Q61

Describe the pharmacodynamics of propranolol that make it useful in thyrotoxicosis.
Prompt: What are the cardiovascular effects?

  • B-blocker – competitive non selective antagonist of both B1 and B2 receptors
  • CVS effects:
    • Decreased BP
    • Decreased HR (especially rate control of AF)
    • Both negatively inotropic and chronotropic
    • Decreased catecholamine effects which are prominent in hyperthyroidism
  • Inhibition of perihperial conversion of thyroxine (T4) to triiodothyronine (T3) – this is especially evident with propranolol compared with other B-blockers
  • Has Na-channel blocking action (‘membrane stabilisation‘)

Pass Criteria:

  • Bold and 2 CVS effects to pass.

What are the adverse effects of propranolol?

  • CVS – bradycardia, hypotension, worsening of CCF, worsening ischaemia in PVD, QRS widening and arrythmias in toxicity
  • CNS – sedation, depression, dreams, coma/seizure/delirium in toxic doses
  • Respiratory – worsening asthma/COPD
  • Other – decreased exercise tolerance, fatigue, impotence, decreased libido, masks symptoms of hypoglycaemia

Pass Criteria:

  • 1 example from each bold system to pass.

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