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84 Cards in this Set

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Name types of skin Prep.
­ Transdermal drug delivery systems
­ ointments, creams, lotions
­ topical solutions, tinctures
­ pastes, liniments, topical powders
­ aerosols and Other Preparations
For what reason are preparation applied to the skin?
1. either for their physical effects (skin protectants, lubricants, emollients, drying agents) or
2. for the specific effect of the medicinal agents present (skin infections, itching, burns, diaper rash,acne, psoriasis, eczema etc).
Defn Percutaneous absorption
The absorption of substances from outside the skin to inside the skin into the blood stream is called percutaneous absorption.
WAht are percutaneous absorptions dependant on?
drug substance,
formulation factors and
condition of the skin.
What is the consistency of the skin?
­ sebum
­ sweat gland
­ horney layer or stratum corneum.
The horney layer is a semipermeable membrane about 10-15 μm thick.
It consists of: Keratin (protein) 40%
Water 40%
Triglyceride (lipid). 20%
Name the layers beneath the stratum corneum.
­ stratum germinativum
­ Dermis or the true skin.
Penetration of the skin by Drugs
­ hair follicles
­ sweat glands
­ sebaceous gland and
­ between the cells of horney layer or stratum corneum (main avenue):
- direct penetration thru stratum corneum
- penetrates by passive diffusion
- dependent on concentration, solubility and kp.
Factors affecting Percutaneous absorption
­ Nature of the drug
­ Nature of the vehicle
­ The condition of the skin
­ The presence of moisture
other factors affecting the penetration of the skin
1. Concentration.
2. Surface area.
3. Physicochemical attraction to the skin.
4. Occlusive character of the vehicle.
5. Hydration of the vehicle.
6. Rubbing or inunction.
7. Callused or thickened sites.
8. Period of time of contact with the skin.
9. Multiple application vs single bolus application.
Give some example of Percutaneous enhancers
surfactants, azone, dimethylsulfoxide (DMSO), dimethylacetamide, dimethylformamide, alcohol, acetone, propylene glycol and polyethylene glycol.
What is the mechanism of action of enhancers
1) alteration of the physicochemical properties of stratum corneum.
2) alteration of the hydration of the stratum corneum
3) effecting a change in the structure of the lipids.
4) through solvent action or denaturation
5) carrier mechanisms in the transport of ionizable drugs.
Iontophoresis
­ a physical method
­ delivery of charged compounds using an applied electrical field
­ Examples include lidocaine, amino acids/peptides/insulin, verapamil and propanolol.
Sonophoresis
­ a high frequency ultrasound to influence the integrity of stratum corneum.
­ Examples include hydrocortisone, lidocaine and salicylic acid.
Describe the transdermal system
Transdermal drug delivery systems are designed to support the passage of drug substances from the surface of the skin, through its various layers and into the systemic circulation.
Name the two types of transdermal dosing systems
­ those that control the rate of drug delivery to the skin, and
­ those that allow the skin to control the rate of drug absorption.
What are some desirable features of transdermal system?
1. Controlled rate.
2. Possess the proper physicochemical characteristics.
3. Proper occlusion of the skin.
4. Must have a therapeutic advantage.
5. Should be nonirritating and nonsensitizing to the skin.
6. The patch should adhere well to the patient’s skin.
7. should not permit the proliferation of skin bacteria beneath the occlusion.
What are some advantages of transdermal drug delivery system?
1. Avoids GI pH, enzymes, food etc.
2. Vomiting, diarrhea.
3. Avoid first-pass effect.
4. Avoids parenteral therapy.
5. Multi-day therapy with a single application.
6. Terminate drug effect rapidly by removal.
7. Easy identification of medication.
What are some disadvantages of transdermal drug delivery system?
1. Unsuitable for drugs that irritate skin.
2. Only potent drugs are suitable. Drugs requiring high blood levels - difficult to load.
3. Skin condition can change ability to deliver medication/may affect adhesive function.
4. Cost.
Name the two type of technology of Transdermal Delivery systems.
Two types:
1. Monolithic and
2. Membrane-controlled systems.
Monolithics
­ drug matrix layer between backing and frontal layers.
­ matrix layer drug is dispersed in polymeric material.
­ polymer controls rate of release.
Give some examples of monolithic systems
Nitro-Dur (Key) and Nitrodisc (Searle) are examples of monolithic systems.
What is contained in a membrane controlled Reservoir?
­ contains a drug reservoir and a rate controlling membrane.
- Four layers: backing membrane - mechanical support
Polymer layer - reservoir
Microporous membrane
Adhesive film
Give some example of membrane controlled reservoir
­ Transderm-V (CIBA), a membrane controlled reservoir system, scopolamine for motion sickness.
­ Nitroglycerin: often administered sublingually for short duration (not optimal for prophylaxis)
­ Transderm-Nitro (CIBA), 24 hr delivery
­ Transdermal Nicotine systems : smoking cessation
­ Estraderm (CIBA) - Estradiol - estrogen replacement
­ Testoderm (Alza) - Testosterone replacement.
What is the advantage of membrane controlled system over monolithic system?
Membrane controlled systems have the advantage over monolithic systems in that as long as the drug solution in the reservoir remains saturated, the release rate of drug through the controlling membrane remains constant.
How are membrance controlled systems prepared?
Membrane controlled system may be prepared by preconstructing the delivery unit, filling the drug reservoir, and sealing, or by a process of lamination, which involves a continuous process of construction, dosing, and sealing.
Where should the patch be applied?
1. Site of selection should be clean, dry and hairless; site of application should be rotated.
2. Should not apply to oily, irritated, cut or abraded skin.
3. Patches may be left on when wet.
What is an ointment?
Ointments (unguents) are semisolid preparations intended for external applications which may be medicated or non-medicated, the latter type being commonly referred to as ointment bases and used as such for their emollient or lubricating effect or used as vehicles in the preparation of medicated ointments.
Name the four classification of Ointment bases
Ointment bases are classified into four general groups:
1. Hydrocarbon bases
2. Absorption bases
3. Water-removable bases
4. Water-soluble bases.
What are some characteristic of Hydrocarbon Bases?
1. are anhydrous (water free)
2. do not absorb water readily
3. insoluble in water
4. not water washable
5. chiefly used for their emollient effect
6. aqueous preparations may be incorporated into them only in small amounts
7. retained on the skin for prolonged periods
8. do not permit the escape of moisture from the skin
9. they act as occlusive dressing
10. do not dry out
Give some examples of hydrocarbon bases
Petrolatum, USP:
Synonyms: yellow Petroleum: Petroleum Jelly
Commercial Product: Vaseline

White Petrolatum, USP:
Synonym: White Petroleum Jelly.
Commercial Product: White Vaseline.

Yellow Ointment, USP:
Synonym: Simple Ointment

White Ointment, USP:

Paraffin:

Mineral oil:
Petrolatum, USP
It is a mixture of semisolid hydrocarbons obtained from petroleum.
Synonyms: yellow Petroleum: Petroleum Jelly
Commercial Product: Vaseline
White Petrolatum, USP:
It is petrolatum that has been decolorized.
Synonym: White Petroleum Jelly.
Commercial Product: White Vaseline.
Yellow Ointment USP
Each 100 g of yellow ointment USP contains 5 g of yellow wax and 95 g of petrolatum
Synonym: Simple Ointment
White Ointment, USP
It contains 5% of White Wax (bleached purified beeswax), and 95% white petrolatum
Parafinn
It is a purified mixture of solid hydrocarbon obtained from petroleum. It is a colorless or white more or less translucent mass that may be used to harden or stiffen oleaginous semisolid ointment bases.
Mineral Oil
It is a mixture of liquid hydrocarbons obtained from petroleum. It is useful in the levigating of substances insoluble in it in the preparation of ointments in oleaginous bases.
What are the two types of Absorption bases?
1. aqueous solutions + base ----> w/o emulsion
e.g., Hydrophilic Petrolatum, Anhyd. Lanolin.
2. w/o emulsions bases –> can incorporate water e.g., Lanolin and cold cream.
What are some characteristed of Absorption Bases?
­ Anhydrous
­ will absorb water
­ insoluble in water
­ not water washable
­ not easily removed from the skin
­ provide a degree of occlusion to the skin but less than the oleaginous bases.
­ useful in incorporating aqueous solutions in oleaginous bases.
Give some examples of Absorption Bases
Hydrophilic Petrolatum: It is composed of cholesterol, stearyl alcohol, white wax, and white petrolatum. It has the ability to absorb water, with the formation of a w/o emulsion.

Anhydrous Lanolin: It may contain no more than 0.25% of water. It is insoluble in water, but mixes without separation with about twice its weight of water. The incorporation of water results in the formation of a w/o emulsion.
Synonym: wool fat
What are the ingredients in Hydrophilic Petrolatum
Cholesterol 30 g
Stearyl Alcohol 30 g
White Wax 80 g
White Petrolatum 860 g
How is Hydrophilic Petrolatum made?
Procedure:
Melt stearyl alcohol + white wax in a steam bath.
Add cholesterol with stirring + white petrolatum
Cool.
Commercial product: Aquaphor
Absorb 3 times water
Lanolin, USP
: It is a semisolid, fatlike substance obtained from the wool of sheep. It is a w/o emulsion that contain about 0.25% water. Additional water may be incorporated into lanolin by mixing.
Synonym: Hydrous wool fat.
Cold Cream
It is a semisolid, white, w/o emulsion prepared with cetyl esters wax, white wax, mineral oil, sodium borate, and purified water. The sodium borate combines with the free fatty acids present in the waxes to form sodium soaps that act as the emulsifiers. It is employed as an emollient and ointment base.
Proprietary absorption base
Aquaphor -
Hydrosorb -
Polysorb -
Qualatum -
What are the characteristics of Water-Removable Bases
­ these are o/w emulsion bases
­ hydrous
­ water washable
­ frequently referred to “water-washable” bases
­ will absorb water
­ may be diluted with water
­ have the ability to absorb serous discharges in dermatologic conditions
What are some examples of water removable bases?
Hydrophilic ointment: As the name suggests, it is water loving. It contains sodium lauryl sulfate as the emulsifying agent, with stearyl alcohol and white petrolatum representing the oleaginous phase of the emulsion and propylene glycol and water representing the aqueous phase. Methylparaben and propylparaben are used as preservatives.
Hydrophilic Ointment, USP
Methyl Paraben 0.25 g
Propyl Paraben 0.15 g
Na-lauryl Sulfate 10 g
Propylene Glycol 120 g
Stearyl Alcohol 250 g
White Petrolatum 250 g
Purified Water 370 g
How do you make Hydrophilic Ointment?
Stearyl alcohol + white Petrolatum --> melt at 75oC.
Other agents dissolved in water are added with stirring
What are characteristics of Water-Soluble Bases?
­ contains only water soluble components
­ water washable
­ commonly referred to as “greaseless” because of the absence of oleaginous materials
­ because they soften greatly with addition of water, aqueous solutions are not effectively incorporated into these bases.
­ they are better used for the incorporation of nonaqueous or solid substances.
Give examples of and the general formula for water soluble bases.
Polyethylene Glycol (PEG) Ointment

The general formula:

PEG 3350 (a solid) 400 g
PEG 400 (a liquid) 600 g

However, if a firmer ointment is required, the formula may be altered to permit up to equal parts of the two ingredients.
How do you select the appropriate bases?
a. Desired release rate.
b. Desired percutaneous absorption.
c. Desired occlusive character.
d. Stability of the drug.
e. Influence of the drug on the consistency.
f. Condition of the patients skin
What are some influences of vehicles on hydration of skin?
a) Oleaginous vehicles │
b) w/o emulsion vehicles │
c) o/w emulsion vehicles │
d) water soluble vehicles
Oleaginous vehicles
even though anhydrous themselves, they act as an occlusive dressing minimizing the loss of water from evaporation.
W/O emulsion vehicles
even though these vehicles form an “oil” layer on the skin, they are less occlusive than oleaginous bases
O/W emulsion Vehicles
these show most variability in permeability to water vapor after topical application. The sequence of events after applying:

o/w system spread on skin —>
continuous layer of emulsion on skin —>
evaporation of water from external phase —>
inversion to w/o emulsion system —>
discontinuous layer of inverted emulsion on skin.
O/W system spread on skin
Continuous layer of emulsion on skin —> evaporation of water from external phase —> inversion to w/o emulsion system —> discontinuous layer of inverted emulsion on skin.
water soluble vehicles
these do not wet skin and do not retard evaporation unless applied as a very thick film.
What are some effects of humectants?
­ may dehydrate skin if humidity is low.
­ may interfere with inversion of emulsion to w/o type.
What are some effects of powders in lotions or emulsions?
­ hydrophobic powders.
­ hydrophilic powders.
­ hydrophilic powders will tend to increase water removal from skin.
Factors in Percutaneous Absorptiona) Factors where rate-controlling step is in the skin
i) Major components in skin resistance:
The skin barrier to percutaneous absorption is a “composite membrane” consisting of 3 components:

1) Stratum Corneum - 10 μ
2) Viable or living layers of epidermis - 100 μ
3) Upper part of dermis - 100 μ

Total 210 μ “composite Membrane”.
Diffusion Resistance
Each of the three components of the “composite layer” of the skin has its own resistance to diffusion of substances.
Diffusion resistance for water and octanol and conclusion
For Water:
R, for Stratum cornium/ R, for Epidermis
= 9.1 x106/ 6.3 x103 = 1440

For Octanol:
R, for Stratum cornium/ R, for Epidermis
= 1.18 x105/ 2.08 x103 = 57

Conclusion:
Major barrier to diffusion = Stratum corneum
(polar & non-polar).
Diffusion Rsistance for stratum corneum
For stratum corneum
R, for Water/ R, for octanol = 9.1 x106 / 1.18 x105 = 77

Conclusion:
Stratum corneum is more resistant to passage of polar than non-polar molecules.
Diffusion resistance for Epidermis and Dermis
For Epidermis or Dermis:
R, for Water/ R, for Octanol = 6.3 x103/2.08 x103 = 3

Conclusion:
Even in the “viable” layers of the epidermis (or upper part of the dermis) polar molecules are apt to experience more resistance to their diffusion than non-polar molecules.
Molecular Basis for Polar vs. Non-Polar Barrier
­ the site of membrane diffusion resistance, R, is the intracellular region, not the cellular wall.
­ the intracellular region is a two-phase system chemically (lipid and hydrated protein)
­ composed of polar and non-polar regions; thus separate lipid and polar regions can exist in the hydrated tissue.
­ Both polar and non-polar molecules are capable of dissolving separately in these two closely intermingled polar and non-polar networks.
What where found in experiments as far as diffusion is concerned?
Experimental results indicated that the water structure within the hydrated membrane greatly impedes migrating polar molecules, particularly those that possess available hydroxyl groups for hydrogen-bonding. If a molecule is sufficiently lipid soluble, its migration can apparently constrained to lipid regions of the tissue where hydrogen bonding with water structure does not occur to such an extent. Molecular diffusion mechanisms for the extremely polar and extremely non-polar molecules could then be quite different.
What two princles are the Diffusion processes and Fick's First Law of Diffusion based upon?
passive diffusion
- perfect sink condition
Define Fick's First Law of Diffusion.
Steady state of Penetration through skin

= (Pc.D/L)(Cv - Co).A
= Kp.(Cv - Co).A
= 1/R . (Cv - Co).A

Pc = Partition coefficient
= Concn of drug in Barrier/Concn of drug in Vehicle
D = Diffusion coefficient of drug in barrier
L = thickness of barrier
Cv = Concn of dissolved drug in vehicle
Co = Concn of drug on body side of barrier
= 0, if body is “perfect sink”
A = area of skin to which drug-vehicle is applied
Kp = permeability constant
R = “diffusional resistance”
How are ointments prepared?
1) incorporation and
2) fusion
What is involved in incorpoation?
1. mortar with a pestle, or a spatula and an oint. slab.
2. base + powders ----> geometric dilution.
3. mineral oil or glycerin -----> as a levigating agent.
4. solid + solvent (water) ----->incorporate as a soln.
5. Volatile aromatic materials as alcoholic solutions.
What's involved in fusion?
hard wax + liquids (petrolatum, mineral oil) are gently heated together over a water-bath until a melt is produced.
2. Soluble drugs may be added at this point.
3. The melt is removed from the heat and stirred.
4. Heat sensitive or volatile ingredients should be added just prior to the congealing point which is about 35o to 45oC.
How are creams prepared?
1. Both the aqueous phase and the oil phase are heated separately, to somewhere between 60o and 80oC.
2. The “oil phase” should be heated to at least 5o above the m.p. of the highest melting waxy ingredient.
3. The water phase is heated to 5o above the temperature of the oil phase to prevent premature solidification prior to mixing.
4. Water-soluble adjuvants are dissolved in the heated aqueous phase with stirring
5. Nonvolatile oil-soluble ingredients are dissolved in the heated oil phase.
6. The internal phase is gradually added to the external phase and vigorously mixed.
7. Mechanical dispersion techniques may be used to increase the state of dispersion.
How are ointments preserved?
Pseudomonas aeruginosa and Staphylococcus aureus should be controlled in ointments.
2. Some are sterile, others should have acceptable limits for microbial content.
3. Antimicrobial preservatives in ointments:
p-hydroxybenzoates
phenols
benzoic acid
sorbic acid
quaternary ammonium salts and
other compounds.
4. Semi solid preparations must also be protected from the destructive influences of air, light, moisture, and heat, and the possible chemical interactions between the preparation and the container.
How are ointments packaged and stored?
1. Jars: Glass: uncolored, colored green, amber, or blue, or opaque and porcelain-white.
Plastic

Tubes: tin
plastic

­ Tube filled ointments predominate over jar-filled ointments primarily because they are more convenient for the patient.
­ Also, ointments in tubes are less exposed to air and to potential contaminants and are therefore likely to be more stable and to remain efficacious for longer periods of time than ointments packaged in jars.
­ Most ointments must be stored at temperatures below 30oC to prevent the softening and even the liquefying of the base.
Defn a cream
Creams are defined as “viscous liquid or semi-solid emulsions of either the o/w or the w/o type.” Creams are usually employed as emollients or as medicated application to the skin.
Defn a Vanishing cream
So-called “vanishing creams” are generally o/w emulsions containing large percentages of water and stearic acid. After application of the cream, the water evaporates leaving behind a thin residue film of the stearic acid.
Why do patients and physician prefer cream to ointment?
Many patients and physicians prefer creams to ointments. For one thing, they are generally easier to spread, and, in the case of creams of the o/w emulsion type, easier to remove than many ointments.
What is a Paste?
Pastes, like ointments, are intended for external application to the skin. They differ from ointments primarily in that they generally contain a larger percentage of solid material and as a consequence are thicker and stiffer than ointments. Because of their large percentage of solids, pastes are generally more absorptive and less greasy than ointments prepared with the same components.
When are pastes employed?
Pastes are effectively employed to absorb serous secretions from the site of application. Pastes are therefore preferred over ointments are acute lesions that have a tendency toward crusting or oozing. However, because of their stiffness and impenetrability, pastes are not generally suited for application to hairy parts of the body.
Give examples of pastes used today.
Among the few pastes in use today are triamcinolone Acetonide Dental Paste, an anti-inflammatory preparation applied topically to the oral mucus membranes and Zinc Oxide Paste.
What is a lotion?
Lotions are liquid preparations intended for external application to the skin. Most lotions contain finely powdered substances that are insoluble in the dispersion medium and are suspended through the use of suspending agents.
What are lotions used for?
Lotions are intended to be applied to the skin for the protective or therapeutic value of their constituents. Their fluidity permits rapid and uniform application over a wide surface area. Lotions are intended to dry on the skin soon after application, leaving a thin coat of their medicinal components on the skin’s surface.
What's a plaster?
Plasters are solid or semi-solid adhesive masses spread upon a suitable backing material and intended for external application to a part of the body to provide prolonged contact at that site. Among the backing materials used are paper, cotton, felt, linen, muslin, silk, or plastic. The plasters are adhesive at body temperature and may be used to provide protection or mechanical support (non-medicated plasters) or to provide localized or systemic effects (medicated plasters).
Give an example of a plaster
One plaster in general use is salicylic acid plaster and is intended to be placed on areas requiring the removal of horny layers of skin.