Chapter 3: Pharmacokinetics Flashcards
Often used as a synonym for pharmacokinetics; the processes of drug absorption, distribution, and elimination. Sometimes used more narrowly to describe elimination
Biodisposition
In pharmacokinetics, the condition in which the average total amount of drug in the body does not change over multiple dosing cycles (ie, the condition in which the rate of drug elimination equals the rate of administration)
Steady state
The elimination of drug that occurs after administration but before it enters the systemic circulation (eg, during passage through the gut wall, portal circulation, and liver for an orally administered drug)
First-pass effect, presystemic elimination
The plasma drug concentration below which a patient’s response is too small for clinical benefit
Minimum effective concentration (MEC)
The maximum and minimum drug concentrations achieved during repeated dosing cycles
Peak and trough concentrations
The graphic area under a plot of drug concentration versus time after a single dose or during a single dosing interval. Units: concentration × time; eg, mg min/mL
Area under the curve (AUC)
The fraction (or percentage) of the administered dose of drug that reaches the systemic circulation
Bioavailability (F)
The time required for the amount of drug in the body or blood to fall by 50%. For drugs eliminated by first-order kinetics, this number is a constant regardless of the concentration. Units: time
Half-life (t1/2)
```
t1/2 = 0.693×Vd / CL
Units = Time
~~~
The ratio of the rate of elimination of a drug to the concentration of the drug in the plasma or blood. Units: volume/time, eg, mL/min or L/h
Clearance (CL)
Clearance (CL) =
Rate of elimination / Plasma concentration (Cp)
The ratio of the amount of drug in the body to the drug concentration in the plasma or blood. Units: liters
Volume of distribution (apparent) (Vd)
For a drug eliminated with _____, clearance is a constant; that is, the ratio of rate of elimination to plasma concentration is the same over a broad range of plasma concentration
First-order kinetics
Elimination rate is constant and clearance is not constant.
Zero-order kinetics
The effect of a drug at 87–90% of its steady-state concentration is clinically indistinguishable from the steady-state effect; thus, _____ half-lives of dosing at a constant rate are consid- ered adequate to produce the effect to be expected at steady state.
3-4 Half-lives
Dosing rate = CL × Desired plasma concentratition / Bioavailability
Maintenance Dosage
_____ = Vd × Desired plasma concentration / Bioavailability
Loading dose
