The original college viva text reads:
This viva will test knowledge of pharmacokinetics and statistics. Draw the concentration time curve for an intravenous bolus of fentanyl. At this Viva candidates were asked to draw a concentration – time curve for an intravenous bolus of fentanyl, to label it and describe the information relating to that curve. Candidates were also asked about volume of distribution, half-life and clearance. In the second part to this Viva candidates were shown and asked to
describe various types of data, mean and median values, normal distribution and critical evaluation of a study.
To make this gibberish useable, it has been rewritten using the venerable Brandis physiology viva textbook as a template of style and depth.
A pharmacokinetic compartment is a mathematical concept which describes a space in the body which a drug appears to occupy. It does not need to correspond to any specific anatomical space or physiological volume.
A single compartment model of pharmacokinetics describes a drug being distributed in a single volume inside the body, from which it is then cleared.
This can be represented as a diagram:
Drugs which are highly water soluble and which are confined to body water as a single compartment, for example aminoglycosides.
A multi-compartment model accounts for the differences in the rate and volume of drug distribution to different tissues and body fluids. Each compartment represents a space which has distinct pharmacokinetic distribution characteristics.
Distribution of drugs from the blood into the tissues is an important factor in pharmacokinetics of anaesthetic drugs
The three phases of distribution are
These phases can be expressed as a polyexponential curve of drug concentration over time:
The polyexponential curve has multiple exponents which can be interpreted as half-lives of each distribution phase.