Flashcards in Pharmacokinetics One and Two Deck (37):
What are the basic pharmacokinetics perameters?
Volume of distribution
- Loading Dose
- Maintanence dose
What is pharmacokinetics?
The study of ADME on a quantitative basis
-How drug concentrations change with time from administration
What is the true definition of pharmacokinetics?
Pharmacokinetics is the study of drug concentrations time profile in the body
What is the basic time course of a drug?
(metabolism or) Excretion
What is drug absorption?
Process by which the unchanged drug moves from the site of administration into systemic circulation
What is drug absorption relevant for?
Non-vascular administration (not-intravenous (IV))
- Oral (po)
- Subcutaneous (sc)
- Intramuscular (im)
- Rectal (pr)
What is bioavailibility?
The fraction of unchanged drug that reaches systemic circulation (out of dose administered- some may break down or be excreted-known as first phase effect)
What is the equation for bioavailibility?
F = AUCpo x DOSEiv
AUC = Area under plasma concentration curve vs time
F is constant, so you can change the doseage and to change the AUC, but F will always be the same
What is the first phase effect?
Loss of drug occurring before the drug reaches systemic circulation
What are the three pharmacokinetic parameters?
Volume of distribution
Plasma Clearance (cl)
Plasma half life (T0.5)
What is distribution?
Processes involved in delivery of the drug to the tissues via the arterial blood. (general circulation to tissue)
What defines distribution?
The parameter known as volume of distribution
What is the equation for the volume of distribution?
V = Amount of drug in the body
Plasma drug concentration
What are the determinants for the volume of distribution?
Body mass and composition
Physicochemico properties of the drug
Drug binding to plasma proteins (decreases v)
What is the loading dose?
The first dose a drug treatment, required to reach the target concentration RAPIDLY
What is the equation of LD(mg)?
LD = V(L) x target concentration (mg/L)
Two factors must be known
What is drug elimination?
The irreversible removal of drug from the body
What process can occur to cause drug elimination?
Drug metabolism (conversion of drug into another chemical species)
Drug excretion (loss of drug in bile or urine)
What is the definition of clearance?
Volume of plasma drug cleared per a unit time (L/h)
What is the equation for elimination rate?
CL x concentration = elimination rate
What is the equation for clearance?
Cl= Dose / AUC
What is the definition of maintenance dose(MD)?
Dose rate to achieve and maintain a target concentration
What is steady state?
When dose rate in= rate of elimination
What is the equation for MD?
MD (mg/h) = CL (l/h) x Target concentration (mg/L)
What is half life?
The time required for drug concentration to halve
What does half life depend on?
Volume and clearance
Is half life variable?
Usually constant irrespective of drug concentration
What is the concentration of drug in the body related to?
The number of half lives that have occured since the time of administration
If the half life is known then what is it possible to calculate?
How much drug is left in the body
How long it will take to reach steady state
What is the equation for half life?
T0.5 = 0.7 V/Cl
after four half lifes how much drug will have been eliminated?
more than 90%
What does half lives help predict?
When the therapeutic or toxic drug effect is likely to cease
How many half lives is considered the point where a negligible amount of drug remains in the system?
Four half lives
What is accumulation?
When after repeated dosing or infusion, the drug will accumulate in the body until input rate= elimination rate (steady state)
When does steady state occur?
Drug accumulation is complete(no longer occurring) and concentrations have plateaued (low level of drug)
How many half lives does it usually take to reach steady state?