Drug administration Flashcards
Bioavailability
Bioavailability = proportion of an ingested drug available for clinical effect
Routes of drug absorption
oral
iv
im
transdermal
sc
first pass metabolism
- All blood from GI tract drains through hepatic portal vein and liver before entering systemic circulation,
- Can inactive or activate proportion of the drug
which routes bypass first pass metabolism
- Sublingual route and rectal route
how Distribution of drugs in the body
- Dissolved in blood
- Transported bound to carriers eg. albumin
plasma protein carriers
how does plasma albumin levels affect bioavailibilty
When a drug is administered orally or intravenously, it may bind to albumin in the blood. The extent of binding depends on the drug’s affinity for albumin. Drugs that strongly bind to albumin have a lower fraction of free, unbound drug available to exert their effects, which can reduce their bioavailability.
High plasma albumin = more bound drug = inactive = less action
drug distribution is not even, two compartment model
high blood flow organs and poorly perfused organs/tissues
what is bioavailability affected by?
dosage
route of administration
destruction in gut
poor absorption
first pass metabolism
oral route adv and disadv
o Adv=easy to self-administer
o Disadv=slow onset, variable absorption due to GI tract diseases lowering SA, gastric acids destroy, first pass metabolism
Intravenous and Intramuscular adv and disadv
o Adv=rapid onset, localised, predictable plasma levels, no first pass metabolism
o Disadv= allergic reactions severe, short duration of action, difficult to self inject, higher costs
transdermal and subcutaneous adv and disadv
o Adv=no first pass metabolism, prolonged action due to low blood flow, localised allergic reactions, self medication easy
o Disadv=very slow onset, effects vary from site to site and person to person due to rate of blood flow and fat thickness in subcutaneous tissues
