Alan Flashcards
What is Pharmacodynamics?
What the drug does to the body.
The relationship between exposure to the drug and effect.
Concentration-response
What is Route?
The site through which the drug is administered
What is Enteral?
Administered via the GI tract; the drug becomes systemically available
What does systemically available mean?
It gets into the patients circulation and is disrupted around the body
What is Paternal?
Administration via a non-GI route that allows delivery into the systemic circulation
What is Topical?
Local administration; the drug does not enter the circulation.
The drug is administered directly to the site of action.
Summary of topical administration?
Limited systemic exposure meaning the drug is not going to result in large concentrations appearing in the patient’s plasma.
Why does topical result in a limited systemic exposure?
This could be because the drug is not absorbed from the site of administration or because a small dose is used.
Why are small doses used in topical administration?
because the drug is being administered directly to the site of action. Meaning you don’t need to give a large dose, to achieve a large concentration at the site of action.
Small dose distributed around the patient’s body = small concentration in the patient so the exposure to be quite small.
What is Percutaneous administration
Administration through the skin
What is subcutaneous administration?
Into the tissue, just beneath the skin layer. An example of parental administration.
What is intramuscular administration?
All the way through the skin, into the muscle tissue. An example of parental administration.
What is intravenous administration?
Into the veins. An example of parental administration
What is transdermal drug delivery?
this is when the drug diffuses through distinct layers of the skin, into systemic or blood circulation to provoke therapeutic effect.
Epicutaneous administration?
Applied on the surface of the skin
Advantages of topical administration?
Fast, local, avoids systmic side effects
What must you consider with Enteral administration?
The drug must survive the gastric acid, and must therefore be able to withstand the pH of the acid, in order to be absorbed from the small intestine.
Absorption is relatively slow (fastest with an empty stomach)
The drug must be sufficiently lipophilic or taken up by a transporter
What is First Pass?
Drug passes through the liver before entering systemic circulation.
Explain the route for first pass?
The drug is absorbed from the small intestine, enters the portal vein, then goes through the liver. It exits the liver by the hepatic vein, into the vena cava and around the systemic circulation.
Why is first pass undesired?
The liver is a site of most drug metabolism.
It prevents the absorption of the drug, from the small intestine into the systemic circulation because most of the drug is getting metabolised in the liver.
Systemic circulation therefore has no opportunity to distribute the drug to other tissues.
First pass reduces bioavailability (the fraction of the drug that gets from the small intestine to the systemic circulation.)
Disadvantages of first pass?
Reduces bioavailability
It might be drug specific
Saturable
Might be affected by liver disease.
What happens if the liver is diseased, concerning first pass?
The rate of metabolism is reduced causing first pass metabolism to also be reduced.
So more drug will enter the systemic circulation.
But more drug in the circulation could lead to adverse effects
What is Enterohepatic recycling?
When the drug passes through the small intestine and to the liver, some of the drug might get excreted into the bile duct and then excreted back into the small intestine, instead of going to the systemic circulation.
This allows the drug to be recycled.
So the exposure of the drug is prolonged
What is Enterohepatic?
Recirculation between the intestine and the liver.
Summary of sublingual admin?
Under the tongue, absorbed through mucosal membranes
Has no first pass effect so it enters the systemic circulation before reaching the liver.
Example of Enteral admin
Summary of Buccal admin?
Absorbed though mucosal membrane of cheek
No first pass effect.
Example of Enteral admin
Summary of Rectal admin?
Through the rectal.
Usually used if the patient is vomiting, unconscious or if the taste of the drug is unacceptable.
No first pass effect.
Absorbed into internal pudendal veins to inferior vena cava
Example of Enteral admin
What can drugs sometimes bind to when in the plasma and why is this bad?
Can bind to serum proteins. These are proteins in the plasma, that can limit distribution into the tissues
What is ADME?
A - Absorption
D - Distribution
M - Metabolism
E - Excretion
Explain A in ADME?
The drug being absorbed from its site of administration into the systemic circulation.
If it is not absorbed into the systemic circulation, it is not considered absorbed.
Explain D in ADME?
once inside the systemic circulation, it can get distributed to different tissues
Explain M in ADME?
This is the chemical transformation of drugs.
They may be converted into metabolites, that have either lost their pharmacological activity (PA), retained their PA, or have gained a new PA
Explain E in ADME?
Excretion via the kideny
Explain elimination?
Happens by metabolism and excretion
It removes the pharmacological active version of the drug.
Explain Disposition?
This is what happens to the drug after entering the systemic system (after being absorbed) – distribution and elimination
What is whole blood?
uncoagulated and containing red and white blood cells
What is Plasma?
uncoagulated blood, devoid of cells
What is serum?
coagulated blood, devoid of cells
What does devoid of cells?
the red and white blood cells have been removed
Meaning of coagulated?
changed from a fluid form to a solid form
Explain intravenous admin in terms of graph?
On the graph, the concentration decreases over time (in the plasma), quite quickly. The drug is instantaneously available.
Explain Oral admin, in terms of graph?
At the start of the graph, absorption is occurring more than distribution and elimination
The concentration increases in the plasma and reaches a maximum conc value called Cmax (this is the maximum concentration achieved). The concentration then starts to decrease.
Towards the end of the graph, when it is slopping down, elimination is occurring more than absorption and distribution.
Explain Cmax?
the rate of which it is being absorbed = the rate at which it is being eliminated.
Why is the maximum concentration for oral generally lower than intraveous?
Because in its early phase, when the drug is being absorbed, some is also being eliminated. So when you administer a drug orally, there’s never a point when all the drug is in the body.
Whereas there is a point where all the drug is in the body, with intravenous admin
What is Tmax?
The time at which the maximum concentration is achieved.
