Pharmacology

Question 1

What does the plasma concentration of a drug allow you to do?

Answer 1

Create a dosing regimen for each specific patient as it dictates the ability of a drug to reach its target organ in an effective concentration

Question 2

First Order Kinetics

Answer 2

The rate of elimination is directly proportional to the concentration of drug
Half life is constant

Question 3

Kel

Answer 3

Kel represents the fraction of drug eliminated per unit of time

Question 4

Zero Order

Answer 4

Rate of elimination is independent of drug concentration
Half life is not constant
Drug could build up in body leading to toxic side effects

Question 5

Volume of Distribution

Answer 5

Proportionality factor that relates the amount of drug in the body to the concentration of drug measured in the plasma

Question 6

What is Vd affected by?

Answer 6

Drug permeability across tissue barriers
Binding within compartments
pH partition

Question 7

Why is Vd important?

Answer 7

Used to calculate drug dose
High Vd - accumulated in peripheral tissues
Low Vd - confined to the plasma
Drug with a higher Vd tends to require a higher initial dose

Question 8

How can we calculate Vd and C0 from a graph?

Answer 8

By measuring and then plotting plasma concentrations of drug over time

Question 9

How is half life useful?

Answer 9

It allows the clinician to estimate the frequency of dosing

Question 10

Plasma Clearance

Answer 10

The volume of plasma cleared of drug per unit time

Question 11

Steady State

Answer 11

The equilibrium point where the amount of drug administered exactly replaces the amount of drug excreted

Question 12

What does optimal therapeutic dosing regimens seek to maintain?

Answer 12

The steady state plasma drug concentration within the therapeutic window for that drug

Question 13

What does the time required to reach steady state depend on?

Answer 13

Half life
The shorter the half life, the quicker steady state is reached (usually given IV)

Question 14

What must be given if the therapeutic concentration must be achieved rapidly?

Answer 14

A large loading dose

Question 15

Vd Equation

Answer 15

Dose / C0

Question 16

Clearance Equation

Answer 16

(0.693 / t1/2) x Vd

Question 17

Loading Dose Equation

Answer 17

Vd x desired plasma concentration

Question 18

Why can the duration of drug action for a given dose vary between individuals?

Answer 18

Certain drug metabolising enzymes display polymorphic expression of activity –> increased or decreased enzyme activity / levels of metabolism

Question 19

Fast metabolisers

Answer 19

Possess wild type enzyme
Lower plasma concentration
Higher concentration of the metabolite
Generally a normal therapeutic effect

Question 20

Slow metabolisers

Answer 20

Possess either a defective enzyme or don’t express enzyme at all
Higher plasma concentration
Lower concentration of the metabolite
Exaggerated therapeutic effect at normal doses –> reduced drug dose

Question 21

Polymorphic Drug Metabolising Enzymes for Alcohol

Answer 21

Alcohol - alcohol dehydrogenase
Acetaldehyde - aldehyde dehydrogenase
Acetate
Water and carbon dioxide

Treat alcoholics by inhibiting aldehyde dehydrogenase –> flushed skin, vomiting, blurred vision, SOB, throbbing headache, confusion, palpitations

Question 22

Liver disease affecting metabolism

Answer 22

The healthy liver facilitates rapid metabolism of lipid soluble drugs
In chronic liver disease this capacity is reduced for many drugs
First pass metabolism is reduced and so bioavailability is much greater

Question 23

Cardiac disease affecting metabolism

Answer 23

Rate of metabolism is dependent on drug delivery to the liver via the bloodstream
Reduced blood flow in cardiac failure
Dose of a drug may need to be decreased for cardiac failure

Question 24

Disease and Altered Excretion (Renal)

Answer 24

Rate of renal elimination is the main factor that determines the duration of action of these drugs
Alteration of renal function will alter renal elimination rate
These drugs have to be used with special care in individuals whose renal function may be impaired

Question 25

What does reduced glomerular flow rate result in?

Answer 25

Less drug filtered
Longer lasting drug action in body
Lower drug dose, increase dose interval

Question 26

What does pharmacodynamics depend on?

Answer 26

Concentration of drug at the receptor
Response at the receptor
Postsynaptic response within cells

All affected by ageing

Question 27

Tolerance

Answer 27

Reduction in response to a drug after repeated administration
Can be pharmacokinetic or pharmacodynamic

Question 28

Pharmacokinetic Tolerance

Answer 28

Altered drug metabolism

Question 29

Pharmacodynamic Tolerance

Answer 29

Receptor internalisation
Receptor down regulation
Decreased activity of intracellular signalling pathways and ion channels

This is desensitisation

Question 30

Factors affecting drug metabolism and excretion

Answer 30

Age
Disease
Genetics
Other drugs taken
Diet
Environmental pollutants