L20 - Drug Solubility And Dissolution Rate 5 Flashcards

1
Q

What are non-ionic surfactants? (3)

A
  • hydroxyl and ether groups
  • less polar than ionised groups
  • need more units to produce an effective polar moeity
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2
Q

What is linked to POE chains with 20 or more ether groups?

A

Non-polar moiety
- several POE chains linked to cyclic sugar (sorbitan), linked to an alkyl group

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3
Q

What does the POE (number) equal?

A

(Number) of monomeric POE groups in the molecules

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4
Q

What are the surfactant applications? (4)

A
  • anionic
  • cationic
  • nonionic
  • parenteral
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5
Q

What are the anionic surfactant applications? (3)

A
  • used bc cheap
  • toxicity: only external use
  • O/W emulsifiers
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6
Q

What are the cationic surfactant applications? (3)

A
  • disinfectant, preservative applications
  • O/W emulsifiers
  • toxicity
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7
Q

What are the nonionic surfactant applications? (3)

A
  • O/W and W/O emulsifiers
  • low toxicity and irritancy
  • oral and parernteral use
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8
Q

What are the parenteral surfactant applications? (1) + (4)

A

Ionic
- hemolysis of RBC and destruction of T lymphocyte cells

Nonionic
- phospholipids, lecithin <= 5%
- polysorbates 80 < 2%
- cremophor EL anaphalactyc shock
- toxicity of nonionic related to residual contamination of ethylene oxide

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9
Q

What are the hydrophobic portion of surface active drugs?

A

Aromatic or heterocyclic ring system

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10
Q

What are the examples of hydrophobic portions of surface active drugs? (4)

A
  • tranquilizers, chlorpromazine
  • antidepressants, imipramine
  • antihistamines, diphenydramine
  • antibiotic, penicillin G
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11
Q

What is solubilisation?

A

Process by which, water-insoluble or partly-soluble substances are brought into aq solution by incorporation into micelles

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12
Q

What are the part of micelle like in solubilisation? (3)

A
  • Palisade layer - CHO + polar moieties + some water
  • Core - CHO moieties of the S
  • Surface or mantle - polar head groups + water
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13
Q

What does the site of solubilisation depend on?

A

The chemical nature of the solubilisate

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14
Q

The more polar the solute, the more likely to…

A

Be solublised close to the surface

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15
Q

The polar region of a non-ionic micelle is…

A

Significantly larger than that of an ionic micelle

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16
Q

What is the solubilisation capacity? What does it measure?

A

Solubilisation ratio and efficiency

  • measures the ability of a surfactant to solubilise a solute
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17
Q

What is the molar solubilisation capacity (k)?

A

The number of moles of solute that can be solubilised by 1 mole of micellar surfactant

18
Q

What is the eqn for k?

A

K = Stotal - Swater / Csurfactant - CMC

Sm = molar solubility of the solute in the micelle
Cmic = molar conc of micellar surfactants

19
Q

What are non polar region directly related to?

A

Solubilisation capacity of low polarity solutes

20
Q

How are nonpolar regions directly related to the solubilisation capacity of low polarity solutes? (3)

A

Increase HC chain
- larger nonpolar region - solubilise more solute
- decreased cmc

Introduction of a polar group, db in the chain
= decrease length of the chain

Branched surfactants
- smaller micelles

21
Q

What are the 4 things selected for during surfactant selection?

A
  • amount of surfactant that can be placed in water
  • ability to solubilise a solute
  • inc chain length = dec cmc and solubility
  • balance required in practice
22
Q

What are very long chains like as surfactants?

A

Not effective
- low solubility

23
Q

What are very short chains like as surfactants? (2)

A
  • solubilise a solute
  • very high cmc
    (Require high [surfactant])
24
Q

What does a reduction of CMC corresponde to?

A

Decrease in surfactant solubility
- reduces the amount of surfactant that can be used

25
What does an increase in chain length in two carbons lead to?
Decrease solubility 10 fold
26
What are surfactants like in practice?
- 12-16 C or 18 with db = provides low CMC, sufficient water solubility
27
What does the lipophilic part limit and what must the hydrophile provide?
- solubility in water - enough interaction with water to bring the insolible lipophile into solution
28
What happens as chain length increases? (2)
- solubility decreases - surface activity becomes more pronounced
29
The longer the HC chain, the…
Greater the tendency of the surfactant molecules to adsorb at the surface = lower the surface tension
30
What is lundelius’s rule?
Any factor that tens to decrease solubility of the surfactant promotes surface activity
31
What does a high HLB number indecate?
A surfactant exhibiting mainly polar or hydrophilic properties
32
What does a low HLB numbers represent?
Lipophilic or nonpolar properties
33
What does a mixture of high and low HLB surfactants sometimes give greater of?
Stability than single surfactant
34
What is the HLB of a mixture of surfactants eqn?
HLBmixture = x HLBA + (1-x)HLBB X - fraction of surfactant A, having HLBA (1-x) - fractoin of surfactant B, habing HLBB
35
What does the addition of a surfactant reduce?
the interfacial tension between oil and water
36
How are surfactants used for emulsions?
To stabalise them = emulgent
37
What does each type of oil require?
An emulgent of a particular HLB number in order to ensure a stable emulsion - to form stable w/o or o/w = required HLB
38
Why does the HLB of an emulsifier vary in temp?
The relative solubilities of the lipophile and hydrophile parts vary with temp
39
When is the effect of temp on the HLB of an emulsifier more pronounced?
When it’s for nonionic surfactants - their solubility depends on H bonding
40
What are H bonds like at higher temps, what does this cause the emulsifier to be? (2)
- H bonds are weakened by thermal forces - emulsifiers are less soluble in water
41
What are common nonionic emulsifiers? (2)
- water soluble at low T, stabilise o/w emulsions - oil soluble at high T, stabilise w/o emulsions
42
What is the PIT of an emulsifier?
T at which it changes from being an o/w emulsifier to an w/o emulsifier - hydrophilic and lipophilic nature just balance