Parameters of PharmacoKINETICS Flashcards
Parameters of Pharmacokinetics:
- Volume Distribution Vd
- Total Body Clearance CI
- Half-Life
– most important parameter
Volume of distribution (Vd)
- quantitative estimate of tissue localization of the drug over the concentration of the drug in plasma
Volume of distribution (Vd)
Formula for Vd:
Vd =
total amount of drug in body (site of action)
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concentration of drug in plasma (bound form)
– plasma/blood is effectively cleared of the drugs in specified unit of time by the kidneys
Total Body Clearance (Cl)
Formula for CI:
Cl = Vd x constant (ke)
= Vd x 0.0693
t ½
Formula for CI:
Cl = Vd x constant (ke)
= Vd x 0.0693
t ½
fraction of drug entering compartment per unit time
*Ka – absorption rate constant
fraction of drug eliminated from compartment per unit time
*Ke – elimination rate constant
– time it takes for ½ of the drug to be eliminated at constant rate of 0.0693 t ½
Half-Life
- time required for plasma concentration of a drug to decrease by 50% after discontinuance of the drug
Half-Life
reflects rapid decline in plasma conc. of drugs as the dose of drug is distributed throughout the body
distribution half-life (t ½ alpha)
– reflect slower metabolism and excretion of the drug
elimination half-life (t ½ beta)
– measurement used in evaluating the safety and usefulness/effectiveness of the drugs
Therapeutic Index (TI)
or
Margin of Safety
- pertains to relationship between doses of drug required to produced undesired and desired effects
Therapeutic Index (TI) or Margin of Safety
