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a. SL12102: The science of medicines > L20 - Drug Solubility And Dissolution Rate 5 > Flashcards

L20 - Drug Solubility And Dissolution Rate 5 Flashcards

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1
Q

What are non-ionic surfactants?

A
  • hydroxyl and ether groups
  • less polat than ionised groups
  • need more units to produce an effective polar moeitu
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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?

A
  • anionic
  • cationic
  • nonionic
  • parenteral
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5
Q

What are the anionic surfactant applications?

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

What are the cationic surfactant applications?

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

What are the nonionic surfactant applications?

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?

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?

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?

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 direcly realted to the solubilisation capcity of low polarity solutes?

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?

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
Q

What does an increase in chain length in two carbons lead to?

A

Decrease solubility 10 fold

26
Q

What are surfactants like in practice?

A
  • 12-16 C or 18 with db
    = provides low CMC, sufficient water solubility
27
Q

What does the lipophilic part limit and what must the hydrophile provide?

A
  • solubility in water
  • enough interaction with water to bring the insolible lipophile into solution
28
Q

What happens as chain length increases?

A
  • solubility decreases
  • surface activity becomes more pronounced
29
Q

The longwe the HC chain, the…

A

Greater the tendency of the surfactant molecules to adsorb at the surface
= lower the surface tension

30
Q

What is lundelius’s rule?

A

Any factor that tens to decrease solubility of the surfactant promotes surface activity

31
Q

What does a high HLB number indecate?

A

A surfactant exhibiting mainly polar or hydrophilic properties

32
Q

What does a low HLB numbers represent?

A

Lipophilic or nonpolar properties

33
Q

What does a mixture og high and low HLB surfactants sometimes give greater of?

A

Stability than single surfactant

34
Q

What is the HLB of a mixture of surfactants eqn?

A

HLBmixture = x HLBA + (1-x)HLBB

X - fraction of surfactant A, having HLBA
(1-x) - fractoin of surfactant B, habing HLBB

35
Q

What does the addition of a surfactant reduce?

A

the interfacial tension between oil and water

36
Q

How are surfactants used for emulsions?

A

To stabalise them
= emulgent

37
Q

What does each type of oil require?

A

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
Q

Why does the HLB of an emulsifier vary in temp?

A

The relative solubilities of the lipophile and hydrophile parts vary with temp

39
Q

When is the effect of temp on the HLB of an emulsifier more pronounced?

A

When it’s for nonionic surfactants
- their solubility depends on H bonding

40
Q

What are H bonds like at higher temps, what does this cause the emulsifier to be?

A
  • H bonds are weakened by thermal forces
  • emulsifiers are less soluble in water
41
Q

What are common nonionic emulsifiers?

A
  • water soluble at low T, stabilise o/w emulsions
  • oil soluble at high T, stabilise w/o emulsions
42
Q

What is the PIT of an emulsifier?

A

T at which it changes from being an o/w emulsifier to an w/o emulsifier

  • hydrophilic and lipophilic nature just balance

a. SL12102: The science of medicines (26 decks)

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