quiz 1: module 1 PHARM Flashcards
pharmakon=
drug/poison
kinesis=
motion
pharmacokinetics=
the study of drug movement throughout the body and what happens to this drug on its journey
what are the four basic pharmacokinetic processes
- absorption
- distribution
- metabolism/ biotransformation
- excretion
what is absorption
the movement of a drug from its site of administration into the blood
what is distrubtion
drug movement from the blood to the interstitial space of tissues and from there into cells
what is metabolism
enzymatically mediated alteration of drug structure
what is excretion
the movement of drugs and metabolites out of the body
the 4 processes determine..
the concentration of a drug at its site of action
by knowing pharmacokinetics we can..
maximize beneficial effects and minimize harm
intensity of the response to a drug is directly related to the?
concentration of the drug at its site of action
to maximize beneficial effects, a drug must?
achieve concentrations that are high enough to elicit desired responses, to minimize harm must avoid conc that is too high
balance is achieved by?
selecting the most appropriate route, dosage, and schedule
all four phases of pharmacokinetics involve drug movement, and thus..
membrane crossing
drugs must cross membranes to enter the blood from their site or once in the blood they must..
cross the membrane to leave the vascular system and reach their site of action and must cross membranes to undergo metabolism and excretion
describe the membrane structure
composed of layers of individual cells
- cells so close together that drugs usually pass through the cells rather than going between them
- therefore, ability of drugs to cross a membrane is determined primarily by its ability to pass through single cells
what is the major barrier of crossing a cell?
its cytoplasmic membrane- contains double layer of molecules (phospholipids, have round head and two tails w/ proteins embedded in the layer)
three ways to cross a cell membrane?
- passage through channel or pores
- passage with aid of a transport system
- direct penetration of the membrane itself (not common)
channels and pores?
very few drugs use this way bc channels are very small, specific for certain molecules
-for example sodium and potassium
transport systems?
carriers that move drugs from one side of membrane to another, some require energy
all transport systems are selective based on structure!
-orally would not be able to be absorbed without transport systems
-p glycoprotein is the multidrug transporter protein
p-glycoprotein ? (PGP)
- in liver it transports drugs into bile for elimination
- in kidneys it pumps drugs into urine for excretion
- in placenta it pumps drugs back into maternal blood
- in intense it transports drugs into intestinal lumen
- in the brain capillaries it pumps drugs into the blood
direct penetration of the membrane?
- most drugs the movement is dependent on ability to penetrate membranes directly because
- most drugs are too large to pass through channels or pore
- most drugs lack transport systems
- to directly penetrate must be lipid soluble because membranes are mostly lipids
- polar molecules and ions can not penetrate membranes
what are quaternary ammonium compounds?
contain at least one atom of nitrogen and carry a positive charge at all times
- constant chare is because of atypical bonding to the nitrogen
- unable to cross most membranes, so these compounds must be injected cuz cant get out of lumen of intestine
what is meant by pH dependent ionization?
most drugs are either weak organic bases or weak organic acids and exist in charged and uncharged forms
- whether or not they carry a charge is determined by the pH of the surrounding medium
- acids give up a proton, bases accept protons
- when acid gives up, it becomes nagatively charged
- when base accepts a proton it becomes positively charged
- acids tend to ionize in basic
- basics tend to ionize in acidic
what is meant by ion trapping (pH partitioning)?
because the ionization of drugs is pH dependent, when the pH of the fluid on one side of a membrane differs from the pH of the fluid on the other side, drug molecules will tend to accumulate on the side where the pH favours their ionization
- acidic drugs will accumulate on the alkaline side where there is a pH gradient between 2 sides of a membrane
- basic drugs will accumulate on the acidic side where there is a pH gradient between two sides of a membrane
the rate of absorption determines..
how soon the effects will begin
amount of absorption determines how..
intense effects will be
drug absorption rate is affected by?
the physical and chemical properties of the drug itself and by physiologic and anatomic factors at the absorption site
factor that affect drug absorption?
- rate of dissolution
- surface area
- blood flow
- lipid solubility
- pH partitioning
rate of dissolution & drug absorption
before a drug can be absorbed it must first be dissolved. some drugs allow faster dissolution and have faster onset
surface area & drug absorption
larger the surface area, faster the absorption
blood flow & drug absorption
drugs are absorbed the most rapidly where there is a lot of blood flow because blood containing newly absorbed drugs will be rapidly replaced by drug-free blood, thereby maintaining the concentration between the drug on the outside of blood and inside
lipid solubility & drug absorption
high lipid-soluble drugs are absorbed more rapidly than drugs whose lipids solubility is low because they can readily cross the membranes that separate them from blood
pH partitioning & drug absorption
absorption will be enhanced when the difference between the pH of plasma and the pH at the site of administration is such that drug molecules will have a greater tendency to be ionized in the plasma
two major groups of commonly used routes of administration
enteral (via GI tract)
parenteral (outside GI, but actually means by injection)- intravenous, subcutaneous, intramuscular
the route by which a drug is administered will significantly..
affect both the onset and intensity
barriers to absorption for intravenous?
none because IV puts a drug directly into bloodstream
advantages of IV
rapid onset (emergencies)
- nurse has percise control over levels of drugs in the blood
- permits use of large fluid volumes
- permits use of irritant drugs
disadvantages of an IV
high cost, difficulty, and inconvenience
- irreversibility, no turning back once administered
- fluid overload
- infection can occur from improper technique
- embolism (blood vessel blockage at site distant from point of administration)
intramuscular- barriers to absorption
-only barrier is the capillary wall, in the capillaries that serve muscles, there are large spaces between the cells that make it so drugs can pass through these spaces with ease and need not cross cell membranes, no significant barrier
absorption pattern of intramuscular
may be absorbed rapidly or slowly depending on:
- water solubility of the drug
- blood flow to the site of the injection
advantages to intramuscular
- can be used for administration of poorly soluble drugs (little harm will come from depositing a suspension of undissolved drug in interstitial space of muscle tissue)
- can be used for depot preparations (drug is absorbed slowly over an extended time)
disadvantages of IM
discomfort and inconvenience (pain, can cause local tissue injury)
-IM cannot be used for patients on anticoagulants
subcutaneous..?
very similar to IM, not significant barriers to absorption
- blood flow and circulation are major determinants of how fast absorption takes place
- similar advantages and disadvantages as iM
oral- barriers to absorption
- may be absorbed in stomach, intestine, or both
- 2 barriers: layer of epithelial cells that line the GI tract and the capillary wall
- drugs must pass through the cells rather than between them in the GI tract
- some drugs cause intestinal absorption to be reduced
absorption pattern of oral drugs
rate can be highly variable bc of factors:
- solubility and stability of drug
- gastric and intestinal pH
- food in the gut
- co-administration with other drugs
- special coatings on the drug prep