drug administration and absorption Flashcards
what are the main types of targets for drugs
enzymes, transporters, ion channels and receptors
- most often than not they interact with proteins
what is the most common drug target
enzymes
what are receptors
proteins that respond to an endogenous messenger by initiating a signal
what do selective binding sites act as
molecular switches, switching the cell on and off
what are the two types of receptor drugs
agonists and antagonists
how does an agonist receptor drug work
it reproduces the effects of endogenous messengers
how do antagonists drug receptors work
they block the effects of the endogenous messenger
what does the extent to which a drug binds to its
target protein depend on
its local concentration
which 3 targets are predominantly targeted by inhibitors
enzymes, transporters and receptors
what type of drug target is effected by agonists and antagonists
receptors
what does ADME[Tox] stand for
Absorption
Distribution
Metabolism
Excretion
Toxicity
define PHARMACOKINETICS
How body controls drug
concentration at site of action
define PHARMACODYNAMICS
Effect of drug on target
cell / tissue
why is pK important
- Analysis of the behaviour of drugs after administration
- Essential for designing dosing regimen and understanding
variation in responses between patients
-PK parameters can offer insight into the disposition of the
drug after administration
what are the 10 routes of administration
PO, NG, S/L, MR, PR, IV, TOPICAL, OPHTHALMIC, INHALATION , NASAL
that route of administration is PO
enteral (oral)
that route of administration is NG
nasogastric
that route of administration is S/L
sublingual
that route of administration is MR
controlled release
that route of administration is PR
rectal
that route of administration is IV
parenteral
that route of administration is TROPICAL
skin
that route of administration is OPHTHALMIC
eye
that route of administration is INHALATION
lungs
that route of administration is NASAL
nose
concentration an be found by
measuring the drug concentration of the blood plasma as most drugs circulate via the circulatory system
what is a therapeutic window
the therapeutic range where the drug is effective, too much and it becomes toxic too little and its ineffective within the body
why are drugs with a narrow therapeutic range difficult to use
patients will need to be monitored more frequently
what does MTC stand for
maximum tolerated concentration
what does MEC stand for and what does it tell you
minimum efficacious concentration
- tells you the minimum amount of a drug that can be taken for it to still be effective
why does absorption cause a delay
as the drug has the diffuse into the blood plasma before traveling to the target area
what is the half life of a drug
the time taken for the concentration of the drug in the blood to decrease by half
what is the half life of oxazepam
5-10 hours
what is the half life of diazepam
20-80 hours
what is considered when choosing a route of administration
- ease e.g. complient patient
- kinetics of the drug (duration of action)
- local vs systemic effects
define absorption in the administration of drugs
the transfer of a drug from its site of administration to its site of action (PK)
define bioavailability in the administration of drugs
The extent to which a drug can overcome the
barriers to absorption (including first pass
metabolism) and enter the systemic circulation
what 2 mechanisms can dugs travel by to enter the blood stream
passive diffusion and active transport
how does passive diffusion work during drug absorption
diffuses through phospholipid bilayers
- the rate of diffusion depends upon
– the concentration across the membrane
–thickness of the membrane
– the surface area of the absorption surface
A number of factors affect uptake in the GI tract such as….
-Formulation of drug ( Tablet vs. solution, variation in additives between brands)
-Gastrointestinal mobility ( Presence of food or pathology can delay transit time)
-Food constituents ( Ca2+binds tetracyclines making them unavailable for absorption)
-G secretions & gut wall enzymes (Can destroy / inactivate drugs)
what are the advantages using the GI tract as the site of absorption
-Large surface area
- Range of pH environments promote uptake of weak
acids/bases
-Rich blood supply
-Long dwell time
-Some active transport (e.g. Levodopa taken up by
phenylalanine transporter)
-Small intestine is major site for absorption
why are there differences in rates of absorption from different muscle groups
each muscle group will experience different flows of blood to them
The efficiency of absorption can be quantified by what two variables
- Bioavailability (F)
- Time to peak (tmax)
what is Time to peak (tmax)
a measure of the rate of absorption
what is Bioavailability (F) a measure of
a measure of the proportion of dose absorbed (Compared to iv delivery of the same dose)
