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What is the treatment for superinfection caused by Clostridium difficile after penicillin therapy?
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Which of the following drugs is considered a broad-spectrum beta-lactam antibiotic that can pass the blood-brain barrier?
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What is the primary mechanism of action of the antibiotic Aztreonam?
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Which adverse effect is most commonly associated with the use of Vancomycin?
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What mechanism allows bacteria to resist the effects of penicillins?
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In which situation would Vancomycin be indicated for use?
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Which type of penicillin is effective against both gram-positive cocci and certain gram-negative cocci?
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Which condition is NOT typically treated with penicillins?
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What distinguishes Meropenem from Imipenem?
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Which statement about Ertapenem is true?
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What is a common adverse effect associated with the use of penicillins?
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In patients with a history of penicillin allergy, which medication can potentially cause a similar allergic reaction?
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What is the recommended approach to prevent hypersensitivity reactions to penicillins?
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Which of the following is NOT a symptom of penicillin-induced hypersensitivity?
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What severe reaction can occur after the first dose of penicillin in patients with syphilis?
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Study Notes
Penicillins
- Penicillins are antibiotics that inhibit bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs).
- Bacteria can develop resistance to penicillins through various mechanisms, including:
- Synthesis of β-Lactamase enzymes that destroy the β-lactam ring of penicillins
- Alteration in the binding site of PBPs
- Decreased permeability (influx) to penicillins
- Increased efflux of the antibiotic from the inside of the bacterial cells to the outside
- Penicillins are classified based on their spectrum of activity:
- Narrow-spectrum penicillins: Active against Gram-positive bacteria (cocci and bacilli), Gram-negative cocci, anaerobes (except β-lactamase-producing Bacteroides fragilis), Spirochaetes (Treponema pallidum), and Actinomyces Israeli
- Broad-spectrum penicillins: Active against the same organisms as narrow-spectrum penicillins, plus Gram-negative bacilli (except Pseudomonas, Proteus, and Klebsiella)
- Extended-spectrum penicillins: Active against the same organisms as broad-spectrum penicillins, plus Pseudomonas, Proteus, and Klebsiella
- Penicillins are used for:
- Chemoprophylaxis in rheumatic fever and endocarditis
- Treatment of respiratory tract infections, urinary tract infections, gastrointestinal infections (typhoid fever, eradication of H. pylori in peptic ulcer), meningitis, gonorrhea, pyogenic infections (abscess, osteomyelitis), endocarditis, diphtheria, tetanus, gas gangrene, anthrax, and Actinomycosis
- Penicillins can cause adverse effects, including:
- Hypersensitivity (allergic reactions) due to penicilloic acid acting as a hapten, manifested as rash, urticaria, angioedema, or anaphylactic shock
- Jarisch-Herxheimer reaction due to the release of toxins from dead Treponema in syphilitic patients treated with the first dose of penicillin, with manifestations similar to allergic reactions
- Diarrhea and superinfection caused by monilia (candida) or endotoxin of Staph. or Clostridium difficile
- Seizures and epileptic fits in case of large doses or intrathecal injection
- Hypernatremia or hyperkalemia due to the use of Na+ or K+ salts
- Local pain and induration after IM injection and thrombophlebitis after IV injection with benzathine penicillin
- Platelet dysfunction caused by carboxy penicillin
- Nephrotoxicity caused by methicillin
β-Lactamase Producing Bacteria
- β-Lactamase producing bacteria are PEPSI organisms (Proteus, E. coli, Pseudomonas, Staph, H. Influenza)
- All generations of penicillins are β-Lactamase sensitive except the Oxa group
- Some generations of penicillins can overcome β-Lactamase by combinations with β-Lactamase inhibitors
- β-Lactamase inhibitors (Sulbactam, clavulanic acid, and Tazobactam) are combined with penicillin derivatives to form:
- Unasyn (Ampicillin + Sulbactam)
- Augmentin and Hibiotic (Amoxycillin + Clavulanic acid)
- Tazocin (Piperacillin + Tazobactam)
Cephalosporins
- Cephalosporins are β-lactam antibiotics similar to penicillin in structure and mechanism of action
- Cephalosporins are classified into generations based on their spectrum of activity and resistance to β-lactamases:
- 1st Generation: Broad-spectrum, more active against Gram-positive than Gram-negative bacteria, resistant to β-lactamases, cannot cross the blood-brain barrier (BBB), administered orally (Cephalexin, Cephradine) or parenterally (Cefazolin, Cefapirin)
- 2nd Generation: Broad-spectrum, more active against Gram-negative than Gram-positive bacteria, more resistant to β-lactamases than 1st generation, cannot cross the BBB except for Cefuroxime, administered orally (Cefuroxime, Cefaclor) or parenterally (Cefuroxime, Cefamandole, Cefoxitin)
- 3rd Generation: Broad-spectrum, more active against Gram-negative than Gram-positive bacteria, more resistant to β-lactamases than 2nd generation, cross the BBB except for Cefoperazone, administered orally (Cefixime) or parenterally (Cefotaxime, Ceftriaxone)
- 3rd generation cephalosporins have a very wide spectrum, active on Gram-positive, Gram-negative, aerobes, and anaerobes, growing or not.
- Indications for 3rd generation cephalosporins include serious hospital-acquired (nosocomial) infections.
- Adverse effects of cephalosporins include allergy (partial cross-allergy with penicillin), gastrointestinal disturbances, and seizures.
Carbapenems
- Carbapenems are β-lactam antibiotics with a broad spectrum of activity.
- Meropenem is a carbapenem similar to imipenem but is not metabolized by dihydropeptidase enzyme and rarely produces seizures.
- Ertapenem is similar to meropenem but has a longer half-life and is administered parenterally once daily.
Monobactams
- Monobactams are synthetic β-lactam antibiotics.
- Aztreonam is a monobactam that is bactericidal, inhibiting cell wall synthesis (PBP3).
- Aztreonam is active against Gram-negative bacteria only (including Pseudomonas), inactive against Gram-positive and anaerobic bacteria.
- Indications for Aztreonam include patients allergic to penicillins (no cross-allergy with penicillin).
- Adverse effects of Aztreonam include gastrointestinal disturbance.
Vancomycin
- Vancomycin is a natural antibiotic not absorbed orally but is given orally to act locally on the GIT, given by IV infusion to treat systemic infection.
- Vancomycin poorly penetrates the BBB, except in meningitis, and is excreted unchanged in urine.
- Vancomycin is bactericidal, inhibiting cell wall synthesis.
- Spectrum of activity includes Gram-positive bacteria (including MRSA, Clostridium difficile, and Enterococci).
- Vancomycin is used for:
- Chemoprophylaxis against endocarditis in penicillin-allergic patients
- Treatment of pseudomembranous colitis (given orally)
- Treatment of MRSA infections (given IV infusion)
- Urinary tract infections (UTIs)
- Adverse effects of Vancomycin include:
- Ototoxicity
- Nephrotoxicity
- Red man syndrome (rapid IV infusion), which causes vasodilation of cutaneous blood vessels and flushing, leading to shock.
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Description
This quiz explores the mechanisms of action and resistance of penicillins, a vital class of antibiotics. It covers their spectrum of activity, including narrow- and broad-spectrum types, and the various bacterial adaptations that can lead to resistance. Test your knowledge on this essential topic in microbiology.
