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4 - Pharmacology

Simon Bricker
Affiliation:
Countess of Chester Hospital
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Summary

Chirality

Commentary

The science of chirality is somewhat indigestible, and you might feel aggrieved were this to be the only pharmacology that you were given the opportunity to discuss in the exam. The introduction of levobupivacaine and ropicaine, however, has given this subject some topical relevance and, so even if you cannot unravel the nomenclature convincingly, you will have to be prepared to talk about drugs which can be presented as pure enantiomers. (If you are struggling for facts it may help if you remember that in the case of the newer drugs, ‘R’ stands for ‘risky’ and ‘S’ stands for ‘safe’.)

The viva

The subject may be introduced by a discussion of drugs that are chiral, in particular local anaesthetics. Drugs such as bupivacaine and prilocaine are racemic mixtures which contain equal numbers of isomers or enantiomers (see below). The improved safety profile of single enantiomer preparations has given chirality more immediate anaesthetic relevance.

  • Bupivacaine: the S(−) enantiomer has less affinity for, and dissociates quicker from, myocardial sodium channels. The risk of cardiovascular and CNS toxicity is reduced. The S(−) enantiomer also exerts some vasoconstrictor activity.

  • Ropivacaine: this is the pure S(−) enantiomer of propivacaine. It also has a safer cardiovascular profile in overdose.

  • Prilocaine: the S(+) enantiomer is a stronger vasoconstrictor and is metabolized more slowly than the R(−) form which therefore produces higher concentrations of o-toluidine and a greater risk of methaemoglobinaemia.

  • Lidocaine (lignocaine): this is achiral.

You will then be asked in more detail about chirality and isomerism.

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Publisher: Cambridge University Press
Print publication year: 2008

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References

Myles, PSet al. (2007). Avoidance of nitrous oxide for patients undergoing major surgery: a randomized controlled trial. Anesthesiology, 107(2), 221–31.
Mangano, DTet al. (1996). Effect of atenolol on mortality and cardiovascular morbidity after noncardiac surgery. New England Journal of Medicine, 335, 1713–20.

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  • Pharmacology
  • Simon Bricker
  • Book: The Anaesthesia Science Viva Book
  • Online publication: 08 August 2009
  • Chapter DOI: https://doi.org/10.1017/CBO9780511544507.006
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  • Pharmacology
  • Simon Bricker
  • Book: The Anaesthesia Science Viva Book
  • Online publication: 08 August 2009
  • Chapter DOI: https://doi.org/10.1017/CBO9780511544507.006
Available formats
×

Send book to Google Drive

To send content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about sending content to Google Drive.

  • Pharmacology
  • Simon Bricker
  • Book: The Anaesthesia Science Viva Book
  • Online publication: 08 August 2009
  • Chapter DOI: https://doi.org/10.1017/CBO9780511544507.006
Available formats
×