admin. and elim. Flashcards
define bioavailability
how much of a drug gets through the liver to get an active response
how long does oral administration take?
30-90 minutes
advantages of oral administration?
cheap
easy
when a drug is taken orally, where does it then go?
to the gut (GI system) and then to the liver
how long does IV admin take?
2-3 minutes
what is the bioavailability of oral?
10-50%
what is the bioavailability of IV?
100%
how long does intramuscular and subcutaneous take?
10-20 minutes
how do you administer a drug subcutaneously?
into fat deposition
how do you administer a drug intramuscularly?
into the muscle
quad or deltoid administration
when would you use IM or subcutaneous?
when you want a slower release of the drug but to bypass 1st metabolism of the liver
how long does rectal administration take?
5-10 minutes
how is the drug metabolised rectally?
by the liver via the anterior mesenteric artery
how does inhalation of the drug work?
goes to the lungs then the bloodstream
how does transdermal work?
patches applied to the skin then enters the bloodstream
how does topical work?
applied directly to the skin so it has a local action
how are transdermal and topical different?
transdermal - into bloodstream
topical - local effect
what is sublingual?
under the tongue
why is sublingual administration so fast?
underneath the tongue has such a rich blood supply and it bypasses the liver
how does intranasal work?
into the nose
local or into blood stream
how does intrathecal work
into the cerebrospinal fluid into the ventricular system or into the bloodstream
what is an advantage of intrathecal administration?
bypasses the BBB to allow drugs to work on the brain
what is epidural administration?
outside of the spinal dura
when is epidural administration used?
local anaesthetic for peripheral nerve and spinal nerve
where does intraarticular administration go?
into the joint space
what is the fastest route of administration?
IV
what are the slowest routes of administration
IM and oral
how do drugs go from the GI tract to the liver?
portal vein
where does first pass metabolism occur?
gut and liver
what is first pass metabolism?
when the concentration of the drug is greatly reduced before it reaches the systemic circulation
what is a pro-drug?
a biological inactive parent drug that requires a chemical or enzymatic transformation to release active drug
Where are pro-drugs converted into the active form?
The liver
how are pro-drugs converted into the active form?
liver enzymes cleaves off the carrier molecule, activating the drug rather than the drug just being digested
what is the purpose of pro-drugs?
protecting the drug from first pass metabolism in the liver
give an example of a pro-drug and how it works
L-dopa - used to treat Parkinsons
As a protected molecule it can cross the BBB
advantage of using L-dopa as a prodrug?
smaller dose given which is safer
explain how pro-drugs are used in cancer medication?
tumour specific gene delivery
enzyme expression so that prodrug can bind
toxic drug is given as a prodrug and only targets cancer cells which have the enzyme
cytotoxic drug kills the tumour cell
cell dies and drug goes to neighbouring drugs - bystander effect
what are the two categories of reactions that happen in the liver?
phase 1 and 2
what happens in phase 1 liver reactions?
biotransformation to make drug more water soluble so it can be excreted.
name examples of reactions that happen in phase 1 reactions?
oxidation
hydrolysis
reduction
what happens in phase 2 reactions?
synthesis reactions to become more water soluble
name examples of reactions that happen in phase 2 reactions?
conjugation with glycine, sulfate, glucuronic acid
name the methods of eliminating a drug?
renal hepatic breathing sweating urine fecal
what is the main metabolic organ?
the liver
what things can happen to a metabolite that leaves the bile via the liver?
excreted in the kidneys
reabsorbed and go back to the liver
what is clearance?
rate of elimination in relation to drug concentration in the plasma
how is clearance calculated?
rate of elimination divided by concentration remaining
define half life of a drug
time taken for plasma concentration to reduce to half its original concentration
how is half life calculated?
volume of distribution divided by clearance x0.7
define zero order elimination
the elimination of a constant quantity of a drug per unit time
define first order elimination
the elimination of a constant fraction per unit time
which order of elimination do most drugs use?
first
how many half lives does it take for a drug to be removed from the body?
5
what is the therapeutic window?
where a drug has therapeutic effects
what is the lag period?
the time before therapeutic effect - time for absorption to happen and drug to get into circulation
what is the safe range of a drug?
between the minimum therapeutic concentration and the minimum toxic concentration
before how many half lives will accumulation occur?
4
what is a loading dose?
a larger dose given to get into the therapeutic range quicker
what is a maintenance dose?
maintains the drug in the therapeutic window
what factors effect drug metabolism?
ethnicity age gender diet environment drug interactions diseases
