Pharmacology Lecture 7: Drug Action
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Questions and Answers

What is the primary mechanism of action of beta blockers?

Competitive inhibition of beta receptors in the heart, thereby reducing heart rate and contractility.

How do alpha-2 agonists decrease blood pressure?

By stimulating alpha-2 receptors in the brain, which activates the parasympathetic nervous system, leading to decreased sympathetic tone and reduced blood pressure.

What is the mechanism of action of ACE inhibitors?

ACE inhibitors block the conversion of angiotensin I to angiotensin II, a potent vasoconstrictor, thereby reducing blood pressure.

How do calcium channel blockers reduce blood pressure?

<p>By blocking the influx of calcium ions into vascular smooth muscle cells, leading to relaxation of blood vessels and decreased blood pressure.</p> Signup and view all the answers

What is the primary effect of adrenergic neurotransmitters on the heart?

<p>Increasing heart rate, contractility, and conduction velocity through stimulation of beta-1 receptors.</p> Signup and view all the answers

What is the mechanism of action of penicillins?

<p>inhibiting cell wall synthesis</p> Signup and view all the answers

How do tetracyclines inhibit protein synthesis?

<p>by inhibiting aa-tRNA binding to the A site</p> Signup and view all the answers

What is the common core structure of cell wall synthesis inhibitors?

<p>B-Lactam</p> Signup and view all the answers

What are three possible mechanisms of penicillin resistance?

<p>alterations at PBPs, prevention of B-lactams from accessing PBPs, and expression of B-lactamase</p> Signup and view all the answers

What class of antibiotics inhibits protein synthesis?

<p>Aminoglycosides, tetracyclines, amphenicols, and macrolides</p> Signup and view all the answers

What is the difference between penicillins and cephalosporins?

<p>Differences in antibacterial specificity explained by interactions with various penicillin binding proteins in bacteria</p> Signup and view all the answers

What are the pharmacokinetic characteristics of penicillins?

<p>Acid stability varies, lipid insoluble, do not enter mammalian cells, cross blood/brain barrier only if meninges are inflamed, and most penicillins are eliminated renally</p> Signup and view all the answers

What is a common adverse reaction to penicillins?

<p>Type 1&amp;2 sensitivity reactions</p> Signup and view all the answers

What is the possibility of experiencing Candidiasis with prolonged use of antibiotics?

<p>Candidiasis occurs with prolonged use</p> Signup and view all the answers

What is the unique characteristic of 5th generation cephalosporins?

<p>Expanded G+, including MRSA, with high affinity binding</p> Signup and view all the answers

How are most cephalosporins administered and excreted?

<p>Mostly administered parenterally, and excreted through renal tubular secretion</p> Signup and view all the answers

What is the main reason for cross-reactivity between penicillins and cephalosporins?

<p>Similarity of sidechains between 1&amp;2 gen ceph and penicillins</p> Signup and view all the answers

What is the primary mechanism of action of aminoglycosides in bacterial protein synthesis?

<p>Inhibition of initiation, causing mRNA misreading</p> Signup and view all the answers

What is the effect of tetracyclines on bacterial protein synthesis?

<p>Inhibition of tRNA binding</p> Signup and view all the answers

What is the adverse effect of aminoglycosides on the kidneys?

<p>Nephrotoxicity, accumulation in proximal tubular cells</p> Signup and view all the answers

What is the consequence of prolonged use of tetracyclines on teeth?

<p>Accumulation in teeth, leading to discoloration</p> Signup and view all the answers

Study Notes

Mechanisms of Action

  • Penicillins inhibit cell wall synthesis
  • Tetracyclines inhibit protein synthesis at tRNA by inhibiting aa-tRNA binding to A site

Cell Wall Synthesis Inhibitors

  • Penicillins and cephalosporins are examples of cell wall synthesis inhibitors
  • These inhibitors have a common core structure: B-Lactam

Penicillin Resistance

  • Alterations at PBPs cause a decrease in drug binding ability at the protein, decreasing antibacterial activity
  • Prevention of B-lactams from accessing and entering pore channels and reaching PBPs in the cell membrane of Gram-negative bacteria
  • Expression of B-lactamase in certain bacteria

Protein Synthesis Inhibitors

  • Aminoglycosides, tetracyclines, amphenicols, and macrolides are examples of protein synthesis inhibitors
  • These inhibitors target different stages of bacterial protein synthesis

B-Lactams

  • Penicillins and cephalosporins are examples of B-Lactams
  • Amoxicillin is a synthetic, broad-spectrum penicillin with no B-lactamase resistance
  • Clavulanic acid is a synthetic B-lactamase inhibitor

Penicillin Pharmacokinetics

  • Acid stability varies among penicillins
  • Lipid insoluble, do not enter mammalian cells
  • Cross the blood-brain barrier only if meninges are inflamed
  • Most penicillins are eliminated renally very quickly

Penicillin ADR

  • Opening the B-lactam ring forms benzylpenicilloyl
  • Type 1 & 2 sensitivity reactions
  • Superinfection (e.g. Candidiasis) occurs with prolonged use

Cephalosporins

  • 5th generation cephalosporins have expanded Gram-positive, including MRSA, and common Gram-negative coverage
  • Binding with high affinity (ceftaroline)

Cephalosporin Pharmacokinetics

  • Acid stable
  • Most administered parenterally, with few orally
  • Distribution: extracellular fluid, some cross blood-brain barrier to treat meningitis
  • Excreted mostly through renal tubular secretion

Cephalosporin ADR

  • Similar to penicillins
  • Cross reactivity between penicillins and cephalosporins causes ADR
  • Opening the B-lactam ring forms cephalosporoyl

Bacterial Protein Synthesis

  • Initiation
  • tRNA binding
  • Peptide bond formation
  • Translocation
  • Elongation cycle

Bacterial Protein Synthesis Inhibitors

  • Inhibit one of the four key steps in bacterial protein synthesis
  • Most are bacteriostatic, except aminoglycosides which are bactericidal

Aminoglycosides

  • Inhibit initiation
  • MOA: [30s] inhibit codon-anticodon interaction, causing mRNA misreading

Tetracyclines

  • Inhibit tRNA binding
  • MOA: [30s] inhibit aa-tRNA binding to A site

Amphenicols

  • Inhibit transpeptidation
  • MOA: [50s] inhibit peptide bond formation

Antibacterial Macrolides

  • Inhibit elongation and/or translocation
  • MOA: [50s] prevent transfer of tRNA with the growing peptide from A site to P site

Bacterial PSIs: Aminoglycosides

  • Bactericidal
  • Active against Gram-positive and Gram-negative bacteria
  • Time and concentration dependent, with AUC:MIC
  • Pharmacokinetics: administered intramuscularly or intravenously, eliminated through glomerular filtration
  • Ototoxicity: hearing loss and impaired vestibular function
  • Nephrotoxicity: accumulation in proximal tubular cells

Bacterial PSIs - Tetracyclines

  • Broad spectrum, active against Gram-positive and Gram-negative bacteria
  • Bacteriostatic
  • Generally administered orally, but also parenterally
  • GI disturbance: direct irritation and modulation of gut flora with prolonged use
  • Ca chelation: accumulation in teeth and bones

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