Lec 56: Pharmacokinetics II Flashcards
What are the benefits of administering a constant IV of a drug versus a single oral dose?
- The drug avoids first pass metabolism
2. Drug is more efficiently absorbed into the bloodstream
What are the drawbacks of administering a constant IV of a drug versus a single oral dose?
It takes longer for the drug to reach effective concentration in the blood
Approximately how long does it take for a drug to reach steady state concentration after the first dose (in half lives)?
4-5 half lives
What is the formula for accumulation factor?
Accumulation factor = 1/fraction lost in one dosing interval
If a drug is given once every half-life, what is the accumulation factor?
Accumulation factor = 2
What are the three key things the patient must know about the drugs he/she is prescribed?
- How much
- How often
- What form
What is the therapeutic range of a drug?
The concentration of drug that is in between the maximum safe concentration and the minimum effective concentration
When we prescribe medications why do we aim for between 1/2 the therapeutic range and the minimum therapeutic range? Why not use the whole therapeutic range?
Once the drug concentration goes above half the therapeutic range, side effects are more prevalent
What is the formula for dosing rate? Why is it important?
- Dosing rate = volume of plasma cleared x concentration of drug in that volume
- Dosing rate determines how much drug you should administer/ time (usually in mg/hr) to maintain steady state concentration
If the half life of drug is <4 hours is periodic dosing or constant infusion more appropriate?
constant infusion
What is the formula loading dose? When is it used?
- Loading dose = Volume of distribution x Target concentration
- Essentially just a big dose of a drug that will bring the concentration up to effective levels in a hurry
