Thiopentone

BT_GS 1.30 Describe and compare the pharmacokinetics of intravenous induction agents …

BT_GS 1.31 Describe and compare the pharmacodynamics of intravenous induction agents …

Thiopentone is a terrific drug. Unfortunately, the current generation of trainees lack familiarity and confidence with it. 

T / F  compared with propofol, a standard induction dose of thiopentone causes less vasodilation and less hypotension

T / F  when diluted with 20 mL water, 500 mg thiopentone makes a 2.5% solution, with a pH of 11  (regarding the pH, can you explain why you think this is true or false? Why is this pH necessary / not necessary?)

T / F  in plasma, thiopentone is 80% bound to albumin

T / F  thiopentone is a weak base with pKa 7.6 – therefore, 12% of an injected dose will be available to cross the blood brain barrier

T / F  the majority of thiopentone is metabolised to inactive metabolites

T / F  thiopentone effectively blunts the upper airway reflexes

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Now that you’ve become fascinated by thiopentone, it would be useful to use this knowledge to answer some SAQ’s.

  1. Write short notes on the pharmacology of thiopentone.
  2. Compare and contrast the pharmacology of propofol and thiopentone.
  3. Explain the advantages and disadvantages of propofol and thiopentone for induction of general anaesthesia.

These 3 SAQ’s are in ascending order of complexity, in terms of the level of understanding they are testing. Regurgitating your summary notes (Q1) is low level knowledge – a candidate may score highly without really understanding what they are writing. But Q3 requires not only the application of PK and PD data – this information must be further organised to address the advantages and disadvantages. Scoring well on this question would demonstrate a high level of understanding (appropriate given the “core” nature of the drugs in question).

Have a go at answering the 3 SAQ’s above. While the 3 answers will each contain some of the same information, the final answers will be quite different. Hopefully this will help you reflect on the importance of reading the question!!

 

 

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