Chapter 8 - Bioavailability Part 1 Flashcards
define bioavailability
availability of the administered dose in the systemic circulation
most drugs exhibit their therapeutic effect through…..
why?
systemic circulation - because this is how the receptor sites are accessible
4 factors that all must exist in order for an oral drug to be 100% bioavailable
-completely released from the dosage form and into GI fluid
-completely stable in GI solution
-pass through epithelium of GI tract
-no 1st pass in gut or liver before reaching systemic circulation
bioavailablity is the ___ and ____ to which an administered dose reaches systemic circulation
rate and extent
(how fast and what amount)
true or false
IV is always 100% bioavailable
true
bioavailablity is a concern with extravascular drugs because the drug only reaches systemic circulation after what?
AFTER IT’S ABSORBED
the 2 parameters of bioavailability
rate of absorption
extent of absorption
3 indicators of the rate and extent of absorption
(the 2 parameters of bioavailability)
Cmax
Tmax
AUC
what is the IDEAL method of measuring bioavailability?
does it always work?
what is done instead?
ideal - clinical effectiveness. ie - lowering blood pressure, lowering blood glucose
however, doesnt always work for things especially something like pain perception
therefore, we can use blood/plasma or urine to measure bioavailability
as mentioned, 2 ways of finding bioavailability are either through blood/plasma or through urine
when is the only time that urine can be used?
ONLY if 10% or more of the drug is excreted into the urine unchanged
true or false
when using urine samples to determine bioavailability, we are measuring the urinary excretion of metabolized drug
FALSE - unchanged drug
explain how a urine sample can be used to determine bioavailability
the rate of drug excretion in the urine depends on the concentration of blood in the plasma
therefore, the rate of urine excretion represents the rate of drug absorption, and the cumulative amount of drug excreted in the urine represents AUC
true or false
a drug that degrades according to first order kinetics is given both as PO and by IV
the half life changes for each of these dosage forms
FALSE - REMAINS THE SAME
true or false
the concentration of drug in the plasma has a direct relationship to the rate of absorption of the drug
TRUE (1st order
“absolute” bioavailability
IV
formula for determining relative bioavailability
F = AUC test/ AUC reference
3 different examples of what the “test” product may be when determining relative bioavailability
generic product
new dosage form
same product made by 2 different manufacturers
true or false
relative bioavailability is expressed as a decimal
FALSE - as a percent
true or false
when determining relative bioavailability, both products may be administered at different doses
FALSE - always given at the SAME DOSE
there is a new product that is intended for extravascular administration
what is the reference?
the IV dose of the product (absolute bioavailability)
the same drug as a different manufacturer is being tested for relative bioavailability
what is the reference?
the innovator’s product
the same drug in a different dosage form is being tested for relative bioavailability
what is the reference
the existing dosage form of the product
symbol for absolute/relative bioavailability
F
formula for absolute bioavailability
F = AUC test/D test
divided by
AUC IV/ D IV
5 methods of determining AUC. which is most popular?
-planimeter
-counting squares
-trapezoidal rule (MOST POPULAR)
-cutting and weighing
-from clearance
2 reasons planimeter is rarely used to determine AUC
instrument has to be calibrated, and procedure is tedious
the AUC can only be calculated from the clearance in what scenario
IV administration
2 things that the cutting and weighing method can determine
AUC 0->t
or to compare the AUC of 2 products
in the trapezoidal method of finding AUC, what is important to note about the first segment?
if the drug is given orally, the first segment is always a triangle!!!!
formula to find area of a triangle (1st segment will be a triangle if drug is given orally)
Area = 0.5 * base * height
formula to find area of a trapezoid
0.5 * base *height (a +b)
explain the trapezoidal method for AUC
find area of triangle (if EV) and the area of all the trapezoids
add them together to get the AUC 0->t
true or false
the half life for a first order reaction is always constant
true
can we measure Co through the bodily fluids
NO - only from calculations/graphs
true or false
you need to find Co for the trapezoidal rule
true
