3) Pharmacokinetics and Pharmacodynamics Flashcards
(19 cards)
What is Bioavailability (F) ?
The fraction of drug which reaches circulation unaffected.
IV drug = 100%
What factors can affect F
> Absorption - Formulation - Age (Luminal Changes) - Food - Vomiting / Malabsorption > 1st Pass Metabolism Drug metabolised before reaching systemic circulation
What factors can affect protein binding of drugs ?
> Hypoalbuminaemia
Pregnancy
Renal Failure
What are factors that can affect therapeutic agents ?
> Blood flow > Capillary Structure > Lipophilicity / Hydrophilicity > Protein Binding > Volume of Distribution
What is Volume of Distribution ?
A measure of how far the drug will distribute in the body.
Small Vd = Drug is confine to plasma and extracellular fluid
Large Vd = Drug is distributed throughout tissue
Vd = Dose / [Drug]plasma
What factors can affect Vd ?
> Weight - Drugs can travel through fat better, meaning there is less drug in the plasma > Blood Flow > Drug Interactions > Receptor Sites.
What does Phase I enzymes do in metabolism ?
They carry out the first step of metabolism in the liver. Usually carried out by CYP450 enzymes > Oxidation > Dealkylation > Reduction > Hydrolysis
What does Phase II enzymes do in metabolism
They add components such as: > Sulfates > Glutathione > Glucuronide > N - Acetyl
What factors can affect Metabolism of a drug
> Inhibition of CYP450 enzymes such as grape fruit - Drugs last longer > Liver Disease > Age > Hepatic Sate > Alcohol
What are pro drugs ?
Drugs that are activated when they are metabolised
e.g. Codeine -> Morphine
What are the different routes for the Elimination of Drugs ?
> Kidney (Major) > Fluids - Sweats - Tears - Genital Secretions - Saliva - Breast Milk > Solid - Faeces - Hair > Gases
What factors affect Elimination of a drug ?
> Renal Disease
-> Reduced GFR
Hepatic Disease
-> Reduced Liver Activity = Less metabolism so less elimination
Cardiac Disease
-> Reduced Organ Perfusion to liver and kidney
What 3 processes affect Kidney Elimination ?
1) GFR
2) Tubular Secretion
3) Tubular Re absorption
What is a Half Life ?
The amount of time it takes for the concentration of the drug to reduce by half.
t1/2 = 0.693 x Vd / Cl
Describe First Order Kinetics
Rate of Elimination is proportional to the Drug Level
Half life can be easily be determined.
(Most Drugs exhibit first order kinetics at therapeutic doses)
Describe Zero Order Kinetics
Rate of Elimination of constant
(At high enough concentrations all drugs exhibit at high [])
These drugs are more likely to result in toxicity b/c you are now unable calculate their t 1/2
How many half lives is required before a steady state is reached ?
4 / 5
What is a steady state (Css)
When the plasma concentration is in the therapeutic window
How can we achieve the steady state of a drug without waiting for 4 / 5 half lives ?
Give a loading dose,this is when you give a larger dose than normal for the first few times
Loading dose = Vd x [Drug] Target
