Deja Ch 1 Pharmacokinetics Flashcards
Define Pharmacokinetics
Field of study that deals with time required for drug absorption, distribution in the body, metabolism, and method of excretion. In short, it is the body’s effect on the drug.
Define Volume of distribution (Vd)
The apparent volume in the body available to contain the drug. Formula: Vd = Dose/Plasma Drug Concentration
Is Vd a physiologic value?
No
Is Vd an absolute value for any given drug?
No
Define Clearance (CI)
Volume of blood cleared of the drug per unit time; Cl = Rate of elimination of drug/plasma drug concentration; Total Body Cl = Clhepatic + Clrenal + Clpulmonary + Clother
Define Half-life (t1/2)
Half-life (t1/2) Time required for plasma concentration of drug to decrease by one-half after absorption and distribution are complete; t1/2 = (0.693 x Vd)/(Cl)
Define Bioavailability (F)
The fraction of (active) drug that reaches the systemic circulation/site of action after administration by any route; F = (AUCpo)/(AUCiv), where AUCpo and AUCiv are the extravascular and intravenous areas under the plasma concentration versus time curves, respectively
Define Steady state (Css)
Steady state is reached when the rate of drug influx into the body = the rate of drug elimination out of the body; Css = plasma concentration of drug at steady state
How much drug is left after two half-lives?
25%
How much drug is left after three half-lives?
12.50%
During constant infusion, what percent of steady state is reached after one half-life?
50%
During constant infusion, what percent of steady state is reached after two half-lives?
75%
During constant infusion, what percent of steady state is reached after three half-lives?
87.50%
During constant infusion, what percent of steady state is reached after four half-lives?
94%
Give the equation Clearance (Cl)
Cl = K x Vd, where K is the elimination constant
Give the equation Volume of distribution (Vd)
Vd = (LD)/(CSS)
Give the equation Half-life (t1/2)
tl/2 = (0.693)/(K) or (0.693 x Vd)/(Cl)
What happens to the steady state concentration of a drug if the infusion rate is doubled?
Steady state concentration is also doubled; remember that dose and concentration are directly proportional (linear kinetics); Css x k0/Cl
If there is no active secretion or reabsorption, then renal clearance (Clrenal) is equal to what?
Glomerular filtration rate (GFR)
If a drug is protein bound, then Clrenal is equal to what?
GFR _ free fraction (of drug)
What happens to the LD in patients with impaired renal or hepatic function?
Stays the same
What happens to the MD in patients with impaired renal or hepatic function?
Decreases
For each of the following statements, state whether it refers to zero-order elimination or first-order elimination?Rate of elimination is constant, regardless of concentration
Zero-order elimination
For each of the following statements, state whether it refers to zero-order elimination or first-order elimination? Plasma concentration decreases exponentially with time
First-order elimination