Introduction to Biopharmaceutics Flashcards
Biopharmaceutics is..
The study of how physiochemical properties of drugs, dosage forms and routes of administration affect the rate and extent of drug absorption.
Why is Biopharmaceutics important?
There is a knock on effect on the drug, and in turn - the patient.
What does the body to the drug? (4)
ADME
Absorption
uptake into system
Distribution
transfer to body fluids and tissue
Metabolism
transform into metabolites
Excretion
removed
How can we know the amount of drug in the body?
Plasma concentration
The higher the plasma concentration, the higher drug concentration.
What is the Therapeutic window?
The minimum effective concentration.
C max (plasma conc max), what would this be in IV administration?
Same as plasma drug concentration at 0 because no absorption phase.d
What is the Toxic range?
The minimum toxic concentration.
Why are repeated doses needed?
Because plasma concentration decreases over time and fall before therapeutic range.
What is the onset of time?
The time where the plasma concentration first exceeds the therapeutic window.
What is AUC?
the exposure of the body to the drug.
Equation for AUC
IV administration
Co (initial conc) / elimination rate constant
What is the plasma half life?
Time taken for the plasma concentration of a drug to fall by 50%
Equation for plasma half life:
t1/2 = t2 - t1
Is the plasma half life constant?
Yes because it follows first order kinetics.
Long plasma half life means…
more time can pass before taking a second dose.
What is the volume of distribution?
an indication of how likely a drug is to remain in the body or go into tissues.
Equation for volume of distribution:
Vd = D / Co
D = IV dose (mg) Co = initial plasma conc mg per L
Clearance is…
the volume of plasma from which the drug is eliminated per unit time L per H.
hepatic and renal clearance.
Equation for AUC in oral administration:
D x F / CL
D = dose F = bioavaliability CL = clearence
Bioavaliability, F, is..
the fraction of the dose that reached systemic circulation.
What is F in IV administration?
1 or 100%
What is F in oral administration?
F < 1 due to pre-systemic effects
How can food affect drugs?
Affects drug stability, dissolution and absorption due to food components which may stimulate enzyme activity (this causes breakdown of drug before it reaches target)
