Q51

What is the mechanism of action of ketamine?

  • Antagonism of NMDA (subtype of glutamate) receptors
  • Inhibits reuptake of catecholamines and serotonin

Pass Criteria:

  • Bold to pass

What are its clinical effects?

  • Dissociative anaesthetics
  • Profound analgesia
  • Stimulate sympathetic nervous system
  • Bronchodilatation
  • Minimal respiratory depression
  • Stable CVS
  • Increased cerebral blood flow
  • Partial amnesia
  • Nystagmus

Pass Criteria:

  • Bold + 2

What are its adverse effects?
Prompt: Are there airway concerns?

  • Unpleasant emergence reaction (e.g. vivid dreams or hallucinations)
  • Laryngospasm
  • Increased salivation
  • Vomiting
  • Myoclonus

Pass Criteria:

  • Bold

Give an appropriate route and dose for procedural sedation in a 6 year old boy who sustained a laceration to the sole of his foot.
Prompt: Are there airway concerns?

  • 1-2 mg/kg IV, 4-10 mg/kg IMI

Pass Criteria:

  • Can state either IV or IM dose

Q52

What receptors do NA act on?

  • Predominantly a 1 receptor –> vascular smooth muscle constriction
  • Also a 2 receptor (presynaptic) – inhibits NA release (negative feedback)
  • Some effect on a 1 & 2 receptors (more potent effect on a 1)

Pass Criteria:

  • Need to mention predominant a 1 and one other receptor

How does NA increase blood pressure?
Prompt: What is the effect of NA on blood vessels?

  • a 1 activity –> vasoconstriction –> increased TPR –> increased DBP
  • a 1 –> increased myocardial contractility –> increased SBP
  • Overall rise in both DBP & SBP

Pass Criteria:

  • Bold

How does NA affect the heart rate?

  • a 1 activity increases heart rate
  • However compensatory baroreflex cause reflex bradycardia –> therefore minimal change in HR

Pass Criteria:

  • Bold

Q53

What is the mechanism of action of phenytoin?

  • Primarily Na+ channel blockade/reduced neuronal Na+ conductance and prolongation of inactivated state of Na+ channel
  • Reduces Ca2+ influx into cells and decreases glutamate release and enhances GABA release
  • Inhibit the generation of rapidly repetitive action potentials

Pass Criteria:

  • Bold

What are the risks associated with intravenous phenytoin administration?

  • Hypotension and bradycardia with rapid infusion (due to diluent)
  • Allergic reactions
  • Limit rate of infusion to maximum 50 mg/min (30-60 minutes)
  • Less likely with fosphenytoin
  • Local necrosis if extravasation

Pass Criteria:

  • Bold  to pass

Describe the elimination kinetics of phenytoin and why it is important clinically.

  • Dose-dependant elimination
  • First order elimination at low serum concentrations, however elimination becomes zero-order as concentration rises with prolongation of elimination half-life
  • Implication – small recurrent does increase may –> toxicity

Pass Criteria:

  • Explains concepts

What are the common features of acute overdose/intoxication with phenytoin?

  • Sedation
  • Coma
  • Nystagmus
  • Ataxia
  • Cerebellar toxicity
  • No cardiac toxicity with ingest overdoses of phenytoin

Pass Criteria:

  • 2 to pass

Q54

Describe the pharmacodynamics of amytriptyline.

Blocks reuptake of serotonin and noradrenaline, and blocks muscarinic, sympathetic alpha 1, GABA-A, Na+ channel and histamine receptors. There are various theories as to their mode of action; monoamine versus neurotrophic versus neuroendocrine theory.

Pass Criteria:

  • Bold and 2 other receptors to pass.

What are the toxic effects of amitryptyline and how are they mediated?

  • Blurred vision, dry mouth, tachycardia, urinary retention, delirium (anticholinergic effects)
  • Sedation (antihistamine effect)
  • Hypotension (anti-alpha effect)
  • Wide QRS and bradycardia (Na+ channel blockade)
  • Seizures (direct central effect)

Pass Criteria:

  • Must name effects and cause for at least three groups.

 


 

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