drug administration Flashcards
what are the stages drugs go through in the body?
administration absorption transport clinical effect metabolism excretion
what are the advantages of oral drug administration?
socially acceptable
drug formulation can change onset and duration of action
what are the disadvantages of oral drug administration?
slow onset variable absorption -food interactions in GIT -GI disease -gastric acid may destroy drug first-pass metabolism
what is first pass metabolism?
all blood from GIT drains to hepatic portal vein
-except sublingual and rectal veins
hepatic portal vein drains to LIVER
-liver metabolises contents
-drug only reaches systemic circulation after passing through the liver once
can inactivate or activate a proportion of the drug
-varies with liver disease & age
give an example of a drug that the liver metabolism inactivates
glyceryl trinitrate (GTN) more needed by oral route to get desired clinical effect
give an example of a drug that the liver metabolism activates
valaciclovir aciclovir
makes an active form of an inactive drug
less needed by oral route
what are the advantages of IV/IM administration?
very rapid onset
predictable plasma levels
no 1st pass metabolism
what are the disadvantages of IV/IM administration?
allergic reactions more severe
short duration of action
access difficulties/self-medication
drug cost higher
what are the advantages of transdermal & subcutaneous administration?
no 1st pass metabolism
allergic reactions localised
prolonged action
-can be days with transdermal patches
what are the disadvantages of transdermal & subcutaneous administration?
very slow onset
self-medication possible
drug cost higher
effect will vary from person to person and site to site
what is bioavailability?
proportion of an ingested drug that is available for clinical effect
what is bioavailability modified by?
dosage form route of administration destruction in the gut poor absorption first pass metabolism
how are drugs distributed?
drug is dissolved in the blood and transported bound to carriers
-usually plasma protein albumin
what can happen when drugs bind to plasma proteins?
bound drug is inactive so can act as a reservoir
drug interactions possible by competitive binding
-warfarin & aspirin
what does the speed of diffusion into tissues from the blood depend on?
the blood flow to the area
the blood wall vessel barrier
active secretion of the drug into the tissue
