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Pharmaceutics 2 > 3 - Solubility > Flashcards

3 - Solubility Flashcards

1
Q

Why is preparation of a solution dose form often problematic?

A

many drugs have limited water solubility

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2
Q

positive heat of solution = ?

A

increase solubility with increase in temperature

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3
Q

negative heat of solution = ?

A

decrease solubility with increase in temperature

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4
Q

solubility of a substance at a stated temp is a _____

A

constant

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5
Q

If something is very soluble, the amount of solvent required per part of solute = ?

A

<1

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6
Q

If something is practically insoluble the amount of solvent required per part of solute = ?

A

<10,000

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7
Q

Acidic drugs don’t ____ in acidic media

A

ionize

majority will be in unionized form

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8
Q

Basic drugs don’t ____ in basic media

A

ionize

majority will be in unionized form

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9
Q

Like dissolves ____

A

like

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10
Q

We would expect organic molecules to be more soluble in ______ solvents than water

A

organic

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11
Q

Molecules with functional groups like OH will confer ____ solubility to an organic molecule

A

water

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12
Q

Inorganic molecules - Water solubility:

-If both the cation and anion are ____ the compound is soluble.

A

monovalent

ex.
NaCl
LiBR
NH4NO3

(all of these have only a charge of +1 or -1)

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13
Q

Inorganic molecules - Water solubility:

If ___ of the ions in a salt is monovalent the compound is soluble.

A

one

ex.
BaCl2
Na2SO4
Na2PO4

(only one of the ions in a salt needs to be monovalent for it to be soluble)

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14
Q

Inorganic molecules - Water solubility:

If both the anion and cation are _____ the compound will have limited water solubility.

A

multivalent

ex.
CaSO4
BaSO4

exceptions:
ZnSO4
FeSO4

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15
Q

Inorganic molecules - Water solubility:

Salts of alkali metals (K, Na, Li, Cs) and ____ are water soluble.

A

ammonia

ex.
Na2CO3
Na2HPO4
LiSO4

exception
Li2CO3

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16
Q

Inorganic molecules - Water solubility:

nitrates, sulfates, and halides are ____ soluble

A

water

exceptions
AgCL2
BaSO4

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17
Q

Inorganic molecules - Water solubility:

_____ and _____ are not water solbule

A

hydroxides
oxides

(except for hydroxides and oxides with alkali metals and ammonium salts)

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18
Q

Inorganic molecules - Water solubility:

phosphates, carbonates, silicates, borates are all _____

A

insoluble

except for those with alkali metals and ammonium

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19
Q

Organic molecules - Water solubility:

Molecules have one POLAR functional group are usually soluble to chain lengths of ___ carbons

A

five

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20
Q

Organic molecules - Water solubility:

Molecules with ____ chains are more soluble than the corresponding ____ chain compound

A

branched > straight

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21
Q

Organic molecules - Water solubility:

Water solubility _____ with increasing molecular weight.

A

decreases

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22
Q

Generally a drug must be in solution before it is able to be ____ into the blood stream

A

absorbed

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23
Q

For liquid dose form ___ solubility is desirable so a dose of drug is in a reasonable volume.

A

water

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24
Q

FDA introduced ?? for oral drug products

A

biopharmaceutics classification system (BCS)

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25
Q

Explain BCS (biopharmaceutics classification system)

A

drugs are classified into four groups based on solubility and ability to permit membranes

26
Q

When is a drug considered highly soluble?

A

When the highest dose strength is:

  • soluble in <250 mL water
  • soluble over a pH range of 1-7.5
  • highly permeable when the extent of absorption is >90% of an administered dose
27
Q

Explain Class I - IV for BCS

A

Class I:

  • good solubility, good permeability
  • few problems

Class II:

  • bad solubility, good permeability
  • rate-limiting step for bioavailability is solubility/dissolution

Class III:

  • good solubility, bad permeability
  • rate-limiting step for bioavailability is crossing biological membranes

Class IV:

  • bad solubility, bad permeability
  • drug has a lot of problems
28
Q

What must the D:S (dose:solubility) ratio be for an oral dose ?

A

<250mL
* 100 mL volume would be okay to use as an oral dose form

*because stomach fluid is about 250 mL

29
Q

What must the D:S (dose:solubility) ratio be for an eye drop dose ?

A

< 0.02 mL

*because lacrimal fluid is about 20 microL (0.02 mL)

30
Q

What must the D:S (dose:solubility) ratio be for a nasal dose ?

A

<0.3 mL

*because nasal fluid is about 0.3mL

31
Q

What must the D:S (dose:solubility) ratio be for a sublingual dose ?

A

<5 mL

32
Q

What must the D:S (dose:solubility) ratio be for a vaginal tablet dose ?

A

<5 mL

33
Q

What must the D:S (dose:solubility) ratio be for an inhaled dose ?

A

<0.5 mL

34
Q

If a drug molecule contains _____ functional groups the solubility may be managed by controlling the ___ of the vehicle being used.

A

ionizable

pH

35
Q

Most drug products are formulated between pH values of ___ for biocompatibility.

A

4-8

36
Q

If a drug is ____ it is more water soluble

A

ionized

worse at crossing membranes

37
Q

If a drug is more _____ it is insoluble in water

A

unionized

better at crossing membranes

38
Q

see slide 26 fo sho

A

ok gangsta sam

39
Q

What is a salt?

A

The product of an ionizable drug with an ionizable counter-ion of opposite charge.

(ionic compound)

40
Q

Most common reason for using a salt form?

A

enhanced solubility?

leading to improved bioavailability?

-could be helpful in masking an unpleasant taste

41
Q

For counter-ion selection, the pKa of the conjugate base should be ___ than the conjugate acid.

A

greater

difference of 3 or more pKa units is common

42
Q

Explain the common-ion effect

A

Its when there is a reduction in solubility of a compound when putting it into a solution that contains one of the same ions as the compound.

ex. putting NaCl into the stomach (where gastric acid HCl is present)
- this reduces solubility of NaCl because there is already a lot of Cl- present.

As counter-ion [Cl-] increases the concentration of [H+] has to decrease to keep Ksp at a constant.

So the solubility of NaCl is decreased to the rate that [H=] is decreasing

43
Q

When are cosolvents used?

A

when the parenteral drug product has limited water solubility

44
Q

Examples of some cosolvents

A

glycerin
alcohol
propylene glycol
polyethylene glycol

45
Q

_____ _____ and _____ are extremely toxic and must never be used in pharmaceutical products

A

ethylene glycol

methanol

46
Q

Solubility is largely a function of what?

A

the polarity of the solvent

47
Q

What do polar solvents dissolve?

A

ionic and other polar solutes

48
Q

What do non-polar solvents dissolve?

A

non-polar solutes

49
Q

What do semi-polar solvents (like alcohol) do?

A

they may induce a degree of polarity in non-polar molecules and improve their water solubility

50
Q

What is the dielectric constant?

no units

A

a measure of the effect of solvent on potential energy of interaction between two charges

a measure of how effective the material is as an electrical insulator

the ability to keep two charges separate

51
Q

Water as a very ____ dielectric constant

A

high

52
Q

benzyl alcohol is toxic to ??

A

babies

53
Q

____ products rarely contain cosolvents

A

ophthalmic products

too dangerous to use any products even with only small potential toxicity

54
Q

What are surfactants?

A

molecules with polar and non-polar regions

55
Q

Non-polar region of a surfactant is usually a ______ segment

A

hydrocarbon

56
Q

Polar region of a surfactant is ??

A

may be anionic, cationic, or non-ionic

57
Q

As [surfactant] increases the surfactant will associate into soluble structures known as _______

A

micelles

58
Q

What is critical micelle concentration? (CMC)

A

the concentration where the micelles begin to form

59
Q

complexing agents

A

involves incorporating drug within the completing agent so that the outer hydrophilic groups of the agent interact with water and make whole complex soluble

ex. caffeine benzoic acid mixture
ex. amphotericin-B complex with sodium cholesterol sulphate (lipid complex)

60
Q

What are cyclodextrins?

A

molecules composed of 6, 7, or 8 glucopyranoside units joined through 1-4 bonds

61
Q

Cyclodextrins have _____ interior

A

lipophilic

62
Q

Cyclodextrins have _____ exterior

A

hydrophilic (due to hydroxyl groups)

Pharmaceutics 2 (5 decks)

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