Pharmacokinetics Flashcards
Three ways to cross a cell membrane
channels and pores transport systems direct penetration (most common, lipid soluble)
Four basic processes of pharmacokinetics
absorption
distribution
metabolism
excretion
Which of these can cross cell membranes: lipids, polar molecules, ions
just lipids
Movement of drug from its site of administration into the blood
absorption
Factors of absorption
rate of dissolution surface area blood flow lipid solubility pH partitioning
enteral
GI tract
parenteral
Goes straight into the blood stream: intravenous, subcutaneous, intramuscular
Which of these routes are parenteral: subcutaneous, nasogastric tube, transdermal, intravenous
subcutaneous
intravenous
sustained release
formulation change to allow for ongoing release – pts can take less frequently
movement of drugs throughout the body
distribution
components of distribution
blood flow to the tissues
exiting the vascular system
ability of the drug to enter the cell
blood brain barrier
protective mechanism for the brain: tight capillaries make it difficult for drugs to penetrate
Which drugs can pass most easily to a fetus
lipid-soluble and non-ionized
enzymatic alteration of a drug
drug metabolism
where does drug metabolism take place (mostly)
liver
cytochrome p450
12 closely related enzymatic processes that change the drug
Ways CYP can change drug
accelerate excretion
inactivate/activate
↑/↓ toxicity
↑/↓ metabolism (inducers/inhibitors)
First Pass Effect
oral meds go from GI tract to liver, inactivating a portion of the drug
(time delay, different dosage parenteral and enteral)
removal of drugs from the body
excretion
primary organ of drug excretion
kidneys
Drug excretion pathways
lungs, milk, sweat/tears/skin/hair, saliva, bile, urine
three factors affection drug excretion from kidneys
glomerular filtration rate
passive tubular reabsorption
active tubular secretion
lag period
time between drug initiation and onset of effect
therapeutic window
range between desired response and adverse response
why is half-life important? (3)
It’s a major determinant of:
- duration of action after a single dose
- time required to reach steady state
- dosing frequency
t1/2
drug half life
how many half lives does it take for the drug to plateau
4 (the amount of drug eliminated between doses equals the amount ingested)
how many half lives does it take for most of the drug to be eliminated
4
what are loading doses
higher or more frequent dosage at initiation to make plateau faster
peak level
greatest concentration of the drug in the blood (30 minutes after infusion)
trough level
greatest concentration of the drug in the tissue (30 minutes prior to next infusion)
why is trough important
high trough can increase potential for adverse effects – may hold dose
efficacy
the largest effect a drug can produce
potency
dosage needed to produce effect
t/f: selective drugs are safer
false
the more selective a drug is, the [more/fewer] side effects it will produce
fewer
strength of attraction between drug and receptor
affinity
ability to activate receptor upon binding
intrinsic activity
agonist drug
affinity and intrinsic activity: mimics and enhances body response and cellular activity
antagonist drug
affinity without intrinsic activity: binds to receptor and blocks normal body response
