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PHARM 124 Final > Semisolids > Flashcards

Semisolids Flashcards

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1
Q

Identify the layers of the skin and their main functions. Which layer represents the main
skin barrier?

A

Epidermis

Stratum corneum (horny layer)
– the main barrier **controls percutaneous
absorption (dead corneocytes)
Stratum lucidum (clear layer) transitionary layer
Stratum granulosum (granular layer)
- Keratinocytes contain keratohyalin granules
which discharge a cement-like substance that bind cells together (barrier against
foreign material); Site of biochemical activity (bioreactor)
Stratum spinosum (prickle cell layer)
- Keratinocytes contain bundles of filaments
(“prickly” looking) which help skin to resist abrasion
Stratum germinativum/basale (basal layer)
- Nucleated basal cells , dividing
(mitosis) layer which replaces the shedding cells of stratum corneum)

Dermis
– sensation, blood circulation, immune function
- Site for drug metabolism
- Hair follicles, sebaceous glands, sweat glands (appendages)

Subcutaneous tissue – support, mechanical cushioning, thermal barrier, subcutaneous tissue

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2
Q

What is the skin surface pH? Define acid mantle.

A

5.5

Acid mantle pH 4.2 - 5.6 → bacteriostatic and fungistatic secretions (short chain fatty acids from
sebaceous and eccrine sweat glands) – formulations with pH 5.5 are said to be the most compatible with the skin

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3
Q

What is the average thickness of the layers of skin

A

Epidermis: 200 microm (800microm thick skin, 60 microm eyelid)
Stratum corneum: 10-20 microm

Dermis: 1-5 mm

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4
Q

What is percutaneous absorption influenced by?

A
  • Blood vessels: maintain sink conditions; vasoconstriction and vasodilation due to cold
    and heat decreases or increases drug absorption, respectively
  • Appendages: pores of appendages can allow drug absorption, however, this ‘shunt route’
    provides for very low absorption due to the small fraction of area (0.1% of total area)
    occupied by hair follicles and glands
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5
Q

What is water content of the normal stratum corneum

A

10-20%

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6
Q

What does the shunt route of drug permeation mean?

A

Shunt route = absorption through the appendages

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7
Q

What effect does UV light have on the skin?

A

UVB 290 - 320 nm ⇒ burns skin
UVA 320 - 400 nm ⇒ less damaging (aging, pigmentation
skin response to UV radiation (Pigmentation, erythema, aging, malignancy)

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8
Q

The skin is an important heat barrier:
What is the consequence of heat or cold exposure on the skin vasculature and percutaneous absorption?

A

Heat conservation (vasoconstriction, shivering, goose bumps, cold)
- percutaneous absorption decreases

  • Heat loss (vasodilation, skin reddening)
    percutaneous absorption increases
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9
Q

Define “sink conditions”

A

Blood circulation in the DERMIS maintains sink conditions by taking up drug absorbed into skin
into the systemic circulation thereby maintaining high concentration gradient between the
formulation and the skin

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10
Q

Define ointments, creams, pastes, gel

A

Ointment
- hydrophobic or greasy
- Anhydrous
- Single phase vehicles

Cream
- Contain both oil phase and water

Paste
- 20-50% of solids finely dispersed in a fatty vehicle

Gel
- provide stiffness to a solution or colloidal dispersion
- good for hairy areas
- water-soluble drugs

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11
Q

Which bases are non water washable bases and water washable vehicles?

A

non water washable bases
- Oleaginous/hydrocarbon bases
- Absorption bases
- W/O emulsion bases
- Silicone bases

Water washable vehicles
- O/W emulsions
- Gels
- Hydrophilic bases
- Emulsifying bases

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12
Q

Define occlusion and effects on the skin

A
  • formation of an impermeable layer on the skin to prevent evaporation of water

Effects:
- Increased hydration (by preventing evaporation of water from the skin)
- Enhanced percutaneous absorption
- Softening of the skin (emollient action)

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13
Q

What are properties of oleaginous/hydrocarbon bases?

Provide examples

A
  • Hydrophobic
  • Greasy
  • Non-water washable
  • Occlusive
  • Emollient

Excipients
- fixed oils (peanut, cottonseed, almond)
- Waxes (esters of fatty acids)

Vehicles
- Petrolatum
- Yellow, white, zinc oxide ointment

Plastibase
- polyethylene
- Mineral oil

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14
Q

What are properties of Absorption bases and give examples

A

Properties
- Hydrophobic
- Greasy
- Anhydrous (hydrophilic components provide water-absorbing properties)
- W/O after adding water

Examples
- Anhydrous lanolin (wool fat)
- Lanolin (hydrous wool fat)
- Lanolin alcohols, liquid lanolin
- Hydrophilic petrolatum
- Aquabase ointment
- Wool alcohols ointment

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15
Q

Differentiate between wool fat (anyhdrous lanolin) and lanolin

A

wool fat (anyhdrous lanolin)
- contains mixture of sterols which impact the ability to absorb water
- water content: LESS THAN 0.25%

Lanolin
- 25-30% water

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16
Q

Define cold cream and the traditional emulsifier used for it

Study These Flashcards
A

W/O emulsion bases
- contain beeswax-borax type in situ emulsifier)
- cetyl esters wax
- White wax

17
Q

What are properties of w/o emulsions non-water washable bases

Study These Flashcards
A

Properties
- more greasy
- Emollient (cleansing cream)
- Capable of absorbing oil-soluble compounds from the skin (makeup removers)

18
Q

What are properties of non-water washable pastes?

Study These Flashcards
A

Properties
- ointments containing up to 50% powder dispersed in fatty bases
- Very stiff consistency
- Form a thick impermeable layer on the skin

19
Q

What are properties for silicon bases non-water washable bases

Study These Flashcards
A
  • Used as skin barrier to protect skin
  • concentration in ointments 10-30%
20
Q

What are the properties of water washable bases

Study These Flashcards
A
  • waterwashable
  • Soft
  • Non-occlusive
  • Moisturizing
  • Penetration enhancement of the drug compounds
21
Q

Define vanishing cream and the traditional emulsifier used for it

Study These Flashcards
A
  • o/w emulsion base
  • Stearic acid and KOH form potassium stearate in situ
  • Smooth, easy to apply
  • No residue
22
Q

What does a cleansing o/w cream look like have?

Study These Flashcards
A
  • stearic acid 25g
  • mineral oil 57 g
  • lanolin 34 g
  • Triethanolamine 10g
  • propylene glycol 24 g
  • Water 150g
23
Q

What are some gel-forming materials

Study These Flashcards
A
  • Natural gums
  • Methylcellulose, hydroxymethcylcellulose etc.
  • Carbopol
  • Bentonite
24
Q

What are properties of hydrophilic bases and examples

Study These Flashcards
A
  • Anhydrous (cannot take up more than 8% water)
  • non-occlusive
  • greaseless
  • Water washable, non-irritant
  • Chemically stable: do not hydrolyze

Examples:
PEG 3350 (solid)
PEG 300 (liquid)

25
What are example of emulsifying bases?
Sodium laurylsulfate (anionic) Cetrimide (cationic) Cetomacrogol (Non-ionic)
26
What is the reason for using the following additives to dermatological vehicles? Give example for each group. Humectants Levigating agents Penetration enhancers Antioxidants Preservative
Humectants - increase skin hydration Eg. glycerol, PEG, propylene glycol Levigating agents - aid particle size reduction Eg. mineral oil, caster oil, glycerol Penetration enhancers - Temporarily increase permeability of the skin to allow drug to pass eg. chemical penetration enhancers, specialized delivery system Antioxidants - prevent rancidity due to oxidation eg. BHA, BHT, ascorbic acid, sulfites, Vitamin E Preservative - protect from microbial growth eg. alcohol, benzoic acids, quratnery ammonium compounds
27
Indicate the type of dermatological vehicle preferred in the following dermatological conditions and why: Acne Alopecia Dermatitis/Eczema Psoriasis Urticaria Herpes Corns and calluses Athletes foot
Acne - liquids, gels, creams o/w emulsion - base should NOT be occlusive (since acne is plugged pores and oily skin surface) Alopecia - water or alcohol liquids, gels, creams - Should be easy to apply on hairy areas and non-greasy (gels) Dermatitis/Eczema - creams, lotions - Base should NOT be occlusive (oozing condition) Psoriasis - Occlusive (hydrocarbons, silicon bases, creams, ointments with plastic wrap) - bases should BE occlusive and increase hydration Urticaria - gels, shake lotions, creams - NOT occlusive (should help cool and soothe burning and itching) Herpes - lotions, PEG base, gels - NOT occlusive Corns and calluses - OCCLUSIVE ointment bases - should provide softening and moisturization Athletes foot - o/w creams, powders - NOT OCCLUSIVE
28
. What type of dermatological base can be used: On oozing and weeping dermatoses? On dry scaly skin? On hairy skin?
On oozing and weeping dermatoses? Liquids, pastes, o/w creams On dry scaly skin? Ointments (all types), o/w and w/o creams, pastes, liquids On hairy skin? Gels, liquids, o/w creams
29
Describe the process of permeation of molecules?
- Governed by Fick's law - the rate limiting factor for drug diffusion is the stratum corneum - highly hydrophobic drug molecules can form a depot in the SC or dermis eg. corticosteroids
30
What layers are topical delivery vs. transdermal delivery?
Topical: epidermis, dermis transdermal: circulation (hypodermis)
31
What is the ‘brick-and-mortar’ model and how is it used to explain drug permeation?
The structure of the stratum corneum is described as brick-and-mortar where the - bricks = corneocytes (protein/cells) - mortar = lipid (between the cells) The two pathways for drug absorption are : intercellular – through the lipid channels BETWEEN the cells and intra/transcellular – THROUGH the cells
32
Indicate how the following factors influence percutaneous absorption (PA):
a. Concentration of drug in the vehicle ↑ drug conc in vehicle = ↑ PA b. Drug metabolism in the skin =↓ PA c. Vehicle-to-stratum corneum partition coefficient =↑ PA d. Ionization state of the drug non-ionized drug = ↑ PA better e. Supersaturation of drug in the vehicle by co-solvents. (hydrophilic solvents) - ↑ PA f. Presence of penetration enhancers in the vehicle - ↑ PA g. Vasodilation in dermis= ↑ PA vasoconstriction = ↓ PA h. Dry skin = ↓ PA fully hydrated skin = ↑ PA i. Age of the skin infant = more permeable adult skin = less permeable j. Different regions of the skin - permeability varies as thickness of stratum corneum varies (thin SC on eyelids, behind the ear) k. Animal versus human skin - animal skin is more permeable compared to human skin
33
What determines potency? What is the order of potency for external application products?
Drug class not drug % ointment>cream>lotion>gel>foam/spray/solution
34
Can tolerance occur on topical corticosteroids
Yes
35
What is FTU and how is it used for dosing topical preparations
FTU = fingertip unit 1 FTU=0.5g cream = treats 2% body surface area Rule of hand= 4 hand areas=2 FTU = 1g cream
36
Define rheology and viscosity
Rheology - study of changes in form, shape and flow Viscosity - resistance to flow
37
Describe Newtonian and non-Newtonian flow behaviour
Newtonian flow: flow in which viscosity is a constant value viscosity doesn’t change with the force applied to it - one point determination (graph) - Ex. water, alcohol, glycerol Non-Newtonian flow: Flow in which viscosity is NOT a constant value → viscosity changes with the force applied to it - viscosity changes with shear rate - Determination at more than 1 shear rate - Ex. plastic flow, pseudoplastic flow, dilatant flow
38
What are the types of non-newtonian systems and affect on shear stress and viscosity it has. (3) And examples
1. Plastic flow (bingham flow) - need a critical value of shear stress (yield value) - will have shear thinning (viscosity decrease) Ex. flocculated sus, ointments, cream 2. Pseudoplastic flow - No yield value for shear stress (will plateu) - Shear thinning: decrease viscosity while increase shear rate Ex. polymers, gelatin, methylcellulose 3. Dilatant flow - Exponential shear stress - Shear thickening for viscosity Ex. deflocculated sus.
39
Define thixotropy
- Reversible - Time-dependent decrease in apparent viscosity

PHARM 124 Final (3 decks)

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