Lecture 2: Ionization of Drugs Flashcards

1
Q

Ionization state

A

-impacts solubility, absorption, binding to receptor

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2
Q

Charged molecules

A

more soluble, less likely to cross lipid membranes

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3
Q

pH

A

affects ionization
HA –> A- + H+
BH+ –> B + H+

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4
Q

Ionizable functional groups

A

-weak acids and bases

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5
Q

Ionizable groups with pKa < 7

A

-arylcarboxylic acid
-arylamine
-aromatic amines
-alkylcarboxylic acid

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6
Q

ionizable groups with pKa > 7

A

-alkyl amines
-phenol
-guanidine

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7
Q

nonionizable groups

A

-alkyl alcohol
-alkyl aldehyde
-ether
-ester
-ketone
-amide
-quarternary amine

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8
Q

Drug examples

A

SLIDE 6

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9
Q

Henderson-Hasselbach equation

A

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

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10
Q

when pH < pKa

A

[A-] < [HA]
-protonated

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11
Q

when pH > pKa

A

[A-] > [HA]
-deprotonated

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12
Q

when [A-]/[HA]

A

[HA] = [A-]

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13
Q

Acetaminophen

A

STRUCTURE

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14
Q

Water

A

-polar solvent that dissolves polar molecules
-H bond donors and acceptors
-ionic groups

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15
Q

Solubility

A

-like dissolves like
-can be improved by changing pH

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16
Q

1g Procaine

A

needs 200mL water

17
Q

1g procaine-HCl

A

needs 1 mL water

18
Q

At pH 7.4, what is the ratio of ibuprofen in the acid form (neutral) to
that in the base form (negatively-charged)? pKa= 4.4

19
Q

Membrane permeability

A

-GI tract, blood brain barrier, lipid membranes
-most drugs absorbed by passive diffusion

20
Q

Absorption rate

A

related to the drugs liphophilicity

21
Q

lipopholic drugs

A

absorbed more efficiently

22
Q

Transport across membrane

A

-intercellular junctions
-lipid cell membranes
-transporters
-endo and exocytosis

23
Q

Passive diffusion of ionizable drugs (cant cross lipid bilayer)

A

-more efficient at pH where drug is neutral
-even while mostly ionized it still moves through bilayer slowly
-equilibrium

24
Q

diffusion rate

A

proportional to amount of neutral drug

25
Location of absorption
-most in jejunum (pH 5-7) -acidic drugs in stomach (pH 1-3)
26
A drug is an organic base (RNH2) with a pKa of 9.0. Assume the stomach has a pH of 1.5, and the small intestine has a pH of 6.5. Where will the drug be preferentially absorbed?
Small Intestine
27
Can a drug with a permanent charge (e.g. quaternary amine) be absorbed?
No
28
Which of the following drugs is negatively charged at pH 7.4?
drugs with pKa<7.4
29
Most drugs are absorbed from the GI tract to the blood stream by _______________.
passive diffusion
30
Which of the following statements is most accurate about passive diffusion of
Eventually, the concentrations of the drug become equal in both sides of the membrane.
31
At pH 7.5, what is the ratio of this drug (pKa = 9.5) in the acid form (neutral) to that in the base form (negatively-charged)?
100:1
32
Which of the following shows a functional group whose ionization status is not affected by the pH?
quarternary amine