Pharmacokinetics

Question 1

What is the definition of pharmacokinetics?

Answer 1

The study of movement of drug molecules in the patient/animal
- Describes ADME processes

Question 2

What is the definition of pharmacodynamics?

Answer 2

The study of action of drug, including time-course of actions

Question 3

How is the dosage of drug determined?

Answer 3

• The desired effect has been shown to occur after administration of the dose - due to the pharmacodynamic properties of the drug
• If the drug is presented at the target site at a connection that is therapeutically effective, this is dependent on the pharmacokinetic properties of the drug

Question 4

What is ADME?

Answer 4

Administration
Distribution
Metabolism
Excretion

Question 5

Why is water solubility essential?

Answer 5

• For the site of administration to achieve absorption
• For a drug to be distributed
• At the site of action to reach the biochemical target (receptor, enzyme, etc)
• For excretion

Question 6

What is plasma’s role in drug solubility?

Answer 6

Plasma carried the drugs to site of action (except for locally acting drugs)

Question 7

Routes of administration?

Answer 7

• Intravenous injection (i.v.)
• Intramuscular injection (i.m.)
• Subcutaneous injection (s.c.)
• Epidural injection
• Intra-articular injection
• Intra-peritoneal injection
• Oral

Question 8

Types of oral administration?

Answer 8

• Tablets
• Capsules
• Powders
• Solutions
• Suspensions

Question 9

IV route…

Answer 9

• Fastest route to blood
• 100% bioavailability

Question 10

Intramuscular route…

Answer 10

• Slower than IV route
• Suitable for slow release drugs

Question 11

Subcutaneous route…

Answer 11

• Slower than IV
• Suitable for slow release drugs

Question 12

Oral delivery or drugs…

Answer 12

• Tablets and capsules swallowed
• Solutions and suspension by oral syringe
• Solutions and suspensions by nasogastric tube or orogastric tube

Question 13

Oral tablets include excipients including…

Answer 13

• Binders
• Glidants/lubricants
• Disintegrants
• Preservatives
• Colours
• Coatings

Question 14

Absorption factors include…

Answer 14

• Age
• Species
• Gender
• Genetic factors
• Metabolism
• State of health/disease

Question 15

Benefits of oral disintegration…

Answer 15

• Larger surface area to volume ratio after disintegration
• Faster dissolution

Question 16

Lipinskis guidelines developed in 1997

Answer 16

Rule of 5
- No more than 5 H-bond donors
- No more than 10 H-bond receptors
- Molecular weight less than 500
- logP < 5 (P is octanol/water partition coefficient)

Question 17

AUC (area under the curve) results

Answer 17

The area under the curve shows how much the target tissue has been exposed to the drug

Question 18

What is volume of distribution?

Answer 18

Volume of distribution is the theoretical volume that would be necessary to contain the total amount of administered drug at the same concentration as is observed in the blood plasma
- Vd = total amount of drug in the body/concentration of drug in blood plasma

Question 19

How does the drug leave the blood?

Answer 19

Small-molecule drugs can pass through the endothelial cells or diffuse through them to get into the interstitial fluid space in the tissue

Question 20

What is tissue perfusion?

Answer 20

• Affects how rapidly drugs are distributed to different tissues
• Varies between animal species
• Distribution of drugs is rapid to well vascularised tissues
• Distribution of drugs is slow to poorly vascularised tissues

Question 21

Example of tissue perfusion…

Answer 21

Pentothal
- Anaesthetic in veterinary
- Acts in brain within a few minutes
- Redistributed slowly to fat from the brain
- Obese animals recover quickly from anaesthesia
- Lean breeds of dogs have prolonged recoveries

Question 22

What is protein binding in plasma?

Answer 22

Drugs bind to proteins e.g. albumin
- Slow dynamic equilibrium between drug free and complexed drugs
- Drugs can only pass through the capillary wall and move into target tissue if not bound to protein
- Drugs complexed to albumin cannot pass through