Topical preparation

Dr. Basavaraj K. Nanjwade M. Pharm., Ph. D

Department of PharmaceuticsFaculty of Pharmacy

Omer Al-Mukhtar UniversityTobruk, Libya.

E-mail: nanjwadebk@gmail.com

2014/05/25 1Faculty of Pharmacy, Omer Al-Mukhtar University, Tobruk, Libya

CONTENTS1. Structure and function of the skin.2. Factors affecting percutaneous absorption.3. Drug-vehicle-skin interaction.4. Dermatological formulations.5. Liquid topical preparations.6. Semi-solid topical preparations.7. Bases used for topical preparations.8. Release of drugs from ointments, creams and

thermodynamics of their diffusion.9. References.

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Structure of the skin

• Epidermis: Stratum corneum (Horny cell layer) Stratum lucidum (Clear layer) Stratum granulosum ( Granular Layer) Stratum spinosum (Prickly layer) Stratum germinativum • Dermis: • Hypodermis or Subcutaneous layer:

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• The human skin comprises three tissue layers: the stratified, avascular, cellular epidermis, the underlying dermis of connective tissue and subcutaneous fat.

• Hairy skin contains hair follicles and sebaceous glands; the glabrous skin of the soles and palms produces a thick epidermis with a compact stratum corneum, but there are no hair follicles or sebaceous glands.

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Structure of the skin

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Structure of the skin

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Structure of the skin

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Structure of the skin

Functions of the Skin• The skin performs many varied functions but here we need

consider only some aspects of its containment and protective roles.

1. Mechanical function2. Protective functiona. Microbiological barrierb. Chemical barrierc. Radiation barrierd. Heat barrier and temperature regulatione. Electrical barrierf. Mechanical shock2014/05/25 Faculty of Pharmacy, Omer Al-Mukhtar University,

Tobruk, Libya 8

Factors affecting percutaneous absorption

Physico chemical properties of parent molecule

Solubility and partition co- efficient

pH condition

Penetrant concentration

Physico chemical properties of drug delivery system

Release characteristic

Composition of drug delivery system

Permeation enhancer used

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Physiological and pathological condition of skin Lipid film Skin hydration Skin temperature Effect of vehicle Pathological injury to skin Biological factors Skin age Thickness of Stratum Corneum Skin condition

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Factors affecting percutaneous absorption

Chronic use of certain drugs

Presence of hair follicles

Blood flow

Regional skin sites

Species difference

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Factors affecting percutaneous absorption

Drug-vehicle-skin interaction

• Patients also tend to favour creams rather than gels or ointments.

• Select a vehicle that promotes healing and does no further damage, as it to apply a therapeutic agent.

• Most vehicles are blended from one or more of three main components-aqueous solvents, powder and oil-together with thickening and emulsifying agents, buffers, antioxidants, preservatis, colours, propelants etc.

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Dermatological formulations

1. Liquid preparations2. Gels (jellies)3. Powders4. Ointments5. Creams6. Pastes7. Aerosols

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Liquid topical preparations• Liquid preparations for external application include simple

soaks or baths, applications, liniments, lotions, paints, varnishes, tinctures, and ear drops.

• A simple soak provides an active ingredient in aqueous solution or suspension, sometimes with water-miscible solvents.

• Gums and gelling agents may vary the consistency, from mobile liquids to stiff ringing gels.

• Bath additives such as Oilatum Emollient deposit a layer of liquid paraffin on the stratum corneum in an attempt to maintain its moisture content by occulsion.

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Semi-solid topical preparations

• Gels (jellies) are two-component semisolid systems rich in liquid.

• Their one characteristic feature is the presence of a continuous structure providing solid like properties.

• In a typical polar gel, a natural or synthetic polymer builds a three-dimensional matrix throughout a hydrophilic liquid.

• Ointments are greasy, semisolid preparations, often anhydrous and containing dissolved or dispersed medicaments.

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Bases used for topical preparations

• Hydrocarbon bases: These usually consist of soft paraffin or mixtures with hard paraffin.

• Fats and fixed-oil bases: Dermatological vehicles have frequently contained fixed oils of vegetable origin, consisting essentially of the mono-, di- and triglycerides of mixtures of saturated and unsaturated fatty acids.

• Silicones bases: Dimethicones, or dimethyl polysiloxanes, have properties similar to hydrocarbon bases.

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• Absorption bases: Absorption bases soak up water to form water-in-oil emulsions while retaining their semisolid consistencies.

• Emulsifying bases: These essentially anhydrous bases contain oil-in-water emulsifying agents which make them miscible with water and so washable or ‘self-emulsifying’.

• Water-soluble bases: Formulators prepare water-soluble bases from mixtures of high and low molecular weight polyethylene glycols (macrogols, carbowaxes)

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Bases used for topical preparations

Release of drugs from ointments, creams

and thermodynamics of their diffusion• Partitioning of the medicament between the emulsion

phases.• The addition of preservatives.• Determination of a true viscosity for the diffusing

molecules in the vehicle.• The possibility of phase inversion or cracking of the

emulsion when applied to the skin.• Drug may also be trapped in the micelles and the gel

and liquid crystalline phases present in the continuous phase.

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THANK YOUe-mail: nanjwadebk@gmail.com

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