Drug Metabolism

BT_GS 1.11  Describe the mechanisms of hepatic and non-hepatic metabolism of drugs….


T / F   a phase 1 reaction exposes a polar group on the parent molecule, rendering it more water soluble

T / F  all phase 1 reactions are catalysed by the CYP450 enzymes

T / F  adding (conjugating) glucuronide to the parent molecule is an example of a phase 2 reaction

T / F  phase 2 reactions decrease the activity of the parent compound

T / F  CYP2D6 metabolises codeine to morphine – this enzyme is absent in 1% of caucasians


Is pharmacogenetic testing the “new frontier” of pharmacology? Your patients might have seen websites like this one from the Mayo clinic. Some patients are already coming to hospital with their “genetic printout” stating which drugs they should have!

IV Fluids – Albumex

IT_GS 1.5   Describe the chemical composition of crystalloids and colloids used in clinical practice and their effects when used in volume replacement

stiff peaks2

The word albumin is derived from the Latin albus, meaning “white” (in reference to the white of an egg). Albumin is the most abundant egg white protein (although it’s ovalbumin – not quite the same as human serum albumin). Ever wondered why you can get “stiff peaks” to form when you beat egg whites? Click here to find out.

T / F   “Albumex 4” contains 4 g/L of albumin

T / F   Albumex is not a human blood product, because it is manufactured by recombinant DNA techniques

T / F   Albumex contains 150 mmol/L Na+ and 150 mmol/L Cl-

T / F   Albumex is rendered free of possible virus transmission by pasteurisation (heating to 60 degrees C for 10 hours)

T / F   the half life of albumin in the circulation is 48 hours

BT_GS 1.16 Describe alterations to drug response due to ageing

It is uncommon these days for me to have a day where I don’t anaesthetise at least one older patient. Approximately 15% of the Australian population is aged over 65. There are currently almost half a million Australians aged over 85 yrs of age and this number is expected to double in the next 20 yrs !


This elderly person (Fauja Singh) is a fairly amazing older person, completing a marathon aged 100!

Chronological age does not necessarily correspond to physiological age, but there are certain changes which occur fairly consistently with increasing age.  Acute Pain Management: scientific evidence (10.2.3 in case the link doesn’t work) has summary of the changes that occur with ageing and significance for drug dosing.

BT_GS 1.16 Describe alterations to drug response due to physiological change with particular reference to the elderly

A given bolus dose of propofol in an elderly person, compared with a 40yr old, will have an increased effect due to the decreased size of the central compartment   TRUE/FALSE

Changes in cardiac output in the elderly generally slow the rate of induction with volatile anaesthetic agents    TRUE/FALSE

GFR decreases by about 10% per decade after 50 yrs of age   TRUE/FASLE

Oral bioavailability of some drugs may be increased in the elderly due to a reduction in both liver blood flow and metabolic capacity    TRUE/FALSE

Both albumin and alpha1 acid glycoprotein levels fall equally in the elderly, increasing the free fraction of highly protein bound drugs   TRUE/FALSE





BT_PM 1.17 Pharmacokinetics of intravenous opioids and clinical relevance

I am not a massive fan on memorising a whole lot of numbers for the sake of it – boring!!

However, sometimes these pesky numbers can actually help us guide clinical practice and, in that situation, they take on a whole new level of relevance. The pharmacokinetics of opioids are a case in point.


Hopefully no opioids in this handbag (although to be honest, I couldn’t be sure) Cottesloe, WA

BT_PM 1.17 Describe the pharmacokinetics of intravenous opioids and their clinical applications

The high lipid solubility of fentanyl confers a long duration of action when given intrathecally  TRUE/FALSE

The rapid speed on onset of alfentanil is primarily due to its low pKa  TRUE/FALSE

Duration of action of remifentanil is determined by its elimination half life   TRUE/FALSE

The terminal elimination half life of morphine and fentanyl is similar   TRUE/FALSE

Active metabolites of both morphine and pethidine contribute to the duration of analgesic effect   TRUE/FALSE

Nitrous Oxide

BT_GS 1.27 Describe the pharmacology of nitrous oxide


T / F   nitrous oxide does not support combustion

T / F   nitrous oxide acts synergistically with volatile agents to produce anaesthesia

T / F   nitrous oxide does not cause any peripheral vasodilation

T / F   nitrous oxide acts on GABA receptors in the brain

T / F   nitrous oxide use is associated with post-operative MI

Serotonin Syndrome

BT_PO 1.102 Discuss the clinical features and management of serotonin syndrome


T / F   all serotonin receptors are ligand gated ion channels

T / F   tramadol, pethidine, fluoxetine, amphetamines and amitriptyline are all potentially serotonergic

T / F   monoamine oxidase inhibitors are not serotonergic

T / F   features of serotonin syndrome include: CNS excitation; hyperthermia; and hyper-reflexia

T / F   treatment is usually supportive, although cyproheptadine is a potential antidote

SS_PA 1.52 Pharmacokinetic differences in  neonates and children compared with adults and the implications for anaesthesia

A little person I know had an anaesthetic last week having swallowed a curtain hook, probably a couple of months ago. He had not been very keen to eat solid food!!

SS_PA 1.52 Describe how the pharmacokinetics of drugs commonly used in anaesthesia in neonates and children differ from adults and the implications for anaesthesia

Water soluble drugs have a larger volume of distribution in neonates TRUE/FALSE

Drugs that depend on redistribution into fat compartments for their termination of action have longer durations of action in neonates    TRUE/FALSE

The absorption of oral drugs is more rapid in neonates compared with adults   TRUE/FALSE

The relationship between weight and drug elimination is linear in children  TRUE/FALSE

Remifentanil’s half life is unchanged in neonates    TRUE/FALSE

BT_GS 1.12 Context sensitive half time

A topical area for us as we often run intra-operative infusions of drugs, sometimes for quite long periods of time!

The topic is not brilliantly covered in that many books. Pharmacology and Physiology for Anaesthesia Ch 2 by Hemmings and Egan, is a great chapter full stop and does discuss the topic. This article in BJA Education also gives a good little summary.


Another photo from beautiful Tasmania today, Wineglass Bay

The context sensitive half time of a drug will never be longer than its elimination half life   TRUE/FALSE

The “context” is the duration of the infusion   TRUE/FALSE

Following cessation an infusion, the fall in plasma concentration is proportional to elimination of drug from the body  TRUE/FALSE

Prolongation of the half time, as the duration of the infusion increases, is directly proportional to the lipid solubility of the drug  TRUE/FALSE

Context sensitive half time is a term that only applies to multi compartmental models   TRUE/FALSE

BT_GS 1.21 Isomers

I think isomerism is a very cool little trick of nature! How amazing to think that one chemical structure can have such different properties due to the orientation of the same atoms on a single carbon, and also that our bodies are able to recognise these differentially.

We sometimes talk about enantiomers as being non superimposable mirror images of each other, which made me think of mirror twins ( apologies for the high class nature of the “journal” I took this from! However, if you are interested in twins, these episodes of Insight from SBS may interest you)


No photos of mirrors today, just this (not perfect) reflection of Cradle Mountain in Dove Lake, Tasmania. One of my favourite parts of the world. I have seen the lake surface truly glass like, but do not have an image of it to share with you.

BT_GS 1.21 Describe and give examples of the clinical importance of isomerism

Ketamine, propofol and bupivacaine are all presented as racemic mixtures for use in Australia TRUE/FALSE

The D isomer of amphetamine is more potent as a CNS stimulant than the L isomer TRUE/FALSE

The (+) enantiomer of tramadol is more potent inhibitor of serotonin reuptake than the   (-) enantiomer TRUE/FALSE

D isomers of naturally occurring catecholamimes are 10x more potent than the L isomers TRUE/FALSE

Thiopentone is a drug which has stereoisomers TRUE/FALSE


BT_PM 1.22

Tapentadol (Palexia) is relatively new, but has some major advantages over conventional mu agonists. Several surgeons I work with now use it for their routine postop pain control rather than oxycodone.

T/F Tapentadol is a combined µ agonist and SSRI

T/F Tapentadol causes less constipation compared to oxycodone

T/F Tapentadol has a similar rate of abuse and diversion as oxycodone

T/F Tapentadol is ineffective in neuropathic pain

T/F Tapentadol is safe to use in a breast feeding mother