Pharmacokinetics (Chapter 2) Flashcards
what are the four effects of the body on the drug that pharmacokinetics study ?
absorption, distribution, metabolism, excretion
what is the definition of the study of pharmacokinetics
study of the effects of the body on the drug
what are the two routes by which drugs are administered and absorbed ?
enteral and parenteral
what is enteral absorption ?
any drug absorbed through the GI tract
what are 4 examples of enteral routes
oral
sublingual
buccal
rectal
what is parenteral absorption ?
any route other than intestine
what are 4 examples of parenteral routes
inhalation
injections
skin rubbing (topical)
skin crossing (transdermal)
what are the pros of the oral route ?
most common because it is easier for adherence.
where is the drug absorbed if it’s ingested orally ?
the small intestine
what are the cons of the oral route ?
drug needs to have special qualities to pass the GI membrane to get into the blood- this means that a protein-based drug like insulin is better injected because otherwise the stomach will digest it.
what is bioavailability ?
the portion of the drug that reaches the systemic circulation and thus has the ability to produce a biological effect.
what is the first pass effect ?
phenomenon of drug metabolism whereby the concentration of a drug is greatly reduced before it reaches the systemic circulation.
after taking the drug it is absorbed by stomach and intestines and transported through the liver via the portal vein. The liver destroys/ excretes part of the drug so only a proportion of the drug makes it to the blood circulation.
explain the elements that influence person-to-person variability of bioavailability of oral administered drugs.
- the simple fact that the amount and rate may vary
- food consumption
- visceral blood flow
- stomach acidity
- stomach emptying
what are the considerations for an athlete when it comes to consuming drugs ?
in competition or in training they have less visceral blood flow, therefore they will have a slower release of oral route drugs
what is the pathway for a drug ingested sublingually or buccally ?
oral mucosa of mouth - veins draining into superior vena cava- heart.
how can one avoid the first pass effect ? what are the implications ?
by not ingesting orally and instead ingesting sublingually or buccally. drugs ingested this way bypass the liver. a lower dosage is therefore recommended because it’s not degraded to the same extent.
when is a drug consumed rectally ? what are its pros and cons
it’s convenient for vomiting or unconscious patient, usually used for a local effect (hemorroids).
however, absorbed poorly, and causes irritation.
what are the advantages of parenteral absorption ?
direct delivery (bypasses GI tract and usually liver), therefore quantity more predictable in blood or tissue.
what are the advantages and limitations of inhaling a drug ?
avantages: large alveolar surface area to cross membrane into pulmonary circulation, meaning there is a rapid entry into the blood stream.
limitations: drug mustn’t irritate alveoles. also, people don’t always do it properly.
give an example of a drug that is better inhaled than injected.
b2-agonist: amphetamine-like symptoms if injected. better inhaled.
what are the 5 types of injections ?
intravenous intra-arterial sub-cutaneous intramuscular intrathecal
what is intravenous injection ? give pros and cons
pro: allows known amount of drug into circulation in a known amount of time, almost instantaneous.
cons: unexpected side effects are difficult to deal with because they occur rapidly
when are intra-arterial injections most commonly used ?
trying to get medication into a specific organ, administering anti-cancer drug to a tumor, and radiolabelled dyes for diagnostic.
when is a sub-cutaneous injection advantageous?
when local response is desired (if problem is in the skin). slower, more prolonged release (like insulin or immunizations, birth control)
when is intramuscular injection advantageous ? what are its cons ?
for local rapid effects that avoid increase in plasma levels. eg epinephrine shot.
cons: pain and soreness
when is intrathecal injection advantageous? where is it done ?
it’s done in the subarachnoid space (CSF), tendon sheath or bursa.
done in pregnancy, surgery, epidural.
is nasal spray enteral or parenteral?
parenteral
is topical good or bad at being absorbed into systemic circulation? what is it used for ?
bad at being absorbed therefore used for more local problems, eg in nasal mucosa or ocular membranes.
how is transdermal different from topical ? what is special about its ingredients ?
transdermal is designed to be absorbed by skin. must be permeable across dermis and resistant to enzymes in dermis? therefore better if drug is mixed in an oily base to make it more lipophilic.
what is an example of a transdermal drug ?
nicotine patches- allows for controlled release into plasma for stable levels.
if a drug is lipophilic, how does it cross a membrane ?
easily. enters the cell and finds its receptor or target
if a drug is hydrophilic, how does it cross a membrane ?
needs a protein receptor or a transporter to bring it into the cell
which tissues get more of a drug ?
the ones with more circulation
is a drug that binds strongly to plasma proteins less or more distributed ?
less
what is the primary site for biotransformation in the body ?
liver
what is an enzyme ?
a protein that causes other chemicals to change
what is a substrate ?
a chemical that is changed by an enzyme
what is a metabolite ?
by-product or produce of the enzyme-substrate interactions
in the liver what is the effect of an enzyme on its substrate, the drug ?
to make the drug less active, therefore more polar / water soluble to be able to send it to the kidney.
what is special about codeine metabolism ?
it is a pro-drug: it becomes more active after metabolism by turning into morphine in the liver
what is a pro-drug?
one that is more active after metabolism; it’s pro-form gets processed into active form.
what are cytochrome p450 enzymes ?
50 types in liver.
how does prolonged use of drug change levels of CYP enzymes?
higher levels because body tries to get rid of drug. to increase enzymes more have to be produced and less broken down.
how does excretion of the drug depend on the structure of the drug ?
if polar- excreted out of kidney.
if lipid-soluble: easily reabsorbed by the distal convoluted tubules and don’t excrete well- have to be metabolized into a more polar form.
what are the 5 ways drugs are excreted
urine, lungs (if drug metabolites that are gaseous), and gall bladder (through bile), sweat, breast milk
what is enterohepatic recycling ?
the drug can be excreted through the gall bladder through the bile, and from there the drug may enter the feces, or be reabsorbed into the blood and be effective again, exceeding the duration of the therapeutic effect of drug.
what injury causes an increased GI tract absorption ?
spinal cord
what injury causes a decreased GI tract absorption ?
burn injury
what drug can increase BP when taken with cheese ?
monoamine oxidase inhibitor
