Anatomy and physiology - Pharmacokinetics Flashcards
What is pharmokinetics?
What the body does to drugs
What is lignocaine and what does it do?
A local anaesthetic that blocks sodium channels which stops action potentials and causes local anaesthesia
What is intravenous administration?
injected directly into the bloodstream so reaches the site immediately
hat is an issue with intravenous administration (IV)
There are sodium channels everywhere, so high concentrations can cease activity everywhere
What is a benefit of intravenous administration (IV) other other forms of administration?
All the drug is rapidly absorbed, whereas others and slower and incomplete absorption due to factors such as first pass metabolism
What determines plasma concentration?
Dose, elimination, and route of administration
What determines the effect of a drug?
Number of receptors bound to drugs, which depends on drug concentration which depends on plasma concentration
How do you calculate therepatuic index?
toxic dose/therapeutic dose
What does ED50 mean?
ose that produces therapeutic effect in 50% of the sample
What does LD50 mean?
Dose that kills 50% of the sample
What does Emax mean?
Dose that produces the maximum response of a drug
What is local concentration?
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What four areas of pharmacokinetics determine what happens to a drug in the body?
Absporption
distrubtion
metabolism
elimination
What determines tissue drug concentrations?
Dose, amount and rate
What determines absorption?
Route of administration
Solubility, physical form
What determines elimination?
Renal and hepatic clearance
interactions
What group of enzymes mainly chemically modify the drugs in the liver?
Cytochrome oxidase P450
What happens to the drug in the liver?
Oxidation/reduction or conjugation to make it excretable, resulting in active or inactive metabolitaes
What are the requirmetns for elimination of drigs?
functioning liver and enzymes
What is enzyme inhibition?
A drug inhibits the enzyme so the other drug isnt cleared to quickly and plasma concetration stays high for lomger e.g. grapefruit juice interferes with a number of drugs
What is enzyme inducition?
ne drug increase the rate of clearance of another drug meaning the given dose is less effective
ow are drugs elimnated from the body and what factors depend on it?
Drug is filtered by the kidney into urine, which depends on the natrure of the drug and functioning of the kidneys; the elderly have impared renal function
How is rate of elimination calculated?
Rate of elimination in (mg min-1) = Ctotal x plasma
How is C total in the clearance formula calculated?
Clearance of the renal + hepatic clearance
What is plasma half loife?
The time taken for plasma concentration to drop by half (after drug adminisatratioh has ceased)
What is bioavailabiliyty?
the proportion of a drug that has an active effect when introduced into the body
How to calculate bioavailablity?
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What is first pass metabolism?
he rapid uptake of an activr compound imto inactive compounds by the liver
Does first pass metabolism apply to intravenous drugs?
Intravenous injections bypass absorption barriers and first pass metabolism
Drugs in the blood travel from small intestine to liver via which blood vessel?
hepatic portal vein
What is a prodrug?
A drug that is inactive until activate by metabolic or physico-chemical transformation
hat happens to drugs when they are metabolised in the liver?
A prodrug will become an active drug
A drug will become less ative or deactivated
How does patient size affect concentration?
Smaller patients have less volume so a dose will have a larger tissue concentration, therefore paediatric doses tend to be caclulated by patient weight
How will plasma concentration differ with i.m?
eak is later and a lower maximum concentration which may be beneficial
What is an isotonicn solution and why should fluids be isotonic?
hen the fluid has a similar concentration as blood. To increase fluid volume, without any shift from high to low or vice versa
When and how is 0.9% sodium chloride administered?
Supplies water and salt to the body
When and how is 5% dextrose administered?
hypotonic solution which is a form of glucose that replaces lost fluids
How does chemical property affect absorption?
Drugs must be either water or lipid soluble
Highly polar drugs cannot pass through the membrane of GI tract so not absorbed (so must be given IV)
Neuropharmacological agenst must be able to cross blood brain barrier
How does physical form affect absorption?
Smaller particles dissolve more rapidly
Tablets must disintegrate, but can also be a good thing such as modified release tablets
How does metabolism affect absorption?
ontact time at absorption site
Total surface area for absoprtion
blood flow to site
drugs like diazepan and diamorhine are activated by metabolsim
so metablotices like lognocaine are toxic
What factors affect ditribution?
Blood brain barrier
differnet solubility
How do ionic properties affect distribtion?
Strong alkaline drugs are poorly absorbed in stomach
acid drugs become trapped in alkaline environments
What is the aim of drug administarion?
To get the drug into circulation
To administer it locally
What does p.r stand for?
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What does s.I stand for?
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What does s.c stand for?
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What does i.m stand for?
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What does i.v stand for?
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What is the negativity of oral administartion?
Slowest, around half hour
What is transdermal administrtion?
The drug is absorbed through the skin over several hours
