Flashcards in 5 lecture Drug Dose Regimens Deck (44):
what is bioavailability?
The fraction of administered drug reaching the systemic circulation in the active form.
What is Vd?
volume of distribution. The apparent volume in which the drug distributes based on the plasma concentration.
what is clearance?
clearance reflects the rate of elimination.
how are most drugs eliminated from the body?
via first order kinetics.
what does it mean to be a first order drug?
Your elimination is dependent on the plasma concentration. This means that it is delivery limited and the clearance rate is constant.
what does it mean to be a zero order drug?
Your elimination is independent of the plasma concentration. This means that it is capacity limited and the clearance rate is variable.
what generally determines the dosing frequency of a drug?
The half life.
What is the therapeutic range?
The therapeutic range is the concentration range of drug that meets the desired affect without being too much (toxic) or too little (ineffective)
what is the lower limit of the therapeutic range called?
the minimum effective concentration
what is Css?
steady state plasma concentration. It gives you an average concentration of the drug in the therapeutic range.
How many doses does it take to get into the therapeutic range?
Generally it takes 3-5 doses.
There are 4 dosing regimens which include?
1) How much (of the drug needs to be given)
2) How often (does the drug need to be given)
3) Route (Oral, IV, etc.)
4) Time (How long will the drug be given)
what is abbreviated as "F"?
Bioavailability. Recall this is the amount of active drug making it into circulation.
which methods have the highest/lowest bioavailability?
IV is highest because all of the drug directly enters the circulatory system.
Oral is lowest because incomplete absorption, first pass effect, etc.
what are some factors affecting bioavailability? (6x)
1) Gastric emptying time (oral)
2) intestinal transit time (oral)
3) First pass effect (oral)
4) Things that inhibit absorption.
5) Degradation of the drug.
6) Blood flow
T/F The area under the curve represents bioavailability of the drug?
How do you calculate the volume of distribution (Vd)?
Vd= amount (drug in the body) / C(plasma)
How do you calculate the amount of drug in the plasma? (Sometimes calls this "amount in the body")
Amount=dose x bioavailability
T/F The Vd of a drug can surpass the total amount of volume within the whole body?
True. This is because many drugs such as chloroquine can be absorbed into fat easily messing up the volume measurement. Ex: Chloroquine=13,000L
Name 4 factors affecting the Vd?
1) weight (body)
3) composition (body such as fat, bone, blood, etc.)
what is clearance?
The elimination of an active drug after its distribution.
how do you calculate clearance?
CL= rate of elimination / C (plasma)
T/F Clearance includes elimination and excretion?
which type of elimination is capacity limited?
0 order reactions
which type of elimination is delivery limited?
1st order reactions
what determines the capacity of an organ to eliminate a drug?
1) metabolic factors: such as quantity/activity of enzymes
2) excretion mechanisms: how much drug is able to be excreted into things such as urine and bile.
which part of the dosing curve gives you the information about the clearance of a drug?
The downward slope gives you information about how quickly the drug is being cleared from the plasma.
which order of drug gives you a fixed % of drug removed per unit of time?
which order of drug gives you a fixed amount of drug removed per unit of time?
which type of elimination (0 or 1st) gives you a straight line when plot Cp on the y axis and time on the x axis?
Zero order because it is a fixed amount of drug per unit time.
what happens to a zero order elimination rxn when it nears its completion of getting rid of the drug in the plasma?
It essentially becomes a first order rxn because it is no longer saturated.
Clearance of a drug depends on 4 major factors which include?
1) body weight
2) blood flow to organs
What is the extraction ratio?
How much of the total drug that a given organ is removing. Ex: if the liver has an extraction ratio of 0.5, it means that the liver is removing/inactivating 50% of all of the drug.
why do you give a loading dose?
The loading dose can bring the plasma concentration into the therapeutic range quicker allowing the drug to have an effect quicker.
How do you determine your loading dose?
DL= Css x Vd / F
DL= Loading dose
Css= Steady state concentration
Vd= Volume of distribution
T/F The loading dose is dependent on the rate of elimination?
1) The loading dose is dependent on Vd and therefore body weight.
2) The maintenance dose is dependent on the rate of elimination.
How do you calculate the maintenance dose?
Dm= Css x CL x dosing interval / F
Dm= maintenance dose
Css= steady state plasma concentration
dosing interval= frequency to give drug
How do you calculate elimination?
Elimination = Cp x CL
Cp= plasma concentration of the drug
Cl= clearance of the drug
About how many half lives of a drug does it take to reach a steady state of the Cp?
about 3-5 half lives
How do you calculate the half life of a drug?
T1/2= 0.693 x Vd / CL
T/F Its always best to give drugs at their half lives?
True. However, if you give the drug more often, you actually get a smoother curve. The reason this is not done is because it becomes a huge pain to give/take it so often.
How does liver disease affect dosing?
decreases CL----->prolongs half life
increases bioavailability (Less broken down taken orally)
decreases plasma proteins. (PP's bind up the drug)
How does kidney disease affect dosing?
Decreases CL------>prolongs half life