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Med Chem Midterm > Lecture 2 -Lecture 3 > Flashcards

Lecture 2 -Lecture 3 Flashcards

1
Q

most drugs pass through biological membranes according to what?

A

their partition coefficients

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2
Q

what does “foreign organics” mean

A

explains most drug molecules

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3
Q

the higher the partition coefficient……

A

the higher the lipophilicity, and thus the easier it is to cross the membranes

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4
Q

how do you calculate the partition coefficient of a drug?

A

PC = solubility in organic phase/solubility in aqueous phase

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5
Q

can anything other than lipophilic substances diffuse through the biological membrane?

A

YES – there is a specialized situation in which water, ions, and low MW polar compounds can diffuse through AQUEOUS CHANNELS in the membrane

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6
Q

the biological membranes are highly _____

A

lipophilic

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7
Q

true or false

more lipophilic = worse absorption

A

FALSE – better absorption (more drug goes into cell)

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8
Q

compare the relative partition coefficients of phenobarbital, secobarbital, barbital, and pentobarbital

what does this mean about their % absorption?

A

HIGHEST PC = secobarbital
pentobarbital
phenobarbital
LOWEST PC = barbital

this means that secobarbital has the highest % absorbed (50%) and barbital has the lowest % absorbed (10%)

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9
Q

true or false

the higher the partition coefficient of a drug, the higher the % absorbed

A

TRUE

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10
Q

In general, as the PC increases, % drug absorbed also increases.
HOWEVER……

A

the lipophilicity of the drug should be OPTIMUM (not too high, not too low)

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11
Q

give 3 things that can happen if a drug is too lipophilic

A

-it may become INSOLUBLE in biological fluids and start clumping

-it may be lost to neutral fats

-it may undergo rapid metabolism

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12
Q

give 2 things that can happen if a drug is too hydrophilic

A

-it cannot pass through biological membranes readily

-it is excreted rapidly

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13
Q

modifying a drug to increase lipophilicity is favorable but…..

A

only up to a certain extent (don’t want too lipophilic bc the drug may become insoluble in body fluids and start clumping, be lost to neutral fats, or undergo rapid metabolism)

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14
Q

is the target of a drug usually extracellular or intracellular

A

intra

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15
Q

most drugs are….

A

weak acids or weak bases

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16
Q

“degree of ionization” can be represented by…

A

pka

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17
Q

most drugs are weak acids or weak bases and their ____ and _____ of the environment influence their LIPID/WATER SOLUBILITIES

A

most drugs are weak acids or bases and their PKA (degree of ionization) and PH OF THE ENVIRONMENT influence their lipid/water solubilities

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18
Q

true or false

passing in/out of biological membranes is important for drug delivery

A

TRUE

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19
Q

unionized molecules possess higher _____ (water or lipid?) solubility

A

lipid

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20
Q

unionized molecules pass most membrane barriers _____(more or less readily) than ionized molecules.

A

MORE READILY

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21
Q

give 2 reasons why unionized molecules pass most membrane barriers more readily than ionized molecules

A
  1. the lipoprotein that forms the cell membrane is highly charged. therefore, ionized molecules will either be REPELLED or BOUND TIGHTLY (depending on opposite or like charges) which decreases membrane penetration
  2. ionized molecules get hydrated and thus increase in size – larger in size than their corresponding unionized species which makes it harder to cross the membrane
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22
Q

explain the Bronsted-Lowry theory of acids and bases
(include: what an acid and a base are, what happens when they undergo a reaction)

A

an acid is any substance capable of yielding a proton

a base is any substance capable of accepting a proton

when an acid gives up a proton to a base, it is converted to its conjugate base

when a base accepts a proton from an acid, it is converted to its conjugate acid form

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23
Q

give the formula of methylamine.
is it an acid or base?

A

CH3NH2
base.
when it accepts a proton, it becomes CH3NH3+ (methylammonium)

24
Q

what is the ionized form of acetic acid

A

CH3COO- (acetate)

25
Q

give the Henderson-Hasselbalch equation

A

pH = pka + log [A-]/[HA]

26
Q

give the variation of the Henderson-Hasselbalch equation that can be used to calculate the pka of weak acids and bases

A

pka=pH + log [protonated form]/[unprotonated form]

protonated form = HA
unprotonated form = A-

27
Q

“protonated form” does this mean it’s ionized or unionized?

A

it depends on if the substance is a base or an acid

when bases are protonated, they’re converted to their ionized form (BH+)

When acids are protonated, they’re converted to their unionized form (HA)

28
Q

what does %I mean

A

% ionized

29
Q

when pH = pka, what can you say about % ionization?

A

% ionized = % unionized
50%-50%

30
Q

when pH <pka, what can you say about % ionization?
what area in the body mimics these conditions?

A

when pH<pka, protonated forms predominate
stomach has these conditions

31
Q

the pka for acidic drugs is usually around what value?

A

3

32
Q

in an acidic environment, will basic drugs be ionized or unionized?
what does this mean?

A

ionized – therefore, basic drugs are not well absorbed in the stomach

33
Q

when pH>pka, do protonated or deprotonated forms predominate?
what area of the body has these conditions?

A

deprotonated forms predominate
these are the conditions of the small intestine

34
Q

in the small intestine, which are more likely to be absorbed better – weakly acidic or weakly basic drugs as compared to the stomach?

A

the small intestine has a higher pH in the stomach.
deprotonated forms predominate.
weakly basic drugs will be unionized and are thus better absorbed

35
Q

give a representation by using letters of a protonated acid and an unprotonated acid, as well as a protonated base and an unprotonated base

A

protonated acid – HA
deprotonated acid – A-

deprotonated base – B
protonated base – BH+

36
Q

in terms of letters, what is the unionized form of an Acid, and what is the unionized form of a base

A

unionized acid = HA
unionized base = B

37
Q

the distribution of a drug between the ionized and unionized form depends on…

A

the pH of the medium and the pka of the drug

38
Q

ka=…

A

concentration of products/concentration of reactants

39
Q

true or false

most drug molecules reach the site of action

A

FALSE

40
Q

most drug molecules do NOT survive to reach the site of action.

why?

A

they can undergo 4 different things that prevent reaching the site of action

-protein binding
-binding to neutral fats
-drug metabolism
-excretion

41
Q

name 4 sites of loss for drugs before they reach the site of action.
explain them too

A

-protein binding – many drugs are highly protein bound and will bind to a serum protein like albumin. they must be free in order to reach the site of action

-binding to neutral fats – especially if the drug is very lipophilic

-drug metabolism – especially the case for oral drugs. 1st pass effects (liver) destroys most of the drug (especially if very lipophilic)

-excretion – water soluble drugs go straight out in urine and dont need to be metabolized

42
Q

drug metabolism is a site of loss for drugs.
for which drugs is this most relevant?

A

oral drugs because of 1st pass effects

43
Q

for which drugs is excretion the biggest concern as a site of loss?

A

very water soluble drugs – go straight into urine and aren’t even metabolized

44
Q

most and almost all drugs bind to albumin in the blood plasma in a _____ fashion

A

REVERSIBLE
the drug can unbind if free drug clears (through excretion/metabolism/reaches site of action) to maintain equilibrium

45
Q

true or false

protein binding to albumin is NOT unidirectional

A

true - it can unbind

46
Q

drug-protein binding is due to what force(s)?

A

ionic and/or nonionic bonding

47
Q

is drug-protein binding selective or nonselective?

A

nonselective

48
Q

when a drug undergoes protein binding, it cannot cross the membranes, and is said to be _____

A

INACTIVE

49
Q

Can a drug that is bound to protein be metabolized or excreted?
explain

A

NO.
therefore, protein binding can be used to our advantage to prolong the duration of the drug’s activity

50
Q

give an example of a drug that uses its protein binding affinity to prolong the duration of action

A

trypanocide suramen

this is an anti-parasite that binds to the protein (can’t be metabolized when bound)and slowly releases in order to increase the duration of action. bound drug serves as a depot - slow release, and long duration of action

51
Q

what is the clinical significance of drug-protein binding?

A

bound drugs and endogenous substances (substances within the body) can be displaced by other drugs, leading to DRUG INTERACTIONS

52
Q

Give 2 examples of drug interactions related to drug-protein binding

A

warfarin (anticoagulant) is displaced from its albumin-binding sites by several drugs such as phenylbutazone, clofibrate, and sulfonamides

bilirubin (breakdown byproduct of blood cells) is protein bound and can be displaced by sulfonamides and other organic anions. issue for fetus and newborn

53
Q

why is the protein-binding interaction of warfarin a significant concern?

A

warfarin has a narrow therapeutic index, meaning anything that alters its blood concentration can be dangerous.

many drugs (ie phenylbutazone, clofibrate, and sulfonamides) have albumin binding sites so this is a big clinical concern. the binding is not very specific in the case of albumin

54
Q

the sulfonamides are ___ ___

A

organic anions

55
Q

organic anions displace what from its protein binding site?
also, give a specific example of a drug that is an organic anion

A

displace bilirubin
sulfonamides

56
Q
A

Med Chem Midterm (11 decks)

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