ILA 3 - pharmacokinetics and pharmacodynamics

Question 1

define pharmacokinetics.

Answer 1

• branch of pharmacology concerned with the movement of drugs within the body. Drugs pass through 4 different phases:
• absorption
• distribution
• metabolism
• excretion

Question 2

define pharmacodynamics.

Answer 2

study of a drugs molecule, biochemical and physiological effects or actions

Question 3

principles of protein binding

Answer 3

• protein binding lowers the free concentration of a drug
• ideally the induction drug should have a low protein binding to enable high initial plasma concentration
• if strongly proetin bound, then the plasma concentration of free drug will be lower
• agents with higher protein binfing capacity are associated with longer duration of action
• agents with lower proetin vinding capacity are associated with shorter duration of action

Question 4

pros and cons of protein binding

Answer 4

protein binding - less free drug - not as much used - slower duration

no protein binding - more free drug in blood - used up quicker - more potent

Question 5

pharmacokinetic model.

Answer 5

• distribution
• rapid equillibrium
• elimination

Question 6

explain in terms of the drug distribution of the IV drug why an additional volatile drug needs to be given as soon as the patient is asleep. what would happen if it was not given?

Answer 6

• IV - high initial plasma conc - drug rapidly enters well perfused areas eg brain
• then enters less well perfused areas - lowering the plasma conc
• conc in highly perfused tissues then decreases
• good as a quick anasthesia, but wears off quickly
• if second anasthesia agent isnt given, the plasma conc will decrease and the patient will start to wakwe up

Question 7

sometimes surgeries require the administration of a muscle relaxant drug, why?

Answer 7

• this is an antagonist of acetylcholine at the postsynaptic nicotinic receptor in the neuromuscular junction

Question 8

give an example of a full / complete agonist.

Answer 8

morphine and nicotine

Question 9

give an example of a partial agonist.

Answer 9

buprenorphine

Question 10

give an example of an inverse agonist.

Answer 10

antihistamine

Question 11

give an example of a competative antagonist.

Answer 11

naloxone

Question 12

give an example of a non-competative antagonist.

Answer 12

ketamine

Question 13

give an example of a irreversible antagonist

Answer 13

phenoxybenzamine

Question 14

name the drug targets eg receptors and give an example.

Answer 14

receptors - nicotinic
enzymes - ACE
transporters / carrier proteins - proton pump
ion channels - canclium channel bockers

Question 15

explain why a lower dose of morphine than normal is needed with renal imparement.

Answer 15

Morphine is metabolised in the liver to morphine 6 glucuronide which is more potent than morphine. It is excreted by the kidneys, therefore if a patient has renal failure it will not be as readily excreted. This requires the dose and frequency of administration to be reduced.
Mild renal impairment → should use 75% of normal dose so between 2.5mg and 5mg. Dose interval should be 6 hourly.
Moderate renal impairment → should use 50% of the normal dose so between 2.5mg and 5mg. Dose interval should be 6-8 hourly.
Severe renal impairment → use small doses. Dose should be between 1.25mg and 2.5mg. Dose interval should be 8-12 hourly.