B3 Drugs

Question 1

What is pharmacokinetics?

Answer 1

Pharmacokinetics is the factors which affect drug journey in the body, such as ADME.
ADME: Absorption, Distribution, metabolism and excretion of a drug.

Question 2

What is absorption?

Answer 2

Absorption is the accumulation of drugs in the body compartments

Question 3

What is pharmacodynamics?

Answer 3

Pharmacodynamics is how the drug affects living organisms.

Question 4

What is distribution?

Answer 4

Distribution is the different areas and organs that are influenced by drugs.

Question 5

What are xenobiotics?

Answer 5

A foreign compound in the body not naturally produced.

Question 6

What are the methods of drug administration?

Answer 6

Oral/Rectally
Intravenously: Plasma
Inhalation: Lungs -> Plasma
Intrathecal (spinally): CSF -> Brain -> Plasma
Percutaneously (ointments): Skin -> Gut

Question 7

Which methods of drug administration in the oral/rectally?

Answer 7

Oral/Rectum has 3 methods of drug administration to plasma
1) : Gut-> Plasma
2) : Gut-> Portal System -> Liver -> Plasma
3) Gut -> Portal System -> Liver-> Bile -> Gut -> Plasma

Question 7

How are drugs excreted?

Answer 7

From plasma to:
Kidney -> Urine
Breast milk
Sweat
Placenta -> Fetus

Question 8

How are oral drugs protected from the low pH of the stomach?

Answer 8

They either have an enteric acid coating to withstand the low pH or a bicarbonate coating to increase ph.

Question 9

What are the factors that affect drug absorption?

Answer 9

Blood perfusion
SA to Vol ratio
Ph of lumen
Bile and mucus
Epithelial membrane components.

Question 10

How does drug composition change following membrane uptake?

Answer 10

Broken down into an ionised and unionised form.

The unionised form can easily cross the membrane for absorption in the lumen via passive diffusion.

The ionised form cannot cross the membrane. It exists in the form of a weak acid or base. The proportion of each is affected by the acid disassociation constant in the organ.

A low pKa will decrease the weak acid and increase weak base.
A high pKA will increase weak acid and decrease weak base.

Question 11

What is Cmin?

Answer 11

Lowest concentration of a drug.

Question 12

What is Kabs?

Answer 12

Rate constant of abosorption which is a measure of drug transfer to body compartments like organs.

Question 13

What is Cmax?

Answer 13

Maximum concentration of a drug/

Question 14

How does Kabs influence drug action?

Answer 14

Low Kabs means lower Cmax but there is a longer duration of drug action. High Kabs means there is a greater duration of drug action.

Question 15

What is Cp?

Answer 15

Plasma concentration of a drug?

Question 16

How is Cp influenced by absorption?

Answer 16

Cp increases during absorption; once absorption is complete, Cp decreases.

Question 17

How is the ionised form of the drug transported?

Answer 17

Ionised drugs are transported across membranes by carriers:
->Passive facilitated diffusion
-> Paracellular uptake via the cleft between two epithelial cells
->Facilitated passive diffusion
-> Pinocytosis- cell drinking of fluid via vesicle budding

Question 18

What is the therapeutic dose regimen?

Answer 18

Process which determines the optimal dose of medication to administer to a patient. This is due to the high variance in patient response to drug vs the actual Cp variance.

Question 19

What is the process of therapeutic dose regimen?

Answer 19

Estimate initial dose
Adjust for target dose
Increase dosage in loading dose
Lower dosage in maintenance dose where Cp is equal to elimination

Question 20

How does diet affect drug absorption?

Answer 20

Grapefruit juice reduces drug elimination which can lead to toxicity.
High fibre foods adsorb to bile, which means it forms a thin film. This prevents bile from eliminating lipophilic drugs and leads to toxicity,
Drugs administered to affect intestinal transit time will affect the absorption of other drugs.

Question 21

How does adrenaline affect local anaesthetic action in the body?

Answer 21

Adrenaline is administered following local anaesthesia to decrease absorption and increase elimination

Question 22

What is the volume of the body compartments?

Answer 22

Total volume is 42L
IC vol: 28L
EC vol: 14

Question 23

What is the composition of EC vol?

Answer 23

EC vol 14
Intravascular volume (plasma) 3L and Extravascular volume 11 L
–> Interstitial 10.5L
–>transcellular 0.5L

Question 24

What is the difference in distribution between bound and free drugs?

Answer 24

Bound drugs to plasma proteins cannot easily cross the body compartments. Free drugs can move easily within compartments and across compartments.

Question 25

What is volume distribution?

Answer 25

Volume distribution is the theoretical volume of a drug uniformly distributed in the body to reach the same Cp.

Question 26

How does volume distribution affect volume of drug administer?

Answer 26

A low volume distribution occurs when drugs are limited to the plasma compartment such as heparin, so it is more potent, and less volume is required.
A high-volume distribution is when the drug is not limited to the plasma compartment, such as morphine. Therefore, a higher volume of the drug is required.

Question 27

What are helicobacter pylori?

Answer 27

Heliobacteria pylori are bacteria which infect the stomach. It is present in 50% of the population and won’t cause any side effects in majority of people. It may release urease an enzyme which breaks down urea into NH3 and H2CO3. This disrupts the stomach lining and leads to ulcer formation.

Question 28

How do inflammatory mediators influence gastric acid secretion?

Answer 28

Prostaglandin act on receptor activation to decreases gastric acid secretion and increases mucosal and enzyme secretion. This is in response to inflammation.

Question 29

How do protein pumps treat stomach ulcers?

Answer 29

Proton pump inhibitors in low pH in the gastric acid are converted into sulphenamides and use ATPase to irreverisbly inhibit the pump.