Questions and Answers
Which of the following are natural products of tetracyclines?
Which of the following tetracyclines is the most widely used?
What is the mechanism of action of tetracyclines?
Bacteriostatic; reversibly binds 30S subunit of bacterial ribosomes, blocking protein synthesis.
How are tetracyclines primarily excreted?
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What is true about doxycycline's bioavailability?
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Doxycycline is indicated for treatment of _____ disease.
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Which tetracycline is especially effective in treating acne?
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Match the following tetracycline products with their types:
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Tetracyclines are effective against resistant gonococci.
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What are the adverse effects associated with tetracyclines?
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What is the excretion process for aminoglycosides?
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What is the typical plasma half-life of aminoglycosides?
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What should be adjusted in renal dysfunction when using aminoglycosides?
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What spectrum do aminoglycosides primarily cover?
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Study Notes
Overview of Antibiotic Classes
- Major antibiotic classes include Tetracyclines, Aminoglycosides, and Macrolides.
Tetracyclines: Natural Products
- Natural products: oxytetracycline and demeclocycline produced by Streptomyces species.
Tetracyclines: Semisynthetic Products
- Semisynthetic variants include tetracycline, doxycycline, and methacycline.
Tetracyclines: Mechanism of Action
- Exhibit bacteriostatic activity by reversibly binding to the 30S ribosomal subunit, inhibiting protein synthesis.
- Block the binding of amino-acyl tRNA.
- Resistance occurs via TetA protein facilitating Mg-dependent drug efflux and ribosomal binding alterations.
- Drugs gain entry through passive diffusion and active transport mechanisms.
Tetracyclines: Pharmacokinetics
- Oral (PO) absorption is incomplete, negatively affected by di/trivalent ions and dairy products.
- Wide distribution, crossing blood-brain barrier (25%), and present in fetal and milk/nursing tissues (50-60%).
- Excretion mainly via kidneys, unchanged in urine; levels rise in renal failure.
Doxycycline: Pharmacokinetics
- Almost complete PO bioavailability; food and dairy minimally affect absorption unlike metal ions (e.g., iron).
- Long half-life allows for once daily or BID dosing.
- Excreted primarily through bile into feces, does not accumulate in renal insufficiency, no dosage adjustment required.
Doxycycline: Clinical Indications
- Effective against infections from Chlamydia trachomatis, anthrax, cholera, Lyme disease, and Rocky Mountain spotted fever.
- Combined with cephalosporin to target anaerobic bacteria.
Minocycline: Pharmacokinetics
- Most lipid-soluble tetracycline with 100% PO bioavailability.
- High CNS distribution and longest half-life among tetracyclines.
- Undergoes significant metabolism; excretes predominantly as metabolites in urine and feces.
Minocycline: Clinical Indications
- Particularly effective for acne treatment (Propionibacterium acnes) due to enhanced skin penetration.
- Used to control meningococcal carrier states with a 200 mg PO regimen over 5 days.
Tetracyclines: Spectrum
- Gram-positive: Susceptible to certain staphylococci and streptococci, but alternatives often preferred due to increased resistance.
- Effective against Propionibacterium acnes and certain Gram-negative bacteria, including H. influenzae and K. pneumoniae.
- Indications include Rickettsiae, Mycoplasma pneumonia, Chlamydia trachomatis, and Helicobacter pylori.
- Not effective against resistant Gonococci.
Tetracyclines: Adverse Drug Reactions (ADRs)
- Common GI effects include distress, heartburn, and potential esophageal ulcers.
- Phototoxicity risks, particularly with demeclocycline and doxycycline.
- Skeletal adverse effects due to chelation with teeth and bones; contraindicated in children.
Aminoglycosides: Pharmacokinetics
- Water-soluble and polar, poorly absorbed orally; significant remaining in the GI tract post-administration.
- Minimal CNS penetration; concentrates in renal cortex and ear structures.
- Half-life ranges from 2 to 3 hours with low plasma protein binding at 10%.
- Excretion primarily through urine, necessitating dosage adjustments in renal dysfunction.
Aminoglycosides: Once Daily Dosing
- Concentration-dependent bactericidal effect with a notable post-antibiotic effect.
- Toxicity is both time- and concentration-dependent; exceeding toxicity thresholds impacts duration of exposure.
- Smaller, multiple doses reduce toxicity risk compared to fewer larger doses.
Aminoglycosides: Spectrum
- Limited effectiveness against Gram-positive bacteria, primarily Staphylococcus over Streptococcus due to rising resistance.
- Commonly used with penicillins or cephalosporins for treating serious staphylococcal infections.
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Description
This quiz explores the major classes of antibiotics with a focus on Tetracyclines. It covers their natural and semisynthetic products, mechanisms of action, pharmacokinetics, and resistance mechanisms. Test your knowledge on how these antibiotics work and their clinical implications.
