DEVELOPMENT OF THE DOSAGE REGIMEN

Question 1

Define absorption:

Answer 1

Orally administration drugs must be dissolved from its excipients before it can be absorbed

Question 2

Define distribution:

Answer 2

Only drugs in a unbound state in the plasma can be distributed to target tissues

Question 3

Define metabolism:

Answer 3

• mainly occurs in liver
• first pass hepatic metabolism for orally administered drugs
• creating water soluble drugs so that they can be excreted by the kidneys

Question 4

Define elimination/excretion:

Answer 4

• mainly occurs in kidneys
• only water soluble metabolites can be excreted via the urine

Question 5

What do the 4 pharmacokinetics directly affect?

Answer 5

Onset: impacted by rate of drug absorption and distribution
Intensity of drug action: impacted by the amount of drug absorbed and distributed
Duration of drug action: impacted by rate of drug metabolism and elimination

Question 6

What is a drug dosing interval?

Answer 6

Rate of drug metabolism and elimination

Question 7

What is bioavailability?

Answer 7

Amount of the administered drug dose that plasma in a chemically unchanged and/or biologically active form

Question 8

What factors influence bioavailability?

Answer 8

• first pass hepatic metabolism
• drug formulation and incomplete absorption
• plasma protein binding

** drugs administered through the oral route rarely demonstrate 100% bioavailability**

Question 9

Process of distribution in drug regimen:

Answer 9

Process by which a drug leaves the blood stream and enters body tissues (this is reversible)
- impacted by blood flow, solubility of the drug, organ size, etc

Apparent volume of distribution

Ratio of the amount of drug in the body to the drug concentration in the plasma

Question 10

What is apparent volume of distribution?

Answer 10

• the volume into which a drug is known to distribute within the body
• the volume is expressed in: litres or litres/kilogram

Question 11

Why is the apparent volume of distribution important?

Answer 11

Vd is used to calculate the dose of drug required to achieve a specified concentration of drug in the plasma

Question 12

What is therapeutic concentration?

Answer 12

For a drug to exert a therapeutic effect, the concentration of the drug (in plasma) must fall within the therapeutic concentration range of that drug

This is most often expressed as:
- mg/L
- ug/mL

Question 13

What are the therapeutic concentration ranges?

Answer 13

Plasma concentration= 2
- normal therapeutic response

Plasma concentration= 5
- TOO HIGH, cause adverse effects

Plasma concentration= 0.5
- TOO LOW, produce little effect

Question 14

What is a loading dose?

Answer 14

Used to quickly achieve a high therapeutic plasma concentration of drug

Wd = [D]o x Vd

This can also be used to calculate a single dose

Question 15

What is the drug equilibrium and the plateau principle?

Answer 15

The T1/2 life of a drug provides useful measure called the plateau principle
- 95% of the steady state will be reached after 4 half-lives

Question 16

How does the plateau principe work?

Answer 16

Drug equilibrium is reached once 4 half lives of the drug has passed
- What goes into the systemic circulation is balanced by what is eliminated

This means that after you start, stop or change a dosage regimen, it will take 4 half lives for the concentration of the drug in plasma to be stable
- the therapeutic effect may not be robust until this timeline has elapsed

Question 17

What is repeated dose drug therapy?

Answer 17

Most drugs are prescribed for any extended period

Important to keep the concentration of an analgesic drug within the therapeutic range to control a patients pain

Question 18

What is a dosing interval?

Answer 18

Amount of time between doses

Question 19

What is clearance?

Answer 19

Volume of plasma completely cleared of a drug per unit of time (L/hr)

Question 20

What is the maintenance dose?

Answer 20

Drug dose required to maintain plasma concentrations within the therapeutic range

This dose should always be smaller then the loading dose