Pharmokinectics Flashcards
What is a maximum effective concentration?
a concentration for which when you increase it, you get no greater response or can get a toxic reaction
What is first order kinetics? What is true about drug elimination in this situation?
the rate of drug elimination (also called disposition) is proportional to the drug concentration.
-the fraction of drug eliminated in the body per unit time remains constant
What is the volume of distribution equation? variations of equation? Definition? units? how should you think about it ?
- Vd= amount of drug in the body/ plasma drug concentration.
- Defined as the theoretical volume occupied by the total absorbed drug amount at the plasma concentration.
- L or ml-
- size of an imaginary container that is required to account for the total amount of the drug in the body
- Vd= bioavailability*dose/(initital plasma concentration at time 0)
What is the absorption rate constant? abbreviation?
- Ka
- fraction of the administered dose that leaves the site of administration per unit time.
- the larger the Ka, the faster drug is absorbed.
What is zero order absorption rate? abbreviation? units? what type of administration? Same for first order?
- Zero Order: absorption rate is constant, indepedent of amount of drug administered.
- Ko
- Units: Mg/min or mg/ml/min
- Form of admin: IV
First order: absorption rate is proportional to the amount of drug present (ka)
- fraction of drug absorbed per unit of time
- larger the Ka, faster drug is absorbed
What is Ro? (r sub o)
rate of drug infusion in amount per unit time
What is zero order elimination? Units? What is first order elimination? what is K and what is it equal to?
- zero order: the amount od drug (A) eliminated at a constant rate. Concentration (c) eliminated at a constant rate. Units: mg/hr or mg/ml/hr
- First order: amount of drug (A) eliminated at a rate proportional to the amount of drug remaining. K is a constant that relates the rate of drug elminated to the amount in the body at any time.
- K= rate of elmination/ amount of drug in the body
What are drugs eliminated according to first order vs zero order kinetics? What is molecular burden and how does it relate to this?
- drug enter the liver and begins to be metabolized by CYP enzymes. As more drug mol are presented, more bind to CYP enzymes and rate of elimination increases (first order because rate is prop to drug con)
- When CYP enzymes become saturated, you are now in zero order (independent of drug con)
- molecular burden= # of drug moleculesd
- drug that biotransform slowly cannot tolerate a high molecular burden (zero order)
- drug that biotransform w/ low potency require a high dose, or high molecular burden, as such are zero order
What is the key difference between elimination rate and clearance? What equation relates the two variables?
- elimination rate describes the mass of drug eliminated per unit time while clearance is the volume of blood that drug occupies
- rate of elimination (mg/min)= Clearance (ml/min)*concentration (mg/ml)
What is the clearance equation? Units?
- Cl= Dose/AUC
- (Mg/mg/(ml/min))= ml/min
What is AUC? What is it used to estimate? What equation will you use for IV doses? Other doses?
- area under the curve
- estimating bioavailability of drugs and estimating total clearance of drugs
- AUC= dose/Cl (IV)
- AUC= F*(dose)/Cl (non IV to account for lack of absorption)
What is the equation for elimination rate? what is K?
- rate of drug elimination= K* (amount of drug in the body)
- K = rate of drug elimination/ amount of drug in the body (fractional rate of drug removal per unit time)
- units: k= mg/min//mg
What is the equation for half life?
- t(1/2)= (0.7* Vd)/ Cl
- Vd= volume of distribution
- Cl: clearance
What is steady state? Equation? What is it independent and dependent of?
- Steady state: condition of equilibrium in which the rate of administration equals the rate of elimination. Reached after 5-half lives have elapsed
- % of steady state achieved= 100* (1-(1/2^n)) where n is number of half lives elapsed
- independent: dose or rout of administration
- dependent: half life
What is a loading dose? Why is it used? What is the equation? units?
-it takes 5 half lives to reach steady state. If you need an immediate drug response, you can achieve therapeutic concentration immediately by giving a large dose initially followed by smaller maintenance doses (MD).
-Loading dose= Css* Vd/(F)
(steady state concentration* volume of distribution/ (bioavailiability))
-mg
