Pharmacology: Pharmacokinetics II Flashcards
How can you measure drug accumulation?
1/(Fraction lost in one doing interval)
What is the accumulation factor for a drug given once every half life?
2 because (1/(1/2)) = 2
What does the accumulation factor predict?
The ratio of steady state concentration to concentration following the first dose.
How can you predict the peak dose concentration after a new dose during steady state?
It will be equal to (1st dose peak concentration)*(Accumulation Factor)
What does it mean if a drug has high bioavailability?
Drug metabolism is very low and lots of it gets to the blood stream.
How do you calculate bioavailability?
F=f(1-ER) where F=bioavailability, f=gut absorption, and ER = extraction ratio (how much drug the liver destroys)
How long does it take to reach steady state?
4-5 half lives, no matter how much you give
Where should your target concentration be?
Produces at least 1/2 the greatest possible therapeutic effect but no more than 5-10% of patients have toxic effects
How do you calculate the dosing rate?
(CL)(Css) where Css = [drug] at steady state
What does the dosing rate tell you?
How many mg of drug you need to give to make up for what you lose in a day
Normal clearance
(.693 x Vd) / t(1/2)
How do you determine the maintenance dose?
(Dosing rate)(Dosing interval)
When should you consider constant drug infusion?
When the drug half-life < 4 hours or it has extensive first pass hepatic metabolism
How do you calculate how much drug to give a patient that needs that drug immediately?
Loading dose = (Vd)(Target Concentration)
Clearance
(Ke)(Vd) where Ke = elimination rate
