Absorption Flashcards
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Define
Pharmacokinetics
(2)
Study and characterization of drug: ADME, with the aid of mathematical models which allow data to be interpreted.
What is the difference between
pharmacokinetics and Pharmacodyanmics?
(2)
Pharmacokinetics: Effect of body on drug
Pharmacodynamics: Effect of drug on body
Explain
Clinical pharmacokinetics
(1)
The application of pharmacokientics in the safe and effective therepeutic managment of the patient.
Summarise
Pharmacokinetics, Pharmacodynamics, Pharmacotherapeutics
(3)
- Pharmacokientics: ADME
- Pharmacodynamics: drug/receptor interaction
- Pharmacotherapeutics: Drug effect/response
State how we can use
The pharmacokientic properties of a drug
(3)
Dose and frequency of drug
How to change dose in certain medical conditions
How some drug interactions occur
Define
Abosrption
(1)
Movement of drug from site pf administration, across membranes and into the bloodstream
Note the factors
Which affect the rate of absorption
Red doors like working
(4)
- Route of administration
- Dose (concentration)
- Lipid-solubility of the drug
- Weak organic acid/base drugs
Draw a table
with routes of administration and their site of absorption
(10)
Draw table
Most drugs are weak organic acids/bases, what does this tell us?
- Most drugs are hydrocarbon molecules, sucg as aspirin, vitamins.
- They undergo ionisaiton/dissociation
- The pH of the solution as well as the pKa of the drug will tell us if the drug is in an ionised or non-ionised state.
Henderson - Hasselbach equation
(5)
pH = pKa + log (A- / HA)
- pH = -log(H+)
- pKa - dissociation constant for the acid
- A- -concentration of the conjugate base
- HA - concentration of the acid
Define
Passive diffusion
Movement of molecules from a higher concentration to a lower concentration, down a concentration gradient not requiring energy
Requirements of
passive diffusion
- Water solubility - almost all drugs are sufficiently water soluble
- Lipid solubility - some drugs lack the necessary lipid solubility
- In practice, passive diffusion depends mainly on lipid solubility
Draw a table with
Which molecules are effieicnet/ineffieicent in passive diffusion?
5|3
draw a table
Define
facilitated diffusion
(1)
Selective gateway allows entry of one group of molecules, but excludes all others.
What is
active transport
(3)
- Structurally selective
- Requires energy
- Can operate against the concentration gradient
Specifity of modes of transport?
(2)
- Pasive diffusion - non specific, anything lipid soluble
- Faciliated diffusion & Active transport - structurally specific group of molecules
What are
p-glycoproteins?
(4)
Proteins with carbohydrates attached
- found in the apical cell membrane (facing gut contents)
- Substances are absorbed, but then actively pumped back into the gut contents (efflux).
- ATP dependent
Draw a table showing
Location of P-glycoproteins
(4)
draw a table
State the purpose of
P-glycoproteins?
(1)
Gnereally a defense mechanism against foreign substances
What is
p-glycoprotein mediated efflux
(1)
This is when substances are absorbed, but then activley pumped out into gut contents, decreasing their absorption
Examples of substances where intestinal absorption is opposed by p-glycoprotein mediated efflux
(6)
Celiprolol - Beta blocker
Cyclosporin - immunosuppresant
dexamethasone - glucocorticoid
ivermectin - anthelmintic
verapamil antihypersensative
vincristine - cytotoxic
What is
Induction of p-gp
answer with example
(2)
example Rifampicin increase the amount of P-gp in the instestinal epithelium. this reduces absorption of other substances
What is
inhibition of p-gp
answer with example
(2)
example: Large enough doses of verapamil will saturate the p-gp. Other substances then absorbed more easily. Has been suggested as a means to increase absorption of problem molecules
What is
bioavailability (F)
(2)
The fraction of a dose that reaches the systematic circulation in a chemically unaltered form
1. as percentage or decimal
2. has no units
Causes of
Incomplete bioavailability
(4)
- Failure of disintegration or dissolution
- Chemical, enzymatic, or bacterial attack
- Failure of absorption and pGp efflux
- First pass metabolism in the gut wall/liver
Causes of
failure in absorption
(3)
- Binding to other molecules in the gut content
- Too polar to udnergo passive diffusion
- p-gp efflux
Explain the
Ionisation of weak acids
(1)
will ionise more as the pH of the solution increases (the solution becomes less acidic) and vice versa
Explain the
Ionisation of weak bases
(1)
Will ionise less as the pH increases and vice versa
Explain the
effect of ionisation on drug absorption
membranes
(1)
Ionised drugs become too polar to cross the lipophilic layer across membranes
In practice
Acidic drugs absorption
where in the body
(3)
In practice, acidic drugs will be absorbed mostly in the small intestine, this is because the surface fo the small instestine has villi and microvilli which greatly increasse the surface area of absorption.
In practice,
Talk about the absorption of basic drugs and where absorption occurs
(3)
A basic drug will not be absorbed in the stomach all since pH is too low. so all of the drug will be abosrbed in the small intestine where the drug is unionised and the surface area is large.
