pharmokinetics Flashcards
wk 10
What is encompassed in pharmacokinetics?
How drugs are:
Absorbed in body fluids
Distributed to sites of action
Metabolised into inactive/active metabolites
Excreted by body
Why is the extent of absorption important?
Determines magnitude of response
and time of onset of action
What are the main routes of administration? And where are they?
Oral
parenteral- injection
inhalation- lungs
epithelial - via a membrane (skin, mucosa, nasal)
sublingual - under tongue
rectal
What are the four types of parenteral routes of administration?
Intravenous (via blood)
intramuscular (into the muscle)
Subcutaneous (under the skin)
intrathecal (into subarachnoid space of spine
What are the two ways that routs of administration can be divided?
Enteral
- into GI tract
-invloing/passing through intsetine
Parenteral
-not into GI tract
What are the chemical factors that affect the degree of GI absorption via oral route?
Formulation
Physical properties
Ionisation
Solubility
What are the physiological factors that affect oral administartion?
PH of GI contents
GI motility
Disorders
Presence of food
What are the advantages of Parenteral (intravenous) route of administration?
most common
-IMMEDIATE effect
-can deliver large amounts over time (infusion)
-used for drugs that can’t be orally taken or needs to be broken by first metabolism.
What are the disadvantages of Parenteral (intravenous) route of administration?
difficult to administer
-potential risk of overdose/ throbosis/ infection
what is an advantage and disadvantage of
Parenteral (Subcutaneous and intramuscular) administartion?
-A = lower rate of absorption and longer drug action
more painful and dependant on local blood flow
What is an example of Parenteral (Subcutaneous and intramuscular) administration?
insulin
What is inhalation only used for which can be a limiting factor of it’s use?
Only used for anesthetics and drugs whose site of action is the lung
What is an example of a drug that uses epithelial administration?
oestrogen patches
What is the advantage of Sublingual administartion?
Rapid absorption directly into systemic circulation without passing through liver
When is rectal administartion used (advantage)?
For drugs that have a local effect on GI tract
or
When intravenous administration is not possible
Why is lipid solubility the most important factor in drug absorption?
because drugs must be able to cross the lipid bilayer to reach their target organ.
What are the characterises of an ionised molecule vs unionsed molecule?
charged polar
water soluble
un-polar and more lipid soluble
What determines the extent of ionisation? Explan
by pH of environment that drug dissolves in.
Drug will be ionised when exposed to a pH opposite to its pKa.
When are acidic drugs more ionised?
in a basic environment: higher pH
Where is most of the drug first distributed to?
organs with a high blood supply.
what does the rate that a drug enters depend on?
permeability of capillaries for drug and perfusion
What is Volume of Distribution?
Volume of fluid needed for drug to be uniformly distributed to produce observed concentration in blood
not a rel volume
What is Volume Distribution determined by?
Relative strength of binding to tissue components VS compared to plasma proteins
(if tightly bound to plasma proteins stay in circulation) V= close to blood volume.
If the drug is tightly bound to tissues…..
= less drug in blood = drug dissolve and large volume
