IV: barriers to absorption
none (absorption bypassed)
IM: barriers to absorption
capillary wall
sub Q: barriers to absorption
capillary wall
PO: barriers to absorption
epithelial lining of GI tract: capillary wall
disadvantages to IV
- irreversible
- expensive
- inconvenient
- difficult
- risk of: fluid overload, infection, embolism
- drug must be water soluble
disadvantages to IM and subQ
- discomfort
- inconvenient
- potential injury
disadvantages to PO
- variability
- inactivation by gastric acid and digestive enzymes
- possible n+v from local irritation
- patient must be conscious + cooperative
factors affecting absorption
- rate of dissolution
- surface area
- blood flow
- lipid solubility
- pH partitioning
factors affecting distribution
- blood flow to tissue
- ability of drug to enter vascular tissue
- ability of drug to enter cells
define drug distribution
drug movement from the blood to the interstitial space and then into the cells
factors affecting metabolism
- age
- induction & inhibition of drug metabolizing enzymes (increase rate of metabolism, accelerate metabolism of other drugs)
- first-pass effect
- nutritional status (ex. malnourished)
- competition between drugs
3 steps for excretion
- glomerular filtration
- passive reabsorption
- active secretion
factors that affect excretion
- pH dependent ionization
- competition for active tubular transport
- age
minimum effective concentration
a level a drug must be at or above to be effective
toxic concentration
too much drug is in the system
peak concentration
time for the drug to reach it’s maximum response
trough concentration
lowest level of concentration: must be kept above this to have a therapeutic effect
loading dose
a high amount of the drug given once or twice to “prime” the blood stream with a level sufficient to induce a therapeutic response
maintenance dose
dose given before plasma levels drop back towards zero in order to keep the plasma drug levels in a therapeutic range
maximal efficacy
the largest effect a drug can produce
relative potency
the amount of the drug we must give to elicit an effect
agonists
bind and activate receptors - mimic the bodies own endogenous regulatory molecules
antagonists
prevent receptor activation (turns it off)
ex. narcan
ED50
average effective dose - standard dose
dose required to produce a defined response in 50% of the population
