Drug Movement In Body Flashcards
(34 cards)
What is the dist stage
Process drug leaves the site of admin, enters the blood and subsequently the tissues perfused by the blood
Once within a tissue further blood indept dist, dictated by a conc grad may occur by diff
What is the metab of drug
Process which tissue enzymes principally in liver catalyse chem conv of a freuquently lipid sol drug to often less active and more polar form that is readily excreted
What’s the excretion part
Process remove the drug or its metabolites form the body
What are the steps of drug disposition
Abs
Dist
Metab
Excretion
What are some physicochemical factors controlling drug abs
Solubility - drug must dissolve in order to be abs
Chem stability - destroyed in stomach acid or enzymes in GI tract
Lipid to water coeff - abs usually by simple diffusion across mem
Degree of ionisation - only unionised forms readily diffuse across lipid bilayer unaided
What does the degree of ionisation depend on
PKa of drug and local pH
PKa = pH which drug half ionised and unionised
Use Henderson hasselbach eqn
What is the Henderson hasselbach eqn
For acid - pH - pKa = log(a/ah)
Same for base
As pH increases for an acid the percentage of drug which is ionised is decreased
What is abs of weak acids facilitated by
By the acidic pH of stomach lumen
Bases not abs In stomach but in small intestine
Acidic drugs become less ionised when
In an avid enviro such as stomach whilst basic drugs become less ionised in basic enviro
What are some factors affecting GI abs
GI motility - empty and move thro intestines, mod by drugs and food
PH at abs site
Blood flow to dormancy and int which is increased by food
Way Drug manufactured to release at so rates/sites
Physicochemical interactions
Presence of transporters in mem of epi cells ehci can facilitate Drug abs
What is oral availability
Fraction of drug that reaches the systemic circ after oral ingestion
What is systemic availability
Fraction that reaches systemic Circulation after abs admin via IV
What can happen to orally admin drugs
Become inactivated by enzymes in gut wall and liver before each systemic circ and body tissues
What are some common routes of drug admin
Oral Inhalation Recital IV Subcutaneous Buccal Intramuscular Topical
What are the ads and disads for oral admin
Ads
- simple
- convenient
- non sterile
- good abs for most drugs
Disads
- inactivatin by enzymes or acids
- food binding
- first pass metab
- swallowing
What are the ads and disads for sublingual/ buccal admin
Ads
- rapid abs
- by pass portal system
- avoids gastric acid
Disads
- infrequnet route
- few available
What are the ads and disads of rectal admin
Ads
- rapid abs
- used for nocturnal use
- when oral route compromised
Disads
- infrequent
- vary abs
- aesthetically distasteful
What is an enteral drug
Admin via GI tract
Oral
Sublingual/ buccal
Rectal
What are the ads and disads of IV admin
Ads
- rapid onset
- continuous infusion
Disads
- steril prep
- risk of sepsis or embolism
- high drug levels at heart
What are the ads and disads for intramuscular admin
Ads
- rapid onset for lipid sol drugs
- slow prolonged release
Disads
- painful
- tissue damage
- abs vary
- dept on muscle blood flow
What are the ads and disads of subcutaneous admin
Ads
- ideal for drugs reuniting parenteral admin (peptides)
Disads
- few disads
What are the ads and disads of inhalation admin
Ads
- lungs large sa
- good for volatile agents
- ideal for local effect
Disads
- requires degree of manual dexterity
What are the ads and disads of transdermal admin
Ads
- slow abs across skin to circ can prod a smooth plasma conc
Disads
- suitable for few drugs
- local irritation possible
What are the ads and disads of topical admin
Ads
- ideals for local effect
Disads
- few disads
