Session 1 - Pharmacokinetics

Question 1

Describe some patient-related problems that cause prescription errors:

Answer 1

• More rapid throughput of patients
• New drug developments
• Increasing complexity of medical care
• Increased specialisation
• Sicker and older patients
• More elderly patients with co-morbidities

Question 2

Describe some pharmaceutical problems that cause prescription errors:

Answer 2

• There are a vast number of new drugs
• Clinical evidence is produced in patients who are young, relatively healthier and only on one drug at a time.
• Some side effects only unveiled in post-market research
• Blind adherence to guidelines leads to prescription errors where interactions or contraindications exist.

Question 3

Describe some doctor-related problems that cause prescription errors:

Answer 3

• What knowledge is available - is their training in medical school/postgrad level?
• Sleep deprived
• Limited support

Question 4

Describe some Medical problems that cause prescription errors:

Answer 4

• Reduced hours and shift work leads to less exposure to teaching.
• Less ward teaching and feedback
• Poorer morale
• Lack of continuity of care
• Lack of pharmacology training
• too many students

Question 5

Describe some problems that cause prescription errors when prescribing on call:

Answer 5

• Rarely know the patient
• Routine boring jobs - rewrite drug chart/prescribe fluids/prescribe new unfamiliar drugs/prescribe old drugs in absence of result.

Question 6

What key facts should be confirmed before writing a prescription?

Answer 6

Name of drug - approved drug name - no abbreviations
Dose
Strength
Units in full
Frequency
Duration of Treatment
Allergies/adverse effects
Indication
Adherence

Question 7

What are black triangle drugs?

Answer 7

One being intensively monitored, this may be because it is newly released, changed indication, change formulation or a combination product.

Question 8

What drug reactions should be reported?

Answer 8

Black triangle drugs - all suspected reactions
Unlicensed herbal preparations - all suspected reactions
Established products and vaccines - report all suspected serious reactions even if already know and recognised.
All Paediatric reactions

Question 9

Define Pharmacokinetics:

Answer 9

Study of the movement of the drug into and out of the body - what the body does to the drug

Question 10

Define Pharmacodynamics:

Answer 10

Study of the drug effect and mechanism of action - what the drug does to the body.

Question 11

Define Pharmacogenetics

Answer 11

The effect of genetic variability on the pharmacokinetics or dynamics of a dug on an individual

Question 12

Define First order reactions:

Answer 12

A constant fraction of the drug is eliminated at a time - this gives a more predictable reaction - can calculate half life - if plotted on a logarithmic scale it will give a straight line.

Question 13

Define Zero order reactions:

Answer 13

Rate of elimination is constant no matter the concentration of the drug. When active sites of enzymes become saturated at high doses drug which originally followed first order kinetics will switch to zero order.

Question 14

Which types of drugs are more likely to result in toxicity and why?

Answer 14

Zero Order kinetics - small increases in doses may result in the dose saturating metabolising enzymes/binding proteins so will result in a proportionally larger concentration of drug unbound free to react.

Question 15

What is first pass metabolism?

Answer 15

Any metabolism that occurs before the drug has entered the metabolism. This can occur in the gut lumen, gut wall and the liver.

Question 16

What is bioavailability?

Answer 16

The fraction of the dose which finds its way into a body compartment - usually the circulation. (IV bolus = 100%)

Question 17

What factors affect bioavailability?

Answer 17

Drug formulation
Age
Food 
Lipid soluble? - more easily absorbed
Vomiting 
Malabsorption

Question 18

Describe clearance:

Answer 18

The ability of the drug to excrete a drug - normally equates to GFR - half like is inversely proportional to clearance - e.g. if there is a reduction in clearance then half life is increased.

Question 19

What is distribution?

Answer 19

The ability of the drug to dissolve in the body - key factors include protein binding - e.g to albumin and globulins and volume of distribution. Half life is proportional to the volume of distribution.

Question 20

How can the volume of distribution be larger than the volume of the body?

Answer 20

Because drugs are capable of binding to proteins and cell surface receptors which increase the apparent volume of the body even though they are not fluids.

Question 21

What is metabolism (drugs)?

Answer 21

The extent to which the liver breaks down drugs and converts them by conjugating them with other molecules to make them water soluble to that they can be eliminated by the kidney . Metabolism can also convert inactive drugs to ones which are pharmacologically active. Similarly the by products of metabolism may also be pharmacologically active.

Question 22

What is elimination?

Answer 22

Mainly via the kidney although can be via the lungs, breast milk, sweat, tears, genital secretions, bile and saliva.

Question 23

What three processes determine renal excretion of drugs?

Answer 23

Glomerular filtration
Tubular reabsorption
Tubular active secretion

Question 24

What value is represented by the area under the curve?

Answer 24

Total drug exposure

Question 25

Define volume of distribution:

Answer 25

How widely a drug is distributed in body tissues. It can be calculated by dividing the dose by the concentration of the drug at time 0.

Question 26

What is the steady state?

Answer 26

The concentration at which the drug concentration varies less widely - usually at 5 half lives of the drug

Question 27

Define half life:

Answer 27

The time it takes for the concentration of a drug to half.

Question 28

Define Cmax

Answer 28

The maximum concentration in the plasma

Question 29

Define Therapeutic Index:

Answer 29

The window in which the concentration of the drug has a desirable effect clinically. Outside this window the drug is either non-effective or toxic.

Question 30

What patient factors can effect drug pharmacokinetics?

Answer 30

Age
Sex
Fever
Liver/Rena; Function
Exercise
Pregnancy
Immunisation
CVS function
GI Function
Albumin concentration
Alcohol intake