absorption and distribution. ch 1 pg 15-24 Flashcards
the olive oil partition coefficient is used to express?
the lipid solubility of the drug
put drug into a mixture of half water half oil and see how much of the drug dissolves in each substance
drugs that are more highly lipid soluble will be more concentrated and which substance in the olive oil test?
the olive oil
why is it important to tell how lipid soluble a drug is?
measure the degree to which a drug will dissolve in fat tissue in the body
when a molecule carries an electrical charge (ion) it looses its ability to?
dissolve in lipids (unable to pass through membrane)
3 ways to determine the percentage of ionized molecules in a solution?
1) whether the drug is a weak acid or base
2) whether it is dissolved in an acid or a base
3) its pKa
what is the pKa of a drug?
the pH at which half its molecules are ionized
on the pH scale #s below 7 are? and #s above 7 are?
below= acid
above=base
what is the pH of the lining of the intestine?
3.5
morphine is a ? with a pH of?
base , 8
will morphine be absorbed by the digestive system?
no. because bases are highly ionized in solutions with low pH such as the intestine (3.5). ionized molecules cannot cross the membrane
caffeine is a base that has a pKa of 0.5 what does this say about its absorption in the body?
almost completely nonionized in the digestive system (can be absorbed)
if 97% of a drug is ionized in the digestive system, and only 3 % is lipid soluble, what will happen?
the 3 % will diffuse through the membrane and be removed by the blood and then a new 3% becomes non ionized and diffuses. the process continues until equilibrium is reached.
the percentage of ionization determines the ? of absorption.
rate
transdermal administration?
drug is absorbed through the skin
what is the main layer of skin that is a barrier to absorption?
epidermis (outer layer)
the epidermis is made of flattened cells densely packed with?
keratin?
characteristics of epidermis
impermeable to water
- can only be penetrated by lipid soluble substances
the drug is separated by the skin by a special membrane that controls the rate of absorption
- this is what kind of drug use?
a patch
highly lipid soluble drugs tend to concentrate where?
in body fat outside the CNS
why is it not good when drugs get absorbed by fat?
it keeps them there preventing them from reaching their SOA.
what can the pKa also influence?
why?
where a drug gets to in the body
–> anywhere int he body it can get trapped inside a membrane depending on its pH
drugs that are weak bases tend to ionize in? and drugs that are weak acids tend to ionize?
- acidic solutions
- basic solutions
a difference in pH across the membrane of 1.0 will cause a drug to be ? more concentrated on one side than the other
- and difference of 2.0?
10 x
100x
?is a result of special cells in the central nervous system that wrap themselves around the capillaries and block the pores through which substances normally diffuse
blood brain barrier
what substances have great difficulty getting though the blood brain barrier?
non lipid soluble substances
contains specialized cells that play an important role in detecting impurities or toxins in the blood and elicits vomiting by stimulating the vomiting center in an attempt to rid the body of these substances.
area postrema of the medulla oblonganta
plays an important role in de- tecting hormone levels in the blood, especially those hor- mones involved in regulating the balance of bodily fluids.
subfornical organ in the brain
intermediary organ between the fetus and the wall of the uterus
the placenta
what drugs cross the placenta barrier more easily?
highly lipid soluble
what percentage of the drug that the mother takes reaches the blood of the baby within 5 minutes?
75%-100%
the major job of elimination is done by ? they are known as?
the liver and kidneys
–> the dynamic duo of excretion
what is the function of the liver?
molecules are modified to form new substances useful to the body, and toxic molecules are changed into less harmful substances to be filtered out of the blood by the kidneys
an enzyme is a?
catalyst (a substance that controls a certain chemical reaction)
the body controls chemical reactions by?
controlling the amount of enzyme available to act as a catalyst
alcohol dehydrogenase is an example of?
an enzyme
the process of restructuring molecules is referred to as?
metabolism
the products of metabolism are?
metabolites
the metabolic process where drugs are concerned
detoxification
2 general rules about metabolites
1) MOST of the time they are less toxic then the original substance
2) they are usually more likely to ionize
explain first pass metabolism
Drugs that are absorbed from the digestive system are absorbed into blood that goes to the liver before it returns to the heart
Their primary function is to maintain the correct balance between water and salt in body fluids
-> they also physically remove molecules from the blood
kidneys
the functional part of the kidney is? at one end of this tube structure is called? and inside this is a clump of the capillaries called the ?
nephron, bowmans capsule, glomerulus
what ever is not reabsorbed into the blood passes through the nephron and is?
excreted form the body through urine
what is the ph of blood and urine
blood = 7.5 urine = 6
acids or bases tend to be retained in the urine and excreted more easily?
bases
the rate of excretion can be described in terms of ?
half life
at low conc. the rate of metabolism will be?
lower
time taken for the body to eliminate half of a given blood level of a drug
half life
When the elimination of a drug changes with concentration in this half life manner, it is said to have?
first order kinetics
one drug that does not eliminate in a half life manner
alcohol
rate: 15mg alcohol/ 100mg of blood/ hour
when the rate of elimination of a drug is a straight line (alcohol) is it said to have?
zero order kinetics
in alcohol metabolism, alcohol is converted to? by the enzyme? then the acetaldehyde is converted to ? by another enzyme called?
acetaldehyde, alcohol dehydrogenase, acetyl coenzyme, aldehyde dehydrogenase
enzyme induction is?
Levels of a given enzyme can be increased by previous exposure to a specific drug that uses that enzyme or some other enzyme system.
what contributes to generating a tolerance for a drug
enzyme induction
disulfiram is a drug t blocks? hat
aldehyde dehydrogenase
drinking what juice can increase the blood levels of many drugs?
grapefruit juice
does drug metabolism differ with age?
yes
a time course if referring to?
the effect of the drug changing over time in a single administration
the absorption rate of a drug can change depending on what?
the route of administration
the therapeutic window refers to?
when drugs are taken for therapeutic purposes it is important they stay within the right blood level within your body for the best effects.
–> take the correct dose at the given intervals
lithium carbonate is given to ppl with? and has a very ? therapeutic window
bipolar disorder
- narrow
