Drug Metabolism Flashcards
What are lipophilic drugs
Drugs that are soluble in fats oils and organic solvents
How does the CNS affect distribution of drug
It causes rapid distribution
How does the CNS cause rapid distribution of drugs
It has efficient blood flow
Give an example of CNS rapid distribution of drug in action
Anaesthesia working as soon as it hits the systemic circulation
Hours after drug transfer what happens to the remainder
Little of the drug remains in the blood and large amount will be stored in the fat
What does the fat act as in relation to drugs
Storage
How does fat act as a drug storage
It removes the drug from the blood and shorten its action
What happens if the fat store is full and a second dose of drug is given
The drug will not be removed from bloodstream to be stored in the fat. It will stay in the bloodstream and it will exert its action which leads to toxicity
What transfer barriers are present in the CNS
Blood-brain and blood-cerebrospinal fluid barriers
What do the CNS barriers allow
They allow for lipid soluble drugs
What drug isn’t accepted by CNS barriers
Penicillin
What makes penicillin hard to enter the cerebrospinal fluid
It has poor penetration unlike with the body’s their tissues where it diffuses well
When would penicillin be able to enter the cerebrospinal fluid (potentially)
When the meninges are inflamed
What Parkinson’s disease medication can’t e giving directly into the CNS
Dopamine
What form is dopamine given in
Levodopa
How does levodopa enter the brain
It is changed into dopamine by an enzyme
What is a transfer barrier in relation to pregnancy
The placenta
What does the placenta provide a barrier to
The mother and foetus
Why must drug administrator be careful with for the foetus
The foetus kidney and liver can’t metabolise drugs.
Why is it beneficial for drugs to be lipid soluble
In order to diffuse across membranes
Why must the lipid solubility of a drug be higher than the water solubility of the drug
The higher the lipid solubility, the quicker the drug we dissolve into tissues
What happens when lipid soluble drugs pass through the kidney
They are reabsorrbed at the distal tubule and returned to the plasma
How does the body excrete drugs
The body metabolises them to be more water soluble and then creates them in urine
What does the rate of metabolism of a drug determine
The duration of the action of a drug.
What is the main site of drug metabolism
Liver
What other sites aid in drug metabolism
Kidneys,lungs, blood and intestines
What influences the rate of metabolism
Enzymes
How do enzymes influence the rate of metabolism
Enzyme activity can either increase or decrease the metabolism of drugs
