Pharmacokinetics

Question 1

What is the journey of a drug?

Answer 1

Administered, absorbed
Distributed
Metabolised
Excreted
Voided/Removed

Question 2

List some administration routes for drugs

Answer 2

Dermal
Intramuscular
Subcutaneous
Intraperitoneal
Intravenous
Inhalation
Ingestion

Question 3

What are the two pathways that drugs move throughout the body via

Answer 3

Bulk flow transfer and diffusion transfer

Question 4

What is bulk flow transfer

Answer 4

drugs that move via the blood

Question 5

What is diffusion transfer

Answer 5

When drugs move molecule by molecule over short distances

Question 6

What pH are most drugs

Answer 6

Most drugs are either weak acids or weak bases

Question 7

What are factors that affect drug distrubution

Answer 7

Extracellular binding (plasma protein binding)
Regional blood flow
Capillary permeability
Localisation in tissues

Question 8

What are the two major routes of excretion?

Answer 8

Kidney and liver

Question 9

What happens to drugs in the kidneys

Answer 9

1. Glomerulus - Bioactive drug filtered but drug protein complexes aren’t bc too big
2. Proximal tubule is where active secretion of acids and bases happens - some lipid soluble drugs reabsorbed
3. Proximal and distal tubules - lipid soluble drugs reabsorbed

Question 10

Why might intravenous sodium bicarbonate increase aspirin excretion

Answer 10

Sodium bicarb increases urine pH so ionises aspirin. This means it’s less lipid soluble and less reabsorbed from the tubule, increasing it’s rate of excretion
- pH partition hypothesis

Question 11

What are other routes of excretion other than the kidney and liver?

Answer 11

Skin
Lungs
GI secretions
Saliva
Sweat
Milk
Genital secretions

Question 12

What is biliary secretion?

Answer 12

Concentrate large molecular weight molecules

Question 13

What does the liver do to excrete drugs

Answer 13

Biliary secretion and active transport systems into bile

Question 14

What leads to drug persistance?

Answer 14

Enterohepatic cycling

Question 15

What is first order kinetics (most drugs)

Answer 15

Amount of drugs decreases at a rare that is proportional to the conc of drugs remaining in the body

Question 16

What is zero order kinetics?

Answer 16

Amount of drug decreases at a rate independent of the conc of drug remaining in the body.

Question 17

What does zero order kinetics imply about the metabolic process

Answer 17

A saturable, usually enzymatic, metabolic process

Question 18

What is bioavailability

Answer 18

Proportion of the administered drug that is available within the body to exert its pharmacological effect

Question 19

What is the apparent volume distribution?

Answer 19

The volume in which a drug appears to be distributed - indicator of the pattern of distribution

Question 20

What is the biological half life?

Answer 20

Time taken for the conc of drug (in blood/plasma) to fall to half its original value

Question 21

What is blood plasma clearance

Answer 21

The vol of blood plasma cleared of a drug in a unit of time (if made up of multiple steps, is the sum of these steps)

Question 22

What methods are used to cross lipid barriers in the body?

Answer 22

Diffusing through the lipid
Diffusing through aq pores in the lipid (polar only
Carrier molecules
Pinocytosis

Question 23

What is the pH partition hypothesis?

Answer 23

in order to undergo passive diffusion, the drug best diffuses in it’s unionised form
- when the pH of the environment is below the pKa of the drug in question, the majority of the drug is unionised and thus readily diffuses

Question 24

What is ion trapping?

Answer 24

If the pH of the environoment is too far above the drug’s pKa then the drug can become ‘ion trapped’ as it is mainly in ionised form and therefore isn’t passively diffused much

Question 25

Why is the fact most drugs are either weak acids or weak bases significant to think about?

Answer 25

Because non polar substances can freely dissolve in non polar substances eg lipid membranes, but since they aren’t neutral, they exist in both ionised and non ionised forms in a dynamic equilibrium

Question 26

What does the ratio of the ionised to un-ionised drugs depend on?

Answer 26

pH of the environment and pKa of the molecules

Question 27

What is enterohepatic cycling?

Answer 27

Drugs/metabolites are excreted into the gut, reabsorbed and taken back to the liver to be excreted again