Semisolids and Rheology Flashcards by Denisse E

What is the average thickness of the various skin layers: corneum, epidermis, dermis

Corneum: 10-20um
Epidermis: 200um
Dermis: 1-5mm

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What is the role of the dermis and what components play a role in percutaneous absorption?

Dermis is the site of drug metabolism

Absorption is influenced by blood vessels and appendages

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What are skin appendages?

Sweat glands, sebaceous glands and hair follicles

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Define shunt route

Absorption through the appendages

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Define acid mantle. What is the significance of a pH of 5.5?

Acid mantle: formed by secretions that have a pH of 4.2-5.6 (bacteriostatic and fungistatic
Formulations with a pH of 5.5 are most compatible with the skin since this is the pH of the skin surface.

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What effect does various UV lights have on the skin?

UVB: 290-320nm, burns the skin
UVBA: 320-400nm, less damaging

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How does circulation maintain sink conditions?

Blood circulation takes up drug absorbed into the skin into the systemic circulation, maintaining the high concentration gradient between the formulation and the skin

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Which drugs target the skin surface?

Cosmetic preparations, antibiotics and antifungals

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Which drugs target the stratum corneum?

Emollients and moisturizers, keratolytics

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Which drugs target skin appendages?

Antiperspirants, exfoliants, depilatories, antibiotics and antifungals

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Which drugs target the viable epidermis and dermis?

Topical steroids, local anesthetics, antihistamines, and anticancer drugs

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Define ointments

Semisolid preparations that are hydrophilic or greasy. Mostly anhydrous.

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Define creams. What types of creams are there?

Semisolid preparations that contain both oil and water phase.
O/W and W/O emulsions

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Define pastes.

Semisolid dosage form that contains a large proportion of solids finely dispersed in a fatty vehicle. Very stiff consistency, forms a thick, impermeable layer on the skin

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Define gels

Semisolid dosage form that contains a gelling agent to provide stiffness. Dissolve in water, good for hairy areas.
Water soluble drugs are easily incorporated.

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Which dermatological vehicles (bases) are able to occlude?

Hydrocarbon bases
Absorption bases
Emulsifying bases
Silicone bases
Pastes
W/O emulsions

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Which dermatological vehicles (bases) are water-washable?

O/W emulsions
Gels
Hydrophilic bases
Emulsifying bases (ointments)

What are absorption bases and examples?

Absorption bases are hydrophobic, greasy and anhydrous. Hydrophilic components provide water absorbing properties.
Adding water forms W/O emulsions

What is wool fat and which component is the emulsifier?

Wool fat is anhydrous lanolin, acts as a W/O emulsifier

What is the difference between lanolin and wool fat?

Wool fat: anhydrous

Lanolin: hydrous

What is cold cream and what is the traditional emulsifier for it?

Cold cream is a beeswax-borax system and is a W/O in-situ emulsifier.
Beeswax can be subbed with other waxes

What is vanishing cream and the traditional emulsifier used for it?

An O/W emulsion that forms potassium stearate in situ.

Smooth and easy to apply, leaves no residue

What type of dermatological base can be used on:
Oozing and weeping dermatoses
Dry, scaly skin
Hairy skin

Oozing and weeping dermatoses: liquids, pastes, o/w creams
Dry, scaly skin: ointments, o/w and w/o creams, pastes, liquids
Hairy skin: gels, liquids, creams

What type of dermatological vehicle is preferred to treat acne?

Liquids, gels, creams, o/w emulsions

No occlusive bases

What type of dermatological vehicle is preferred to treat alopecia?

Water or alcohol based liquids, gels, creams

What type of dermatological vehicle is preferred to treat dermatitis/eczema?

creams, lotions | Avoid occlusives, since this is an oozing condition

What type of dermatological vehicle is preferred to treat psoriasis?

occlusives, creams, ointments with plastic wrap

What type of dermatological vehicle is preferred to treat urticaria?

gels, shake lotions, creams. | No occlusives- should be cooling and soothing

What type of dermatological vehicle is preferred to treat herpes simplex?

liquid lotions, PEG, gels | No occlusives-- an oozing condition

What type of dermatological vehicle is preferred to treat corns and calluses?

Occlusives and collodions

What type of dermatological vehicle is preferred to treat athlete's foot?

o/w creams

What is the brick and mortar model and how is it used to explain drug permeation?

Structure of the stratum corneum is described as brick and mortar where bricks are corneocutes and mortar is lipid between the cells. Pathways for drug absorption are intercellular and intracellular

What are the 3 most important parameters in determining the potency of topical corticosteroids?

Chemical structure, concentration and vehicle

Sort vehicles in order of potency and name recommended vehicles on various skin areas

Ointment>cream>lotion>gel>foam/spray/solution Ointments: preferred in treating chronic lesions or young children. Creams: preferred for non-acute dermatoses Lotions: useful for large areas of skin or hairy areas Gels: most useful on hairy or facial areas Foams/sprays/solutions: on scalp and hairy areas. Shouldn't contain alcohol- can sting

What are local side effects of topical corticosteroids?

Skin atrophy, striae, telangiectasia, purpura, hypertrichosis, acne, hypopigmentation, rebound dermatitis, mask fungal infections

What are the systemic side effects of topical corticosteroids?

Hypothalamus-pituitary axis suppression, hyperglycemia, growth retardation in children, glaucoma, hypertension

What is FTU?

FingerTip Unit | 1 FTU=0.5g of cream or ointment=treats 2% of body surface area

Define solid, elastic, viscoelastic, viscous and liquid in terms of viscosity

Solid: applying force won't change the shape Elastic: will return to original shape without application of force Viscoelastic: viscous properties from liquids and elastic properties from solids. Viscous: thicker liquid Liquid: looses shape immediately upon standing

Describe Newtonian and non-Newtonian flow

Newtonian: constant viscosity | Non-Newtonian: viscosity changes with force applied to it.

What is poise?

The tangential force required per unit area to maintain a velocity difference of 1cm/s between two parallel plates separated by a distance of 1cm

What is a rheogram and why is it the only way to understand non-Newtonian flow behaviour?

A graph of flow properties For non-Newtonian fluids, it's not sufficient to measure viscosity at one shear rate since it changes with different shear rates.

What are examples of Newtonian fluids and non-Newtonian fluids

Newtonian: water, alcohol Plastic: flocculated suspension, ointments, creams Pseudoplastic: polymers in solution, dispersions of natural and synthetic gums, tragacanth, alginates, gelatin, methylcellulose Dilatant: deflocculated suspensions, cornstarch in water