Administration . Absorption and Distribution of Drugs Flashcards
Pharmacokinetics is …
How the body affects a specific drug after administration
Draw and lablel the pharmacokinetic curve
Briefly explain what is happening at each interval
Refer to Notes
The administration of drugs can be classified into different groups . What are they?
Enteral
Parenteral
A drug that is administered via the enteral route involves ..
Mouth oesophagus stomach small and large intestines constituents of the GI tract
A drug that is administered via the parenteral route involves ..
may cross epithelium if applied topically to skin
or may avoid epithelium through inhalation and absorbed by lungs or forms of injections
State the enteral routes of administration
sublingual
oral
buccal
rectal
state the parenteral routes of administration
injections
inhalations
cutaneous
What is an intrathecal injection
an injection into the spinal canal or into subarachnoid space so it reaches the cerebrospinal fluid
what is an intraperitoneal injection
an injection made into the body cavity - LBP pts
discuss what you know about the sublingual route of administration
sublingual means under the tongue
involves placing pill or spray under the tongue and floor of oral cavity
connective tissue in this area is highly perfused which means drug only has to interact with these enzymes - liver is bypassed
rapid means of absorption
ideal for emergency conditions like use of GTN for rapid relief of sx of angina
Discuss what you know about the buccal route of administration
buccal means between pts cheeck and gum - not swallowed
liver bypassed
presence of saliva help breakdown of drug
taste may not be nice
What is meant by the first pass effect ?
a concept where conc of drug avail to reach the systemic circulation is reduced due to processes it undergoes like metabolism
Cirrhosis is
Cirrhosis is the severe scarring of the liver and poor liver function The scarring is most often caused by long-term exposure to toxins such as alcohol or viral infections.
Draw and label a diagram of the hepatic portal system
Refer to notes
What does the hepatic portal system do
carries blood from parts of the GI tract to the liver
Give examples of oral drug forms
Capsules - less compressed together , shell of capsule dissolves then contents free
tablets - compressed - disintegrates into smaller
pills
enteric coatings - barrier applied to tablet to protect t from the acidity of the stomach , in other conditions able to break down
elixirs - active ingredient mixed with liquid
suspensions - liquid with small pieces of drug. drug is not completely dissolved in drug
Briefly discuss what you know about the rectal form of drug administration
end of GI tract using suppository
absorbed by the rectums blood vessels
useful for vomiting patients unable to keep anything down
surface area avail for absorption is reduced - no microvilli
allows some bypassing of the first pass effect because venous drainage in this area done by inferior and middle rectal vein with minimal help from hepatic porta system
state the factors which influence absorption of drugs in the GI tract
- Surface Area
- PH of gastro intestinal contents
- Active transport
- Plasma protein binding
- Gastric emptying
- blood flow
- formulation
PH of gastro intestinal contents
the PH conditions will affect the ionisation of molecules
ionisation is process by which molecules that lose electron gain positive charge and molecules that gain electron gain a negative charge.
- mucosa lining of GI tract - impermeable to ionised molecules
- acidic drugs –> acidic conditions of stomach stay in un ionised formed and absorbed in stomach
Surface Area
small intestine - high conc of microvilli so has larger surface area 1000x more than of stomach - absorption more efficient in areas of great SA
Gastric emptying
Related to how fast drug/food leaves the stomach . If drug moves quickly absorption will be reduced
Blood flow
intestine - good blood flow- maintains conc gradient . Drug moves from high to low conc
BF to intestine is greater than stomach - absorption favoured here
Plasma Protein Binding
drug molecules may bind to plasma protein and if occurs it will become inactive .
only free drug molecules can be pharmacologically active
Formulation
small particle size - faster rate of absorption
large particle size - delayers absorption
Active Transport
Transportation of molecules across membranes ( passive or active )
What is an intravenous injection
substance that is given directly into vein
all of it enters systemic circulation
useful for quick rapid response
Disadvantages of intravenous injection
requires trained personnel
sometimes difficult to find vein
expensive ( sterility / cost of preparation and transport/storage)
what is a subcutaneous injection
substance administered into the subcutis layer
often used to deliver vac and meds ( insulin)
layer has few BV - slows absorption - massage to help
to maintains effect locally - vasoconstriction ( painful / finding site for repeated injection can be issue)
what is an intramuscular injection
substance given directly into muscle
lots of BV - faster absorption
used to deliver large volume of meds - antipsychotic drugs - lasting effects
- requires trained personnel
sites for intramuscular injection depend on what?
pts age
type of drug
volume
state the different sites for intramuscular injections
deltoid muscle of arm - small volume
vastus lateralis - newborns and infants
ventrogluteal - pts lying on side ( most comf and safe for adults )
dorsogluteal (less likely to be used due to proximity to sciatic nerve) last resort in adults.
Explain the inhalation route of administration of a drug
pt inhales - lung , has a large SA and BF rapid absorption
bypasses liver and first pass effect
absorption of gasses relatively efficient - Larger particle size = less absorption and more local action, small particle size = favours systemic absorption
What is absorption ?
transfer of drug from site of administration into the blood stream
in order for a drug to get into the bloodstream what does it have to cross
several semi permeable membranes
what is a cell membrane made up of
phospholipid bilayer
- hydrophillic heads - phosphate
- hydrophobic tails - two fatty acid chains
- layer is 10nm thick
how do small molecules cross cell membranes
- forces that hold the CM - weak - drugs may be able to slip through lipids in bilayer . Can only happen if drug is small , lipid soluble and lipophilic
- some drugs may need help so travel through aqueous pores
- specific molecules may recognise certain drugs and help them cross using carrier molecules
passively ( s energy) or actively - pinoocytosis
what do you know about diffusion
passive process requires conc gradient particle size - small membrane - permeable ability of drug to pass through membrane depends on lipid solubility
what is lipid solubility
ability of drug to dissolve in lipid
what is facilitated diffusion
drug molecules combine with carrier proteins to transport through membrane
specific - only recognised molecules
flows with conc gradient
what is active transport
requires energy ATP
goes against conc gradient
what is pinocytosis
form of endocytosis
molecules bought into cell when part of cell membrane encloses around them and makes then move from outside to inside of cell
molecules may be released into cell or remain in vesicle
What is distribution?
once drug has reaches bloodstream it circulates around the body - and will move into tissues of the body and site of action
quantify distribution
apparent volume of distribution linked to conc present in plasma
water of body can be distributed into four parts in the body . what are they and how much does each represent
Refer to notes
Briefly explain the effect of solubility on a drug
if a drug is lipid soluble it will be able to pass through the cell membrane easily and reach all fluid compartments and have widespread distribution
if a drug is water soluble it will be difficult to cross the cell membrane , it will stay in the plasma and interstitial fluid and continue circulating leaving itself open to be metabolised by the liver and eliminated without reaching tissue
Give an example of plasma protein and give an example of a drug which binds to a protein
Albumin
- warfarin 97% binds to protein leaving only 3% to be active , metabolised and excreted
what drugs will bind to the protein albumin
- bind likely to acidic drugs
if that becomes saturated - lipoprotein - basic drugs - alpha 1 acid glycoprotein
what is volume of distribution
theoretical volume required to contain the total amount of administered drug at the same conc as the plasma
Vd = total amount of drug in body/ drug blood plasma conc
importance of blood flow
heart liver kidney and brain - seconds to mins
muscles , skin , fat
mins - hours
bones
- days - weeks
