9 metabolism of analgesics Flashcards
what is the fraction absorbed
the initial dose that appears in the portal veins
what defines the bioavailability
the fraction reaching the blood circulation after the first pass through the liver
what needs to happen for any analgesic to have its desired action
it needs to be in the therapeutic window
how does the body process the concentration of drug
by metabolism using the liver
what is the overall aim of drug metabolism
to break down drug into metabolites which can be excreted more easily
what does increasing water solubility of drugs do
aid excretions
phase 1 and 2 of excretion
- activation by oxidation, reduction and hydrolysis. introduce or expose a functional handle for phase 2
- conjugation to make more polar molecules
do drugs metabolise by phase 1 or 2
can be a mix of both
do each drug have their own individual route for metabolism
yes
where are cytochrome P450 found
in mitochondria or endoplasmic reticulum of cells
what is the most important phase 1 metabolic pathway
the cytochrome P450 system
why is it important to understand the cytochrome P450 system
- can be inhibited by different drugs
- can be induced by different drugs
- presence differs across population and age groups
- many different forms (polymorphism)
is there different forms of CYP450
yes, each encoded by a specific gene
what do each different form of CYP450 do
catalyse different classes of drugs
what do most drugs undergo
deactivation by CYPs either directly or by facilitated excretion
can CYPs convert drugs into their active form
yes
do drugs which effect CYP activity effect the metabolic rate and plasma concentrations
yes therefore impacts therapeutic effects of any coadministered drugs
what factors affect CYP metabolism
- polymorphism
- concomitant medication
- genetic variation
- age difference
what does polymorphism cause
drug-drug interactions
what is the largest cause of drug-drug interactions
CYP450 phase 1 metabolism
where does the drug bind to CYP450
close to the haem
why do you need to check how each drug is metabolised
incase they interact with each other
are some people deficient in CYP450
yes so care is needed when prescribing drugs
why is care needed when prescribing to older patients in regards to metabolism
as you get older you are less efficient at metabolising and eliminating drugs
