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Form & Tech II > Ointments and gels > Flashcards

Ointments and gels Flashcards

1
Q

What are some types of gelling agents?

A
  • Natural gums (Tragancath, carrageenan pectin, agar, alginic acid)
  • Cellulose derivatives (methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose)
  • Synthetic polymers (carbopol)
  • Clays (Bentonite, veegum, laponite)
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2
Q

What are single phase gels?

A

Gels where there are no apparent boundaries between the solid and liquid components

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3
Q

What are the dematological factors that should be taken note of when choosing a suitable base?

A
  1. Base should release drug readily to skin (partition coefficient of drug between base and skin)
  2. Base should facilitate drug absorption by skin (influenced by ability of base to penetrate and hydrate skin)
  3. Base should not interfere with normal skin functions/ cause irritation
  4. Base should be miscible and compatible with skin secretions (type and pH of base –> should be close to that of the skin)
  5. Base should have good emolliency
  6. Base should be easy to apply and remove
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4
Q

Pharmaceutical factors that should be taken into account when choosing suitable base:

A
  1. Base should be chemically and physically stable
  2. Base should have good solvent property
  3. Base should have good emulsifying property (affects ease of incorporating aq drug solutions)
  4. Base should have suitable consistency (affects drug distribution, ease of production and administration)
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5
Q

Formulation ingredients of ointments

A
  1. Lipophilic materials,
  2. Emulgents/ PEGs,/gelling agents
  3. Additives: antimicrobial preservatives, antioxidants/chelating agents, buffers, fragrance, colours
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6
Q

what are some special types of ointments?

A

Ophthalmic and rectal ointments

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7
Q

what are the techniques used in the incorporation method of preparing ointments?

A
  1. Mixing small amounts of base with small amounts of drug then mix all the mixtures together into one large mixture
  2. Incorporate small amounts of base into the solid drug multiple times till base is used up (geometric dilution)
  3. For liquid drug add the drug to the base repeatedly till all drug is used up
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8
Q

What are the steps needed to prepare non-emulsion bases using fusion method?

A
  1. ointment components are melted together and cooled with constant stirring until congealed
  2. Drug may be added during/after preparation of ointment base. If the drug is thermolabile, add the drug after base is formed –> need to make sure that the drug is uniformly distributed in base
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9
Q

What are the steps needed to prepare emulsion bases using fusion method?

A
  1. incorporate oil-soluble and water-soluble components with oil and water phases respectively
  2. Mix the two phases separately at around 70ºC and blend the two phases together
  • The drug is added to the phase in which it has higher solubility.
  • Volatile materials should only be added in after ointment base has cooled down
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10
Q

How to make a gel using direct hydration?

A
  1. Add gelling agent to dispersion medium slowly and gradually under stirring
  2. Dispersion may be facilitated by agitation/ temperature modification of dispersion medium
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11
Q

Properties of ointment base and drug that affect drug bioavailability to skin

A
  1. Type of ointment base: absorption enhanced by bases that easily cover skin and mix readily with sebum (vegetable oils/animal fat) or bases increasing skin hydration (water migrates to the stratum corneum to increase intercellular space for drug entrance)
  2. Consistency of ointment base (if increased, diffusion decreased, resulting in reduced absorption)
  3. Interaction between ointment base and drug
  4. Partition coefficient of drug between the base and skin (drug should have certain degree of solubility in both water and oil in order to penetrate skin –> log P ~2–> tendency of drug to leave base)
  5. Charges on drug molecules (ions less permeable than neutral molecules –> base usually formulated such that pH comparable to skin)
  6. Size of molecules (cut off at 400)
  7. amount of drug in ointment base (concentration of drug available for absorption)
  8. Presence of penetration enhancers in ointment base (affect permeability of skin through chemical insult, skin hydration and/or reduction of surface tension)
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12
Q

What are some ways in which ointments can be evaluated?

A
  1. Penetration of ointment base into skin
  2. Drug release from ointment
  3. Absorption of drug into bloodstream
  4. Irritant effects
  5. Physical and chemical stability
  6. Microbial quality (includes preservative efficacy) –> just refer to slide 76
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13
Q

How are irritant effects measured?

A
  1. Draize dermal irritation test in rabbits
    ointment repeatedly applied to clipped skin of rabbit’s back –> terminated when intense redness with inflammation observed –> measure number of applications. The higher the number, the lower the irritation score
  2. 21-day cumulative irritation study
    Ointment applied to same site repeatedly and tape is used to occlude skin –> typical erythema score given. If intense erythema with edema and vesicular erosion, terminated before 21 days up, given score of 4
  3. Use of embryonated egg
    Inject ointment into chorioallantoic membrane and look at the reaction of blood vessels –> if become thicker, indication of irritation and inflammation
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14
Q

How to measure absorption of drug into bloodstream?

A
  1. ointment applied to skin

2. blood/urine obtained over time for drug assay

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15
Q

BP and USP methods for determining preservative efficacy of ointments

A

Test organism incorporated into ointment in container –> incubate inoculated ointment –> withdraw aliquot sample and determine number of viable cells at 0 hr and other appropriate intervals (2, 7, 14, 28 days) –> log reduction factor obtained should not be less than the volume stated in the table (slide 78)

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16
Q

What are ointments?

A
  • Homogenous semi-solid preparations usually consisting of solutions/dispersions of >1 active ingredients in suitable bases
  • Usually applied to skin/certain mucous membranes for emollient, protective, therapeutic/prophylactic purposes where degree of occlusion desired
  • Has cooling and soothing effect
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17
Q

What are absorption bases?

A
  • Bases that have an ability to absorb quantities of water and retain ointment-like consistency
  • Do not contain water as components in basic formula
  • Generally composed of oleaginous base incorporated with hydrophilic substances
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18
Q

What are some ways to classify ointment bases

A
  1. Composition of bases

2. Degree of penetration

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19
Q

What are the types of ointment bases in terms of composition of base?

A
  1. Oleaginous bases: Entirely lipophilic
  2. Absorption bases: Can absorb water
  3. Emulsion bases: semi-solid emulsions or creams
  4. Water-soluble bases
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20
Q

What are the properties of oleaginous bases?

A
  1. Greasy (can stain clothes and cause edema)
  2. Occlusive (good as emollients)
  3. Non-hydrophilic
  4. Non-water removable( good for drugs prone to hydrolysis)
  5. Anhydrous
21
Q

Wool fat is an example of absorption base. What is one potential problem of wool fat?

A

Allergy, as wool fat is a substance secreted by the sebaceous glands of animals with wool, and not everyone can tolerate

22
Q

What are the properties of absorption bases?

A
  1. Greasy
  2. Occlusive
  3. Insoluble in water
  4. Absorb water
  5. Anhydrous
23
Q

What is the function of humectants in vanishing creams?

A

Prevent excessive loss of water during shelf life of cream. This prevents the cream from getting too dry and getting difficult to apply

24
Q

Identify which ingredient in the following formula for vanishing cream act as the oil base:

  • Stearic acid 20%
  • KOH 1.4%
  • Glycerin 10%
  • Water to 100%
A

Stearic acid is the oil base

  • Some react with KOH to form K stearate, a soap which help to form emulsifying agent
25
Q

Cold cream is an example of ________ emulsion base, and forms an occlusive layer of oil/fat on the skin which ______________

A
  • Water in oil

- prevent skin from becoming dry

26
Q

What are the properties of emulsion bases?

A

For o/w

  1. Hydrophilic
  2. Insoluble in water
  3. Water-removable
  4. Non-greasy
  5. Non-occlusive
  6. Poor emollient

For w/o –> Opposite

27
Q

PEGs are an example of what type of bases

A

Water-soluble bases

28
Q

What are some advantages of PEGs as ointment base?

A
  1. Inert and non-irritating to skin

2. Does not support mould growth

29
Q

“…blends of PEG are used to produce base with desired consistency”

What does “consistency” mean in this context?

A

How easily the base can spread. It is a term for semi-solid or solid state of matter (similar to viscosity of liquid state of matter)

30
Q

What are some properties of PEG bases?

A
  1. Anhydrous
  2. Hydrophilic
  3. Water-soluble
  4. Water-removable
  5. Non-greasy
  6. Lipid-free
  7. Non-occlusive
31
Q

What is a good application of PEG bases?

A

Since they are water-soluble, they can be formulated into a product applicable to hairy regions as they are removed easily by water (e.g. scalp)

32
Q

What are gels?

A

Semi-solids consisting of solid component enclosing and interpenetrated by liquid component

  • Solid component usually large organic molecules or small inorganic particles
  • Liquid component is either water or organic solvent
33
Q

What are the properties of the solid component in single-phase gels?

A
  1. Lyophilic - Dispersed readily in dispersion medium

2. Are large organic molecules that exist as “strands” in the gel

34
Q

The rigidity of the single-phase gel is attributed to ___________

A

interwining network which traps and holds the dispersion medium

35
Q

What is one important property gels must posess?

A

Changes due to stress (like temperature or agitation) should be reversible

i.e. change between semi-solid and liquid

36
Q

What are the properties of the solid component in two-phase gels?

A
  1. Lyophobic - does not disperse readily in dispersion medium
  2. Small inorganic molecules
  3. Particles exists as floccules in the gel
37
Q

What is Sol-Gel transformation

A

The phenomenon describing the reversible transition between semi-solid and liquid state of gels

E.g. Thermal gels (MC, gelatin), thixotropic gels (bentonite)

38
Q

Gels can absorb water with significant and insignificant increase in volume. What are the 2 terms used to describe the volume changes?

A

Swelling, Imbibition

39
Q

A gel exhibits syneresis. What does this mean?

A

Gel shrink on storage, causing some liquid to be squeezed out

40
Q

General indication for ointment bases?

A
  1. Vehicle for drug to be applied on skin

2. Emollient

41
Q

What are some features of topical drug therapy?

A
  1. Drug must reach skin surface at adequate rate and concentration
  2. Greatest resistance to drug penetration exerted by stratum corneum
  3. Drug absorption is enhanced by hydrating the stratum corneum
  4. Drug absorption through walls of hair follicles, weat glands and oil glands is less significant
42
Q

Describe the 2 routes of drug penetration through the stratum corneum

A
  1. Intercellular route: spaces between cells, but filled with fluids, lipids and surface-active compounds
  2. Transcellular route
43
Q

When is fusion method of making ointment recommended?

A

When heating is required, especially when components with high MW are used

44
Q

Two methods used to prepare gels

A
  1. Direct hydration

2. Special individualised procedures (e.g. AlOH3 gel using chemical reaction)

45
Q

In the packaging and storage of ointments, why are tubes are generally preferred over jars?

A
  1. More convenient, less messy
  2. Less exposed to contamination due to lesser exposure to air
  3. Smaller amount of ointment inside each tube limit number of applications to reduce in-use contamination
46
Q

What are other considerations in the packaging and storage of ointments?

A
  1. If components are photosensitive, opaque packaging is required
  2. Whether any components in the ointment may interact with the walls of the packaging

(help me add more thanks lol)

47
Q

How is the penetration of ointment base into skin measured?

A
  • Leave a pre-weighed ointment on skin for a period of time, then remove the ointment
  • Weigh before and after applying to skin, and find the difference in weight, which is the amount absorbed by the skin
48
Q

Why must the method used to determine drug release from ointment be stated?

A
  • Different method gives different release rate due to nature of experiment
49
Q

Typical erythema scores indicate the severity of skin reaction to an ointment. What do each score represent?

A

0: No visible reaction
1: Mild erythema
2: Intense erythema
3: Intense erythema with edema
4. Intnse erythema with edema and vesicular erosion

Form & Tech II (6 decks)

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