Q31

Define drug elimination half life.

PROMPT – Is there a formula you can use?

  • Time required to change the amount of drug in the body by 1/2 during elimination
  • T1/2 = 0.7 x Vd/clearance (0.7 approx log 2)
  • 50% after 1, >90% after 4

Pass Criteria:

  • Bold to pass

How does knowledge of a drug's half life help us clinically?

  • Dosing regimens
  • Decay afterdose/overdose
  • Time to steady state after dose change

Pass Criteria:

  • 2 to pass

What disease states can affect elimination half-life?

  • Liver
  • Renal
  • Cardiac disease

Pass Criteria:

  • One organ

What disease state could affect the elimination half-life of morphine?

  • Liver
  • Renal

Pass Criteria:

  • One organ

 

Q32

Outline the mechanism of action for aspirin.

  • Irreversible non-selective cyclooxygenase inhibition (COX 1 and 2) resulting in
    • In platelets, irreversible inhibition of COX 1 results in reduction in thromboxane A2 and inhibition of platelet aggregation for the life of the platelet (10 days).
    • In tissues, inhibits prostaglandin synthesis (COX 2). Results in anti-inflammatory action, analgesic and anti-pyretic effects.

Pass Criteria:

  • Bold to pass
  • Need to mention platelet effect (COX 1) and tissue (COX 2) anti-inflammatory or analgesic effect

Describe the pharmacokinetics of aspirin.

  • Rapidly absorbed from stomach and intestine, aspirin hydrolysed to salicyclic acid in plasma and blood, peak plasma level within 1-2 hours.
  • Serum half-life of aspirin 15 minutes, low protein binding, saturable metabolism with increasing doses (switches from first to zero order metabolism). Urinary alkalinisation increases excretion of salicylate and its conjugates.

Pass Criteria:

  • Bold + 2

Outline the adverse effects of aspirin.

  • GI upset
  • Gastrointestinal bleeding from gastritis or peptic ulceration
  • Hepatotoxicity
  • Hypersensitivity reactions (asthma, angioedema, rash)
  • Prolonged bleeding time from platelet inhibition

Pass Criteria:

  • Bold + 1 other

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