BT_GS 1.22 Describe the mechanisms of action and potential adverse effects of buffers, anti-oxidants, anti-microbial and solubilising agents added to drugs

T / F glycerol is part of the formulation of propofol – it is added as an emulsifying agent

T / F the intravenous formulation of paracetamol contains mannitol and povidone – both are to improve solubility

T / F amiodarone is formulated in alcohol and polysorbate 80 – these can cause hypotension with a rapid bolus

T / F phenytoin is soluble in water if the pH is < 3 – therefore hydrochloric acid is added to the ampoule

T / F sodium metabisulphite is added to some drugs ampoules as an anti-oxidant and anti-microbial – it is required to make morphine suitable for intrathecal use


  1. MacPherson R. Pharmaceutics and the anaesthetist. Anaesthesia, 2001; 56: 965-79
  2. MIMS and/or product info leaflets for each drug

BT_GS 1.19 Describe the mechanisms of drug interaction

Mechanisms of drug interaction can be classified as: pharmacodynamic, pharmacokinetic, and pharmaceutic.

T/F  the interaction between nitrous oxide and sevoflurane is an example of synergism because the combined effect is greater than would be predicted by simple addition

T/F  the interaction between propofol and remifentanil can be represented by a linear isobologram

T/F  in a patient using buprenorphine patches, morphine can have a reduced effect because buprenorphine is a partial antagonist

T/F  in a patient who has been reversed with neostigmine, but then needs to be urgently reintubated, suxamethonium would have a significantly reduced effect

T/F  cigarette smoking inhibits many of the cytochrome P450 enzymes, thereby slowing the metabolism of many drugs

T/F  competition for plasma protein binding sites between drugs, is a common reason for adverse drug effects in anaesthesia

T/F  if suxamethonium is injected into an IV port immediately after thiopentone, a precipitate will form in the line


Hemmings & Hopkins, Chapter 9 (Anesthetic drug interactions)


BT_GS 1.22 Describe the mechanisms of action and potential adverse effects of buffers, anti-oxidants, anti-microbial and solubilising agents added to drugs

There is one reference in the Primary Exam Reading List  which is a journal article not a book.  Pharmaceutics for the anaesthetist was written by a former Chair of the Primary Exam and contains material not available in the usual anaesthetic pharmacology textbooks (which is why it is still on the reading list even though it was published in 2001).

Interestingly, this article mentions cyclodextrins in the context of solubilising lipophilic drugs and 17 yrs later a cyclodextrin is a popular drug in anaesthetic practice but not in the way the article predicted.

T/F Water is considered a non-polar solvent

T/F Ethylene glycol is safe for use a solubilising agent

T/F 1 ml of oil emulsified in water results in a droplet surface area of approximately 500 m²

T/F Lyophilisation is used to prevent hydrolytic degradation of drugs

T/F Trace amounts of oxygen in an ampoule can be enough to initiate the oxidation process

T/F Propofol has anti-oxidant properties

T/F Hydrolysis, oxidation, isomerisation and exposure to ultraviolet light can reduce the potency of drugs

T/F Preservatives are substances added to pharmaceutical products to prevent degradation

T/F Hypotonic and hypertonic solutions can cause pain on injection, thrombophlebitis, haemolysis

T/F Intrathecal use of preservative containing drugs is strongly associated with neurotoxicity

T/F pH adjustment of drug preparations is done for many reasons which can be difficult to determine


How is drug X presented?  This is a old favourite in the vivas and definitely reveals those candidates who have used drug X and those who haven’t.  There is no specific LO today but a post next week will cover BT_GS 1.22.

The questions in today’s post are not true/false and there is no specific reference.  I expect you should be able to find the answers from simple observation, experimentation, consultation with your consultants or from the product information leaflets*.

*Ask your anaesthetic assistant or the pharmacist in your hospital.

Do you know the difference between a vial and an ampoule?  Where does a ‘minim’ fit in?  (hint: ‘eyes’)

Which drugs require reconstitution?  Which drug is more soluble: parecoxib or cefazolin?

What are the contents of an ampoule of:

  • propofol?
  • thiopentone?
  • local anaesthetics for intrathecal administration? What is NOT in these ampoules?

What happens in the injection port if you inject suxamethonium straight after thiopentone?*  Are there any other combination of drugs which have the same effect?

*Not really examinable in the Primary Exam but an important point for practice

Which drugs are dangerous if a whole ampoule is administered and for which would this be annoying but not life threatening?