drug therapy Flashcards
discuss physio-chemical factors that affect the transfer of drugs across cell membranes
molecular size conc gradient thickness of membrane surface area type of transport
factors that affect absorption of a drug from GI tract
gastric emptying
motility
surface area
passive/active transport
medical importance of first pass metabolism
since liver metabolises many drugs, sometimes to an extent that only a small amount of the active drug leaves the liver to circulatory system. the first pass through liver may greatly reduce the bioavailability of the drug
benefits of intravenous medication
being able to control dose and delivery speed
ensuring drug remains in system for longer period of time
benefits of topical medication
fewer GI difficulties risks - diff individuals absorb med at diff rates
fewer risks of abuse
easy to administer
reduced hosp congestion
benefits of inhaled medication
localised to target organ , allowing for lower dose - necessary with systemic delivery , therefore, fewer and less severe adverse effects
processes of Phase 1 and 2 metabolism
phase I = oxidation, reduction or hydrolysis of parent drug, resulting in conversion to polar molecule
phase II = conjugation by coupling drug or metabolites to another molecule
role of cytochrome P450
oxidise substances using iron and able to metabolise a large variety of xenobiotic substances - plants, drugs, pesticides etc
clearance of various compounds
hormone synthesis and breakdown
discuss factors, including drugs, which may inhibit or induce drug metabolism with medically relevant examples
pharmacogenetics
how genes affect the way a person responds to meds
pharmacokinetics
what body does to drug
factors that affect absorption
gastric emptying - slower in older person
motility - reduced for older person
surface area - unchanged
diffusion/active transport -
factors that affect absorptionp
gastric emptying - slower in older person
motility - reduced for older person
surface area - unchanged
diffusion/active transport -
factors affecting distribution
blood volume - reduced by 8% in older person
blood flow - reduced CO
transport proteins - reduced albumin
body mass composition - significant increase in fat by 35% , decrease in lean muscle mass , TBW reduced
vol. distribution of polar drugs is reduced
vol. distribution of lipophilic drugs is increased
factors affecting metabolism
metabolism can happen in kidney, skin, brain and liver (predominantly)
liver blood flow - reduction by 20-50%, reduction in hep. mass
liver clearance - enzymes CYP450 reduced
factors affecting excretion
GFR - glomerular filtration rate
reduced in elderly by 50%, reduction by 60% glom.
pharmacodynamics
what drug does to body
absorption
way drug goes from administration and into the blood
distribution
once drug in blood where is it distributed - pathway
metabolism
how does it chemically alter the drug - activation/inactivation
excretion
way drug moves out of the body
transportation methods of drugs into blood
passive - fat soluble drug, water soluble via aquaporins
facilitated - water soluble (larger) via channel
active - transport system with ATP
bulk / endocytosis - membrane engulfs and passes through
routes of admin.
GI tract - capsules, syrups, tablets
first pass metabolism
drug has to firstly pass through liver to be metabolised before being distributed
happens via portal venous system
bioavailability
from dose how much makes it into the plasma
GTN absorption method
sub-lingually
higher bioavailability
topical administration
fat-soluble drugs
steroids ,
subcutaneous route
fat = not good blood supply (5%)
slow absorption drugs
intramuscular
75% bioavailability
10-15% of blood flow goes to muscle
intravenous
complete bioavailability
elimination
primary organ = kidney
- glomerular filtration - once water soluble can be excreted out
- tubular secretion - blood -> urine
- reabsorption - any molecule in urine -> lipid soluble be put into blood via nephron
also, via skin, breast milk, breathing and bile…
