Drug Clearance and Elimination Half-Life Flashcards
What element in Pharmacokinetics is Elimination associated with?
-Excretion
What is drug Elimination/Excretion?
-Removal of the drug
What is drug Half Life?
-Is the time taken for half the quantity/concentration to reduce from its initial value
What is used to calculate a drug’s Steady State?
-Half-Life
What is Steady State?
where the rate of drug administration=elimination/output
What is the main organ that carries out drug elimination?
- Kidney
- Via Renal Filtration
What is calculated to express drug clearance?
Clearance (CL) -volume of plasma cleared of a drug over a specified time period
Describe the effects of different drug concentrations
Low-Sub-Therapeutic Effects
Medium-Therapeutic Effect
High- More toxic-adverse drug reaction (too many toxic metabolites)
Does absorption and Elimination occur at the same time?
- Yes
- Associated with Steady State (SS)
Why does a drug’s plasma concentration decrease after passing through the liver?
-Phase 1 and Phase 2 metabolism taken place
What is Total Clearance Tc?
-Describes Elimination route of a drug but by several routes NOT one
What is the Clearance Rate formula?
CL=Rate of Drug Elimination/ [Drug]plasma
What is First Order Kinetics?
-Reaction rate is directly proportionate to concentration of reactants (e.g drugs)
What is Zero Order Kinetics?
-Elimination rate has reached its Vmax-max reaction rate
How does the elimination rate reach its Vmax in Zero Order Kinetics
- Elimination Mechanisms are now saturated (full)
What does the Michaelis-Menten Equation calculate?
- Rate Equation (Re) in a reaction
- Shows Elimination rate
Why is Clearance calculated in the Pharmaceutical Industries?
- Helps calculate how to get Steady State
- Drug administration- elimination of drug
What is Elimination Half-Life?
- Amount of time it takes for the blood plasma concentration of the drug to decrease by half
- Usually X5 Half-lives meet Steady State (SS)
What x2 factors does Elimination Half Life rely on?
-CL and Vd
How does CL effect Elimination Half Life?
- CL Increases- Half life deceases because drug being eliminated faster
- CL Decreases-Half-Life increases
How does Vd effect Elimination half life?
Vd Increases- Half life increases as more spread out drug stays for longer
Vd Decreases-Half Life decreases
What is the formula for calculating Half Life?
t1/2= 0.693 xVd
CL
What factors can effect CL?
- Types failure-cardiac, renal, hepatic-as metabolism here etc
- P450 Enzyme System
What is Hepatic Failure?
- Liver failure
- Affects Phase 1 and 2 metabolism
What can ageing affect?
-Volume Distribution
