Flashcards in 11/9 Pharmacology Deck (38)
The fractional extent to which a dose of drug reaches the systemic circulation.
what is the equation for bioavailability (F)?
F= [AUC/Dose]/[AUC IV/ Dose IV] where AUC is are under the curve of concentration vs. Time
the reduction in bioavailability of a drug that results from its metabolism or excretion prior to reaching the systemic circulation
what is the equation for first pass elimination?
F=(1-ER) * f where f is the fractional absorption and ER is the extraction ration
what is the F for IV drugs?
1 of course since it all reaches the circutlation
which of the following most correctly discribes the first pass effect of pharmacology?
elimination of enterally administered drugs by metabolism or excretion before it gets to the circulation.
how does absorption compare to bioavailability
this is a common mistake...they are not the same!!! absorption is the rate that drug initally enters the body system. Bioavailability is the amount of drug that is in the circulatin after first pass effects.
what are the factors that affect the bioavailability of a drug?
depends on the route of administration and is a function of absorption and first pass elimination.
what is the conceptially way of explaining the math of bioavailabilty
the ratio of the conc. of the drug per time per the dose given compared to the what it would be for an IV administered drug.
what are the two organs of first pass elimination?
the liver and the lungs
the 2/3 rule!!! (you missed it on the last test after all!)
Kg * 2/3 =water; water*2/3 is Intracellular; water*1/3 is extracellular. 2/3 of extracellular is interestitial and 1/3 of extracellular is intravascular. then fat is
a measure of the apparent space in the body available to contain the drug
Volume of distribution (Vd)
Equation for the Volume of distribution
Vdist=F*Dose/Cpo; where F is bioavailability and Cpo is plasma concentration time zero.
What is the thereputic concentration line on the conc. vs. time graph?
it indicates the conc. of drug that is needed to be active as intended as a drug in the body.
conceptually how do we find the volume of distribution?
look at the conc. at the begining of the elimination phase extrapulate back to imagine a theoretical plasma concentration time zero and then determine the amount of drug that made it to systemic circulation (bioavailability) and then figure out the total volume that would be needed to contain that amount of drug at that conc.
what is Extraction ratio?
it is first pass metabolism or excretion -- first pass effects.
how do we find Cpo or the plasma concentration time zero in order to find the volume of disttribution?
we look at the elimination phase and then linearly extrapolate that back to the time zero and the concentration that would result is the Cp0
what does Vd actually tell us!!
how widely is the drug distributed out of the plasma -- big volume of distribution would say that the drug is widely distributed throughout the body (esp. to the fat) and a low Vd would say that the drug is mostly in the circulation.
what is the compartment models of a drug
a way to model the loss of a drug that may be to a one compartment or "volume of distribution" or to multiple compartments to model the loss of the drug accuretly in the body. Math: the sum of first order solutions for each compartment (in terms of the nateral number) is the conc. as a function of time.
a measure of the body efficiency in eliminating the drug
how do we express clearence (units)
Expressed as volume of plasma completely cleared of drug per time. (theoretical elimination of the drug piece-wise from the circulation) units of Volume (of plasma cleared)
how would changes in renal function change the clearance
kidney function down--clearence down; kidney function up -- clearence up
what is first order elimination?
it is based on a first order differential equation model: the rate of drug eliniated is proportional to plasma concentration.
what is zero-order elimination of a drug?
the rate of drug elimination is constant and independent of plams concentraton, and there-fore clearence and half life are not meaningful.
what is the clinical significance of saturatinon of first order elimination?
you shift to zero order elimination and the concentratioin of the drug will not fall as quickly so it would be easy to over-dose if you continue to dose!
what happens has you drink alcohol a lot and the later drinks seem to have more effect
moving from first order to zero order elimination!
what is the equation for the conc. of the drug vs. time?
it is the plasma concentration time zero times natural number raised to neg. elimination rate constant times time.
what is the relation between time half life and elimination rate constant?
what is the relation between elimination rate constant and the clearence and volume of distribution?
what is the relation between t1/2 and Vd/CL
t1/2 = ln(2) * Vd/ (CL)
how do I find a total clearence if there are multiple routes to clearence?
just add clearence together.
Is drug elimination half-life = effect half-life?
not at all!!!!
what may affect drug clearance?
organ perfusion and function
what is the goal with a dosing regimen?
to have rate of drug in equal to the rate of drug out so that you will come to equilibrium.
equation for rate of drug in = to rate of drug out i.e. what is the equation for rate of drug in and the equation for rate of drug out (equal to each other)
F*Dose/t = CL * Css where the F is bioavailability and t is dosing interval, and Css is steady state conc. and CL is clearance, TC therapeutic conc. TD is toxic dose.
how many half lives does it take to reach a drug concentration steady state
what is the main affecter of the magnitude of concentration fluctuations?
The dosing interval!! the more often you dose, the smaller the peak conc. will be!