Topic 9 - Pharmacokinetics of Elimination Flashcards
Renal vs Hepatic Metabolism
Renal Metabolism does not change the drug
Hepatic Metabolism turns drug into a different metabolite
This metabolite may still be active
What order is a drug elimination graph
First Order
Exponential Decay Graph
How does concentration impact elimination
The higher the concentration the more rapid the drug elimination
What does the elimination rate constant (kel) tell us?
The fraction of plasma volume that is cleared of drug in a unit of time
kel = 0.5/hour means that 0.5 L of 1L plasma is cleared of drug
0.5 * 100 = 50%
Every hour 50% of 1L is eliminated
1L is the AVd
Elimination Half Life Formula
t1/2 = ln(2)/kel
Tells us how much time it takes to reach half life
Drug loss in tissue vs blood (What is the relationship)
It is proportional
If the tissues lose half of the drugs present then the blood will also lose half of the drugs present
What is Clearance
Volume of plasma that is cleared of drug in a unit of time
What kinds of drugs would have a high clearance rate
Drugs that are rapidly metabolized or rapidly eliminated by kidneys
What does AVd tell us specifically?
How distributed a drug is in a theoretical volume of plasma
What does a high AVd mean?
Drug is extensively distributed in the tissues, little drug in systemic circulation
Clearance Formula
Cl = kel x AVd
Fraction of plasma that is cleared x Volume that Drug has distributed into
Solving Clearance Problems (Half Life is given, AVd is given)
Obtain Kel using half life
Kel = ln(2)/t(1/2)
Multiply Kel with AVd
