Weak Acids and weak Bases

Question 1

to determine if a drug is largely ionized or largely non-ionized you will need to know what 3 things?

Answer 1

• If the drug is a weak acid or weak base (must memorize)
• the pKa of the drug
• the pH of the target solution

Question 2

weak acids become more ________ when pH decreases (acidic) and more _______ when pH increases (basic)

Answer 2

non-ionized

ionized

Question 3

weak bases become more ______ when pH increases (basic) and more _____ when pH decreases (acidic)

Answer 3

non-ionized

ionized

Question 4

the pKa is your reference what is it?

Answer 4

it’s when the pH of a solution is the same os the pKa of the drug the drug will be 50% non-ionized and 50% ionized (equilibrium)

Question 5

why is the pH of the target solution inportant to know

Answer 5

when you know the pH of the solution the weak acid or weak base is being placed in, you use your reference pKa to determine if the weak acid or weak base in the question is more the 50% ionized or less than 50% non-ionized in the solution

Question 6

which is the active part? ionized or non-ionized

Answer 6

non-iionized

Question 7

what are examples of weak acids?

Answer 7

thiopental

Barbiturates

propofol

Question 8

Weak Acids:

what do they do with the H+ ion

Answer 8

weak acids GIVE UP H+ ions (but do not dissociate completely)

Question 9

Weak Acids:

whay are they called Weak Acids

Answer 9

acids give up hydrogen

called weak b/c they don’t dissociate completly

Question 10

Weak Acids:

ex

Answer 10

Hbarb = weak acid; non-ionized; lipid soluble

Barb- = conjugate base; ionized; water soluble (has charge)

Question 11

Weak Acids:

pH = what?

Answer 11

pH = pKa

Question 12

pH of body for all problems unless otherwise stated

Answer 12

7.4

Question 13

Weak Acids:

what happens to weak acids as the pH falls (H+ increases)

Answer 13

become more non-ionized

Question 14

Weak Acids:

Acid + Acid =

Answer 14

nonionized

(acid in an acidic enviroment = non-ionized or more active free drug available)

Question 15

Weak Acids:

the pKa of a Weak Acids is what?

Answer 15

it is the pH at which 50% of the Weak Acid is in the ionized form and 50% of the Weak Acid is in the non-ionized form

Question 16

Weak Acids:

an ex of pKa with Weak Acids is as follows:

the pKa for thiopental is 7.6 so is the pH of the pt was 7.6 there would be 50% ionized and 50% non-ionized. what would happen it the pH was 7.4?

Answer 16

more than 50% would be non-ionized (in this case to be exact 68% would be non-ionized)

Question 17

Weak Acids:

are the pKa’s different for different Weak Acids?

Answer 17

yes one Weak Acid may have a pKa of 2.3 while another may have a pKa of 11.2

a given Weak Acid may have any pKa

the pKa is constant for a given Weak Acid

Question 18

Weak Acids:

The (ionized or nonionized) drug penetrates the BBB and the placental barrier. the more (ionized or non-ionized) the drug the greater transfer to the brain or fetus

Answer 18

Non-ionized

Non-ionized

Question 19

Weak Acids:

strictly speaking the non-ionized form of the Weak Acid is called the ______, and the ionized form is called the _____ ____

Answer 19

acid

conjugate base

Question 20

Weak Acids:

what are the steps in order to solve any Acid base question

Answer 20

1. is drug weak acid or weak base
2. what is the pKa of the drug
3. what is the pH of the target solution

Question 21

Weak Acids:

when drawing a graph if dealing with weak acids non-ionizd over the Acidic portion of the graph

(acid + acid = nonionized) and then ionized over the basic aspect of the graft.

also for all puproses get use to writting less ionized which is the same as more non-ionized and less un-ionized which is the same as more ionized

Answer 21

Question 22

Weak Acids:

assume drug Y is a barb

state if the drug has more ionized or non-ionized

do steps 1, 2 , 3 in order

Answer 22

more NON-ionized

Question 23

Weak Acids:

assume drug Y is a barb

state if the drug has more ionized or non-ionized

do steps 1, 2, 3

Answer 23

More IONIZED

Question 24

Weak Acids:

the greater the pKa of a weak acid the greater amount of the drug in the _________ form at physiologic pH of 7.4

Answer 24

non-ionized

Question 25

Weak Acids: will induction with thiopental be faster is the pt is acidodic or alkolotic? explain.

Answer 25

thiopental (weak acid) induction would be faster if ACIDODIC when a pt is acidodic, more of the injected thiopental will be non-ionized (acid + acid = nonionized) thiopental will diffuse in greater amounts across the BBB b/c more of the drug is in the non-ionied form non-ionizd drug readily penetrates the BBB

Question 26

Weak Acids: should you mix thipoental with a low pH solution? explain

Answer 26

Thiopental = weak acid no when thiopenal is mixed with a solution of low pH (pH 3.0) most of the drug will become non-ionized. Non-ionized drugs, b/c it is poorly water soluble, tends to precipitate. weak acids should not be mixed with a low pH solution bc a precipitate might form RULE: mixing Weak Acids with a low pH solution may lead to form a precipitate

Question 27

Weak Acids: why is thiopenal mixed and stored in a solution with a pH of 10-11

Answer 27

thiopental = Weak Acid most of the drug is in the ionized form ionized drugs are highly water soluble a precipitate will not form when thiopental is stored with a solution witf a high pH

Question 28

Weak Bases: weak bases do what with H+

Answer 28

weak bases accept a H+, but never do so completely

Question 29

Weak Bases: picking up a H+ (proton) means it becomes pronated or \_\_\_-

Answer 29

charged

Question 30

Weak Bases: label what is non-ionized

Answer 30

LA = Lipid soluble, NON-ionized; weak base H+ = base LAH+ = Ionized; water soluble; conjugate acid

Question 31

what is teh general rule for all acid problems

Answer 31

like + like = non-ionized

Question 32

Weak Bases: Weak Bases become more _____ as pH increases (H+ decrease)

Answer 32

non-ionized

Question 33

Weak Bases: Base + base = ?

Answer 33

Base + Base = non-ionized

Question 34

Weak Bases: the pKa of a weak base is what?

Answer 34

the pH at which 50% of the Weak Base is in the ionized and 50% of the base is in the non-ionized form Ex- Lidocaine has pKa of 7.7 is the pH is 7.7, 50% of the lidocain is non-ionized and 50% of the lidocaine is ionized but is the lidocaine is injected into a pH of 7.4 less than 50% (24% in this case) will be in the non-ionized form

Question 35

Weak Bases: is the pKa different for different Weak Bases?

Answer 35

yes one Weak Base may have a pKa of 2.6 while another may have a pKa of 9.8. a given Weak Base may have any pKa, however the pKa is constant for a given Weak Base

Question 36

Weak Bases: what drugs are weak bases? and how to remember

Answer 36

think of LA and you use them for a BLOK Benzos LA Opioids Ketamine

Question 37

what drugs are weak acids again?

Answer 37

Thiopental Propofol Barbs

Question 38

Weak Bases: how do you set up the line to determine if the drug will be more ionied or unionized

Answer 38

draw your line just as you did for the weak acids but remember like + like = non-ionized so for the acid we placed non-ionized on the acidic side... this time with Weak Bases we put the non-ionized on the basic side

Question 39

Weak Bases: say you gave drug V and its a benzo. with a pKa of 9.1 state if the drug will be more ionized or non-ionized do it in order 1,2,3

Answer 39

more ionized

Question 40

Weak Bases: say you gave drug V and its a benzo. with a pKa of 4.5 state if the drug will be more ionized or non-ionized do it in order 1,2,3

Answer 40

more non-ionized

Question 41

Weak Bases: the pKas of LA range from 7.6 to 9.1, which LA will be the most NON-IONIZED at a pH of 7.4, the one w/ a pKa of 7.6 or the one with a pKa of 9.1?

Answer 41

the one with a pKa of 7.6

Question 42

for all weak acid and weak base questions what is the equation name that is utilized to calculate the answer

Answer 42

Henderson-Hasselbach equation

Question 43

Trapping of LA in Fetal Circulation: why does this occur?

Answer 43

the pH of the fetus is lower than the pH of the mom. The NON-ionized form of circulating LA crosses the placenal barrier once in the fetus, equilibrium b/t ionized and non-ionized drug is re-established B/c fetl pH is lower than mom's, however a greater amount of the drug is ionized the ionize form of the LA cannont cross the placental barrier, hence the LA is trapped in the fetus

Question 44

Trapping of LA in Fetal Circulation: picture to illustrate

Answer 44

Question 45

Trapping of LA in Fetal Circulation: the (higher or lower) the fetal pH, the greater the amount of LA in the ionizied form in teh fetus (aka greater the ion trapping)

Answer 45

Lower

Question 46

Trapping of LA in Fetal Circulation: what combination will most facilitate trapping of LA by the fetus? 1. Maternal ALKalosis and Fetal ALKalosis 2. Maternal ALKalosis and Fetal ACIDosis 3. Maternal ACIDosis and Fetal ALKalosis 4. Maternal ACIDosis and Fetal ACIDosis

Answer 46

2) Maternal ALKalosis and Fetal ACIDosis

Question 47

Trapping of LA in Fetal Circulation: What condition most prevents passage of LA from the fetus to the mom 1. Maternal ALKalosis 2. Maternal ACIDosis 3. Fetal ALKalosis 4. Fetal ACIDosis

Answer 47

4) Fetal ACIDosis

Question 48

Weak acid and Weak Base problems: Sauvage sulfate has a pKa of 4.5. will this drug be more than 50% of less than 50% non-ionized at physiological pH (7.4)?

Answer 48

more than 50% will be non-ionized

Question 49

Weak acid and Weak Base problems: Sodium Schaus has a pKa of 3.8. wll this drug be more than 50% or less than 50% IONIZED at pH 7.4

Answer 49

more than 50% will be IONIZED

Question 50

Weak acid and Weak Base problems: Propofol has pKa of 11. is it a weak acid or weak base?

Answer 50

weak acid

Question 51

Weak acid and Weak Base problems: if you see one of the following salts: Sodium drugs, Ca++ drugs, Magnesium drug are the weak acid or bases?

Answer 51

Weak acids (think of Sodium thiopental)

Question 52

Weak acid and Weak Base problems: if you see one of the folloowing salts: chloride, sulfate is it weak acid or base

Answer 52

Weak base think of morphine sulfate