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1

Def: pharmacokinetics

Study of factors which determine the amount of drugs at their sites of biological effect at various times.

Includes

ADME

Absorption

Distribution

Metabolism

Excretion

2

Def: Pharmacodynamics

What the drug does to the body

3

Def: clearance

Volume of plasma cleared of a drug per unit time

4

Def: half-life

Time taken for drug concentration to decline to half its original valu

Depends on volume of distribution and clearance

5

Def: volume of distribution

Volume into which a drug appears to distribute

Theoretical volume that would be necessary to contain the total amount of a drug administered at the same concentration that it is observed in the blood plasma.

High for lipid-soluble drugs

Low for water-soluble drugs

6

What factors can increase the volume of distribution?

Higher Vd indicates a greater amount of tissue distribution.

High lipid solubility (non-polar drugs), low rates of ionisation or low plasma binding capabilities have higher volumes of ditribution than drugs which are more polar, more highly ionised or exhibit high plasma binding.

Vd may be increased by renal failure (due to fluid retention) and liver failure (due to altered body fluid)

7

Vd=

Total amount of drug in body/drug blood plasma concentration

8

What is first order kinetics?

Clearance of durg is always proportional to plasma concentration

Most drugs are in this category

9

What is zero order kinetics?

Clearance of drug is not always proportional to plasma concentration

Saturation of metabolism-> constant rate of elimination regardless of plasma levels

10

Give some examples of drugs with zero order kinetics

Phenytoin

Salicylates

Ethanol

11

What is bioavailability?

Percentage of the dose of a drug which reaches the systemic circulation

100% for IV administration

12

How long is ~ required for a drug to reach a steady state?

Around 5 half lifes

13

What does a loading dose do?

Reduces the time needed to reach a steady state, useful if long or short half life

14

What are some drugs that use loading doses?

Phenytoin

Digoxin

Amiodarone

Theophylline

15

What are the indications for therapeutic drug monitoring?

Ix lack of drug efficacy (possibility of poor compliance)

Suspected toxicity

Prevention of toxicity

16

What are three drugs that must have therapeutic drug monitoring?

Aminoglycosides

Vancomycin

Li

17

What are some dugs that have therapeutic monitoring?

Phenytoin

Carbamazepine

Digoxin

Ciclosporin

18

Does Warfarin undergo therapeutic drug monitoring?

Not monitored per se, it is the biological effect that is monitored rather than the plasma drug level

19

What is first pass metabolism?

Metabolism and inactivation of a drug before it reaches the systemic circulation

i.e. pre-systemic elimination

Occurs in gut wall and liver

20

Gives some examples of drugs that undergo FPM

Propranolol

Verapamil

Morphine

Nitrates

21

What are the pathways of drug metabolism and elimination?

Excreted unchanged by the kidney e.g. frusemide

Phase 1 metabolism and then renal excretion

Phase 2 metabolism and then renal excretion

22

What is phase 1 metabolism

Creation of reactive, polar functional groups.

Oxidation: usually by cytochrome P450 system

Reduction and hydrolysis

23

What is phase 2 metabolism?

Production of polar compounds for renal elimination

Either the drug or its phase 1 metabolite

Conjugation reactions: glucuronidation, sulfonation, acetylation, methylation

24

What is the principle method of elimination?

Renal, depends on GFR

25

How many subtypes of CyP450 are there?

>11

26

What is the most important CyP?

What proportion of drugs does it metabolise?

CyP3A4

>30% e.g. CCBs, beta blockers, statins, benzos

27

What is the second most important CyP?

What proportion of drugs does it metabolise?

CyP2D6

>20% e.g. antidepressants, some beta blockers, opiates

28

Prodrugs: -->

L-DOPA

Dopamine

29

Prodrugs: -->

Enalpril

Enalprilat

30

Prodrugs: -->

Ezetimibe

Ez-glucuorinde