Quantitative pharmacokenitics part 2 Flashcards
What type of graph is obtained after administering a sing IV dose?
An expoenetial decay graph
When is only time tou know the amaount of drug injected into a patient?
Straight after injecting it
The larger the volume of drug distributed the shorter the half life. TRUE OR FALSE?
TRUE
What is the equation for exponential decay?
C=C0e-Kt
If we know volume distribution we can calculate the dose for any given concentration. TRUE OR FALSE?
TRUE
What equation can be used to calculate the dose for any given concentration?
Vd=Dose/C0
Doubling the dose does not extend exposure above a certain concentration by t1/2? TRUE OR FALSE?
FALSE
What does K represent?
The fraction of volume distribution that is cleared per min.
What is the equation for rate of elimination?
K=Cl/Vd
Larger volume distribution results in slower elimination . TRUE OR FALSE?
TRUE
WHAT ARE THE TWO FACTORS THAT DETERMINE HOW QUICK A DRUG IS ELIMINATED?
Clearance and volume distribution
What factors control half life?
-Controlled by how much volume of the drug appears to be dissolved in and by what volume of plasma is cleared per unit time.
What are the factors affecting elimination, in terms of Vd and Clearance?
Effects on volume distribution:
- Aging
- Obesity
- Pathologic fluid
Effects on clearnace:
- Cytochrome P450 induction/Inhibition
- Cardiac failure
- Hepatic failure
- Renal failure
What effects do these factors have elimination?
- Aging - decreased distribution
- Obesity - increased distribution
- Pathologic fluid -increased distribution
- Cytochrome P450 induction - increased metabolism
- Cytochrome P450 Inhibition - decreased metabolism
- Cardiac failure - decreased clearance
- Hepatic failure - decreased clearance
- Renal failure - decreased clearance
What is intravenous infusion?
Drug being delivered constanly (i.e via a pump)
What is a loading dose?
Allows us to very rapidly occupy the entire volume of distribution with the drug
What are the pros for Iv infusion?
- Allows precise and controlled exposure
- Adjust concentration
- Stop if required
- Short infusion sometimes used to reduce maximum concentration and adverse events following rapid bolus injection
What is the constant steady state?
Drug concentartion increases to a plateau value
At Css, rate of elimination is equals to rate of infusion. TRUE OR FALSE?
TRUE
What is the equation for rate of infusion?
Rinf= Cl *Css
What is the equation for loading dose?
Css * Vd
How many half lifes does it aproximately take to reach plateau?
3.3 t 1/2
What is plateau concentration determined by?
Infusion rate and clearance
Increasing infusion rate will increase final Css. TRUE OR FALSE?
TRUE
The time taken to reach the plateau depends on half life or rate of elimination. TRUE OR FALSE?
TRUE
What is occured in zero order elimination?
Drug is eliminated at a constant rate and independent of drug concentration
What ocurs in linear pharmacokinetics?
The pharmacokinetics parameters do not change with dose,increasing dose increases exposure
What is non linear pharmacokinetics?
The pharmacokinetic parameters chnage with dose of drug, increasing dose has no effect on exposure
Drugs can be absorbed by either zero order or first order processes. TRUE OR FALSE?
TRUE
What is the equation for the rate of increase of drug in the body?
Rate of absorption - Rate of elimination
Absorption and elimination are comepeting pathways. TRUE OR FALSE?
TRUE
It takes longer for drugs that are administered orally to available in the systemic circulation. TRUE OR FALSE?
TRUE
What occurs dose is increased?
- Increased Cmax and AUC
- There is no effect on Tmax
What occurs to Cmax and Tmax when a drug is given via P.O with food?
Cmax and Tmax are altered
Absorption can become rate limiting when it occurs extremely slowly. TRUE OR FALSE?
TRUE
What controls the rate of absorption?
rate of elimination
What equation can be used to determine the rate of elimination in P.o administration?
Kel=Cl/Vd
What symbol is used to represent bioavailability?
F
What factors can affect bioavailability?
- incomplete absorption
- poor dissolution
- poor permeability
- metabolism before absorption
If the bioavailability of the drug is low, a larger dose can be given, TRUE OR FALSE?
TRUE
What equation can be used to determine the amount of drug reachin systemic circulation?
ARSC= F*Dose
How can we measure bioavailability?
By measuring th AUC
What is required for Css max in a repeated dose?
Needs to be less than the concentration at which toxicity is observed
What is required for Css min in a repeated dose?
Needs to be greater than the concentration required to have a therapeutic effect
How can bioavailbility be determined when when doses are equal?
Bioavailability is the ratio of the two AUC
What is the average constant steady state dependent upon?
Dose and frequency
Why is a loading dose important for drugs that have larger Vd?
Takes longer to reach constant steady state, as drug is being distributed to other parts of the body.
What is a maintenance dose?
once desired plasma drug concentration is achieved, then a maintenance dose compensates for drug elimination
