9) Pharmacokinetics

Question 1

Define pharmacokinetics.

Answer 1

What the body does to a drug

Question 2

Define pharmacodyanmics.

Answer 2

What a drug does to the body

Question 3

What do we mean when we describe a route of administration as being parentral?

Answer 3

When it’s administered it isn’t absorbed through the GI tract and therefore doesn’t undergo first pass metabolism. (subcutaneous/intramuscular/intravenous injection, inhalation, transdermal)

Question 4

What is the therapeutic ratio? How is it calculated?

Answer 4

The range of concentrations over which the drug is both effective and non-toxic.

Calculated by the maximum tolerated dose/minimum effective dose (in practice this means the LD50/EC50)

Question 5

How may the oral bioavailability be calculated from a graph?

Answer 5

(Area under the curve oral / Area under the curve IV) x 100

Question 6

Describe the First Pass Effect

Answer 6

Substances taken into the body enterally (via the GI tract) are taken straight to the liver via the hepatic portal vein. They then move through the liver and metabolisation reducing the level of the drug that is gonna leave via the regular hepatic vein and therefore less is pumped round the body.

Question 7

Approximately how much paracetamol is metabolised by the first pass effect?

Answer 7

90%

Question 8

Explain the concept of the use of a precipitant drug.

Answer 8

Object drugs (class I) are used at a much lower concentration than there is plasma protein binding sites. Whereas, precipitant drugs (class II) are used at a much higher concentration of drug than there is plasma protein binding sites.

When the drugs are administered simultaneously, Class I drugs are displaced by Class II, raising the free levels of the object drug (class I drug) and therefore you get more in the plasma.