Introduction to Biopharmaceutics Flashcards
What is biopharmaceutics?
The study of how the physiochemical properties of drugs, dosage forms + routes of administration affect the rate + extent of drug absorption
What is plasma conc?
Measurements of drug in the body usually limited to blood or plasma
What happens in oral administration?
Drug release + dissolution Absorption into system circulation Elimination = excretion or metabolism OR Distribution = drug in tissues = pharmacological effect
What happens in IV administration?
System circulation
Elimination = excretion or metabolism
OR
Distribution = drug in tissues = pharmacological effect
What assumptions do we make?
Drug conc in plasma increases
= increases drug conc at target site
= increases pharmacological effect
What happens if you inject single dose?
Plasma conc will not stay like that forever
What does graph look like for IV?
At T=0 high conc
Then decreases over time
What happens if plasma conc is in the toxic range?
Experience serious side effects
What is therapeutic window?
Between min toxic range and min effective conc
What happens if drug conc is in the sub-therapeutic range?
Drug will have no effect
Why is a 2nd dose given?
To increase plasma conc to therapeutic window
What is onset time?
Plasma conc first exceeds minimal therapeutic conc
When is the onset time for IV + why?
T=0
= rapid onset of action
What is duration of action?
Time within therapeutic window
What does the area under the curve tell us?
Total exposure to the drug
What is the duration of action dependent on?
Initial conc
How do you calculate rate of elimination?
Kel X D
What is plasma half life?
Time taken for plasma conc of a drug to fall by 50%
Is plasma half life constant?
YES
How does plasma half life proceed?
1st order reaction
What does rate depend on?
Initial drug conc
What is long plasma half life?
Plasma conc will remain in therapeutic window for longer
What happens if you have a shorter half life?
You need more frequent dosing
What can dosing also depend on?
How narrow or wide therapeutic window is
What is vol of distribution?
Theoretical fluid vol needed to contain the drug at same conc found in the plasma
What is vol of distribution affected by?
Plasma proteins
What does it mean if there is a larger vol of distribution?
Distribution of drugs into tissues
What happens to bound drugs?
Confined to plasma
What happens to unbound drugs?
Can be distributed into tissues
What does there mean if there is a high bound drug fraction (fb)?
Lower vol of distribution
What is clearance?
Vol of plasma from which the drug is eliminated per unit time
How is the drug eliminated?
Metabolism = liver Excretion = kidneys
Describe the graph for oral administration
Conc starts at 0
Then increases to a peak = Cmax
Then decreases again
What is Tmax?
The time taken to reach Cmax
How do you calculate exposure?
Area under curve (AUC)
What happens before Cmax is reached in the oral administration graph?
Drug is being absorbed in GI tract
What is bioavailability?
Fraction (%) of dose that reaches systemic circulation
What is the bioavailability fraction for IV?
F = 1 as entire dose is administered into bloodstream
What is the bioavailability for oral?
F < 1 due to pre-systemic effects
How many food affect drug stability, dissolution + absorption?
Change change pH = slow dissolution
Food components, bile salts, gastric retention + enzyme activity
What is bioequivalence?
Equivalent rate + extent of absorption between formulations
What must AUC, Tmax + Cmax all fall within to be considered bioequivalent?
80-125%
