Adsorption, Distribution, Metabolism, Elimination

Question 1

What is the core concept of drug absorption?

Answer 1

The process by which a drug moves from its site of administeration to the systemic circulation

Question 2

What four physiological processes govern the time course of a drug?

Answer 2

• Adsorption
• Distribution
• Metabolism
• Excretion

Question 3

What does absorption involve?

Answer 3

Drugs crossing cell membranes e.g lipid bilayers

Question 4

What are the three ways that drugs can cross cell membranes?

Answer 4

• Passive diffusion through a lipid
• Solute carrier-mediated transport
• Diffusion through aqueous pores

Question 5

What chemical and physical factors affect drug uptake?

Answer 5

• The drugs physiochemical properties
• Dissolution in water is affected by molecular size and degree of hydrophobicity
• Drug diffusion across membranes is influenced by the concentration gradient

Question 6

What biological factors affect drug uptake?

Answer 6

• Vascularity and local blood flow to the absorption site
• Gastric content
• Surface area for absorption
• Local pH
• Local enzymes in the gut wall and liver
• Specific transport systems in the GIT allow absorption of nutrients

Question 7

How might you by-pass drug absorption?

Answer 7

the iv route

Question 8

What is the iv drug route useful for?

Answer 8

• Rapid effects
• Fluid therapy
• Precise dosing
• Administration of short-acting drugs
• Administration of irritant drugs

Question 9

How might you be able to modify absorption through formulation?

Answer 9

• Depot injections (e.g particle size)
• Controlled/ Sustained release products

Question 10

What is drug distribution?

Answer 10

The reversible passage of drugs between tissues, organs and compartments

Question 11

By what mechanism do drugs move around the body?

Answer 11

Bulk flow in the blood

Question 12

What influences drug distribution?

Answer 12

Degree of reversible binding to proteins in plasma, only unbound drugs can distribute into tissues

Question 13

What does distribution between different drug compartments depend on?

Answer 13

• Physiochemical characteristics of the drug
• local pH
• Blood flow
• Transport mechanisms
• Disease Process
• Protein binding within compartments

Question 14

What does individual variation in drug response refer to?

Answer 14

The concept that there are differences in response between individuals in the same drug dosage

Question 15

What is drug metabolism?

Answer 15

The chemical transformation of a drug into one or more products within the body

Question 16

Where does drug metabolism predominantly occur?

Answer 16

In the liver, cytochrome p450 plays an important role

Question 17

What is the phase 1 reaction?

Answer 17

CYP450 enzymes introduce a reactive chemical group, producing a metabolite more reactive than the original drug

Question 18

What is the phase 2 reaction?

Answer 18

Anabolic- involves conjugation, produces inactive, polar products readily excreted in the urine

Question 19

What is the major factor that accounts for differences in drug effects across species?

Answer 19

Biotransformation

Question 20

What is drug interaction?

Answer 20

The process by which a substance alters the action and/or kinetics of a drug

Question 21

What may drug interactions result in?

Answer 21

effects that are either beneficial or deleterious

Question 22

What is drug elimination?

Answer 22

The removal of a drug through the body via metabolic and/or excretory processes

Question 23

What is the main route of drug elimination?

Answer 23

Via the kidneys, thus renal function has a major influence on drug plasma concentrations