Pharmacokinetics

Question 1

What is Pharmacokinetics

Answer 1

What the body does to the drug

Question 2

Concepts of Pharmacokinetics a drug has to be

Name 5

Answer 2

Available in a suitable form;
Administered by an appropriate route;
Absorbed and distributed – effect; 
Metabolised; and then
Excreted

Question 3

Name 4 stages of a drug in the body

Answer 3

Absorption
Distribution
Metabolism
Excretion

Question 4

Name the two factors of absorption

Answer 4

Physiological

Physico-chemical

Question 5

Describe the Physiological factors of absorption

Answer 5

Time of arrival and contact time at the absorption site.
Total surface area for absorption
Blood flow to the absorbing site

Question 6

Describe the Physio-chemical factors of absorption

Answer 6

Solubility- how soluble the drug is in body fluids
Chemical stability- will it break down readily
Lipid to water partition coefficient- is it more fat-soluble than water-soluble
Degree of ionisation- chemical charge

Question 7

Name the factors affecting the distribution

Answer 7

blood flow,
tissue mass
partition coefficient between blood and tissues

Question 8

Describe protein binding

Answer 8

Plasma proteins such as albumin can bind drug molecules. Drugs bound to plasma proteins are pharmacologically inert, only free drugs are active.

Question 9

Name a drug that can be displaced from plasma binding by another drug

Answer 9

Warfarin can be displaced by aspirin

Question 10

What must a drug be to cross the blood-brain barrier

Answer 10

Highly lipid-soluble (lipophilic)

Question 11

How many phases of metabolism are there?

Answer 11

There are 2

First pass (Oxidation)

Second pass (Conjugation)

Question 12

Describe First Pass Metabolism

Answer 12

The drug is absorbed from the GI tract and passes via the portal vein into the liver where some drugs are metabolised. Sometimes the result of first pass metabolism means that only a proportion of the drug reaches the circulation.

First pass metabolism can occur in the gut and the liver. For example, first pass metabolism occurs in the gut for benzylpenicillin and insulin and in the liver for propranolol, lignocane, chloromethiasole and GTN.

Question 13

Describe Second phase Metabolism

Answer 13

The reactive metabolite is conjugated with another substance which is more water-soluble to allow it to be excreted

Question 14

Describe renal excretion

Answer 14

Glomerular filtration;
Active secretion of ionised drugs into the proximal tubule;
In the distal tubule there is passive absorption and excretion of unionised drugs according to a concentration gradient

Question 15

What is time to onset?

Answer 15

The time it takes for a drug to reach its site of action at a concentration necessary for it to work

Question 16

What is duration of effect?

Answer 16

The time interval where the concentration of drug at its site of action is above its therapeutic concentration – may be prolonged in the elderly or people with poor liver or kidney function

Question 17

What is First Pass metabolism?

Answer 17

when a drug is completely destroyed in the stomach before being absorbed, or when it is metabolised by the liver before reaching the systemic circulation

Question 18

What is half-life?

Answer 18

the time it takes for the peak concentration of a drug in the plasma to reduce by half

Question 19

What is steady-state?

Answer 19

when drug going into the body = drug going out, achieved after 5 half-lives

Question 20

What is clearance?

Answer 20

a measurement of a person’s ability to metabolise and excrete a drug, or how quickly a drug is ‘cleared’ from the blood, affected by renal function, blood pressure and urine pH

Question 21

What is bioavailabily?

Answer 21

the fraction or %age of an administered drug that reaches the systemic circulation after absorption unless given IV where it is 100% of the administered dose

Question 22

Define polypharmacy

Answer 22

A patient on FOUR or more medications

Question 23

What is volume of distribution?

Answer 23

that volume of plasma in which the total amount of drug in the body would need to be dissolved in order to reflect the drug concentration in the plasma

Question 24

Describe pharmacokinetic drug interactions

Answer 24

occurs when one drug alters the absorption, protein binding, metabolism or excretion of another leading to altered bioavailability of the drug to have its pharmacological effect.

Question 25

A pharmacodynamic interaction

Answer 25

occurs with drugs which have similar or antagonistic effects
Morphine acts at opioid receptors as does naloxone, one is an agonist the other an antagonist
Risk of bleeding ↑ if aspirin is added to warfarin

Question 26

Metabolism interaction

Answer 26

Some drugs either induce or inhibit the enzyme required to metabolise another drug