Weak Acids and weak Bases Flashcards Preview

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Flashcards in Weak Acids and weak Bases Deck (52)
1

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

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

2

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

non-ionized

ionized 

3

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

non-ionized

ionized

4

the pKa is your reference what is it?

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)

5

why is the pH of the target solution inportant to know 

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

6

which is the active part? ionized or non-ionized

non-iionized

7

what are examples of weak acids?

thiopental 

Barbiturates

propofol

8

Weak Acids:

what do they do with the H+ ion

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

9

Weak Acids:

whay are they called Weak Acids

acids give up hydrogen

called weak b/c they don't dissociate completly

10

Weak Acids:

ex

Hbarb = weak acid; non-ionized; lipid soluble

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

11

Weak Acids:

pH = what?

pH = pKa

12

pH of body for all problems unless otherwise stated

7.4

13

Weak Acids:

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

become more non-ionized

 

14

Weak Acids:

Acid + Acid = 

nonionized

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

15

Weak Acids:

the pKa of a Weak Acids is what?

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 

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? 

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

17

Weak Acids:

are the pKa's different for different Weak Acids?

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

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

Non-ionized

Non-ionized

19

Weak Acids:

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

acid

conjugate base

20

Weak Acids:

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

  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

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

 

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

more NON-ionized

23

Weak Acids:

assume drug Y is a barb

state if the drug has more ionized or non-ionized

do steps 1, 2, 3

More IONIZED

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

 

non-ionized

25

Weak Acids:

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

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

 

26

Weak Acids:

should you mix thipoental with a low pH solution? explain

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

27

Weak Acids:

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

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

28

Weak Bases:

weak bases do what with H+

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

29

Weak Bases:

picking up a H+ (proton) means it becomes pronated or ___-

charged

30

Weak Bases:

label what is non-ionized

 

LA = Lipid soluble, NON-ionized; weak base

H+ = base

LAH+ = Ionized; water soluble; conjugate acid

31

what is teh general rule for all acid problems

like + like = non-ionized

32

Weak Bases:

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

non-ionized

33

Weak Bases:

Base + base = ?

Base + Base = non-ionized

34

Weak Bases:

the pKa of a weak base is what?

 

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

 

35

Weak Bases:

is the pKa different for different Weak Bases?

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

36

Weak Bases:

what drugs are weak bases? and how to remember

think of LA and you use them for a BLOK

Benzos

LA
Opioids

Ketamine

37

what drugs are weak acids again?

Thiopental

Propofol

Barbs

38

Weak Bases:

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

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 

 

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

 

more ionized

 

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

 

more non-ionized

 

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?

the one with a pKa of 7.6

42

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

Henderson-Hasselbach equation

43

Trapping of LA in Fetal Circulation:

why does this occur?

 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

44

Trapping of LA in Fetal Circulation:

picture to illustrate

 

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)

Lower

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

 

 

 

2) Maternal ALKalosis and Fetal ACIDosis

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

4) Fetal ACIDosis

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)?

more than 50% will be non-ionized

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

more than 50% will be IONIZED

50

Weak acid and Weak Base problems:

Propofol has pKa of 11. is it a weak acid or weak base?

weak acid

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?

Weak acids

(think of Sodium thiopental)

52

Weak acid and Weak Base problems:

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

Weak base 

think of morphine sulfate 

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