Factors affecting drug metabolism Flashcards
What is enterohepatic circulation?
Recirculating of bile salts, drugs and their metabolites via biliary excretion and reabsorption in the intestine that can maintain drug plasma concentration.
What is first order kinetics?
Doubling the concentration of the drug doubles the reaction rate
What is zero order kinetics?
Reaction rate is always the same irrespective of drug concentration.
What is non-linear kinetics?
Reaction rate increases with drug concentration until enzymes are saturated and rate reaches a constant.
What is the therapeutic range?
Dosage range/plasma concentration expected to achieve the desired therapeutic effect.
what is the effect of first order kinetics on drug elimination?
Constant half life
Drug is being eliminated at a constant proportion per unit time.
What is the effect of zero order kinetics on drug elimination?
A constant amount of drug is eliminated per unit time.
It can take longer for a drug to reach 50% from 100%.
What is the affect of enzyme inhibition?
Decreased enzyme activity = reduced metabolism of substrate drugs = higher plasma concentration = more efficacy/toxicity
What is the affect of enzyme induction?
Enzyme activity is increased = increased rate of metabolism for the substrate drugs = lower plasma concentration = less efficacy/ toxicity
What is the mechanism of enzyme induction?
Through increased happened and protein expression
It has a slow onset & offset.
What is the mechanism of enzyme inhibition?
Same principles, competitive, non-competitive and uncompetitive.
Has more of a rapid onset/offset. It can be reversible so the offset can be slower.
What are the factors affecting drug metabolism (cytochrome P450)?
Age Pregnancy Smoking Alcohol and foods Genetics Kidney or liver disease Drugs
How is the therapeutic index calculated?
TD50/ED50
ED50 = Dose at which we have there is 50% efficacy
TD50 = dose at 50% toxicity
Bigger therapeutic index = wider difference between efficacy and toxicity
What is the therapeutic window?
Dose at which we have good benefit before there is a toxic effect/ or little toxic effect.
