Flashcards in Pharmacokinetics 2 Deck (16):
1. What is a dosage regimen?
A plan for drug administration over a period of time. The knowledge of the minimum therapeutic dosage and minimum toxic dosage is taken in to account as well as bioavailability (F), Vd and clearance.
2. What is the maintenance dose and the loading dose?
Maintenance dose → dose required to maintain a certain plasma concentration for the drug over a long period of therapy. Just enough dose is given to make up for the amt lost from the previous dose (Rate of elimination = infusion rate= CL*Css)
Loading dose → dose delivered to reach target plasma level rapidly (loading dose = (Vd*Css)/F) ← for continuous?
3. What is the equation for dosing rate at steady state?
Dosing rate @ ss = elimination rate @ ss = (CL*target concentration)/F
4. What is the calculation for maintenance dose in an intermittent dosing equation?
Maintenance dose = dosing rate * dosing interval
**Dosing intervals will change the peak and troughs of the maintenance dose, but the average will be the same. Frequent dosing intervals is occasionally better because you can remain within he therapeutic window rather than giving a higher amt at lest frequent intervals allowing the pt to deviate in the toxic dose and below the therapeutic dose. With a smaller therapeutic window, give more frequent doses!
5. How would you calculate the daily dose?
Dose per minute*60 minutes/hour *24 hours/day
6. How do you determine the daily dose?
This is determined by the half life of the drug and the minimum therapeutic and minimum toxic plasma concentrations.
7. What is the calculation for finding the IV infusion rate (continuous?) for a drug at steady state?
*note that CL (clearance) is constant for 1st order drugs (most drugs) and the value will be given or found in a table. Because of this Css is directly proportional to the infusion rate. If infusion rate is doubled, Css is doubled.
8. What is a fixed-dose, fixed-time interval regime?
Administration of a drug by fixed dose rather than continuous where the fixed doses result in time-dependent fluctuations in the plasma levels of the drug. (graph with waves that center around steady state/the mean). Repeated intervals
9. What is drug accumulation?
After every dose, a little bit of each dose accumulates in the body and contributes to the steady state plasma concentration. Accumulation is a function of the rugs half life and the dosing interval.
10. What is the accumulation factor (AF)?
The accumulation factor predicts the ratio of the peak concentration at steady state to the peak concentration after the first dose.
AF = 1/fraction lost in one dosing interval
*fraction will be .5 after 1 half life, .75 after 2 half lives, etc
The peak concentration after intermittent doses at steady state is equal to the peak concentration after the 1st dose multiplied by the accumulation factor. [PCss=PC1*AF] ← knowing the accumulation fraction allows you to solve for the dose
11. How would you solve fro the loading dose for intermittent dosing?
Loading dose = Vd*Css ← this will only get you to the steady state plasma concentration, NOT the steady state peak concentration. To match the steady state peak concentration → loading dose = maintenance dose*accumulation factor.
For a given drug, the 1st half life accumulation factor is 2, therefore the loading dose is twice the maintenance dose.
12. How do you change the rate of absorption for oral medication?
Rate of absorption is altered by changing the formulation of the tablets and capsules. Changing the formulation allows for slow and rapid release medications. A slow release formulation leads to a delayed peak, a lower peak and a higher drug plasma at later times. Less frequent administration of a drug is required for a shorter half-life.
13. What is the maintenance dose of an oral medication?
Maintenance dose = (dosing rate/F)*dosing interval
14. What is the time course of a drug effect?
Pharmacokinetics → time course of drug plasma concentration
Pharmacodynamics →drug plasma concentration and resulting pharmacological effect [hyperbolic relationship]
Time course of a drug effect → time course and resulting pharmacological effect
The duration of the drug effect is determined by the drug dose, EC50 and half-life. For first order kinetics, doubling dose will double the drug plasma concentration, so doubling the dose will prolong the drug effect by one-half life.
15. What is the equation (relationship) between drug concentration and drug effect?
E = (Emax*C)/(C+EC50)