biopharmaceutics

1. Lecture (2)
Skin structure and Topical preparation
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2. Skin flora
The human skin is a rich environment for microbes
around 1000 species of bacteria from 19 bacterial phyla
have been found.
There are two main ecological areas:
• In moist places on the body Corynebacteria together
with Staphylococci dominate.
• In dry areas, there is a mixture of species but
dominated by b-Proteobacteria and Flavobacteriales.
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3. Function of skin flora:
•Around 80 % of the resident skin flora is on the surface of the
stratum corneum, the outermost layer of the epidermis.
•Skin flora is usually non-pathogenic, and either commensals (are
not harmful to their host) or mutualistic (offer a benefit).
•The benefits bacteria can offer include preventing transient
pathogenic organisms from colonizing the skin surface,
either by (a) competing for nutrients, (b) secreting chemicals against
them, or (c) stimulating the skin's immune system.
•However, resident microbes can cause skin diseases and enter the
blood system creating life threatening diseases particularly in
immunosuppressed people.
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4. • On non intact skin, such as wounds, the
microorganisms of the resident skin flora may
trigger infections.
•Particularly high concentrations of microorganisms
are found in body regions rich in sebaceous glands,
e.g. scalp, forehead, front of the chest, and the area
between the shoulder blades.
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6. Acid mantle
• The acid mantle is a very fine, slightly acidic film on
the surface of the skin acting as a barrier to
bacteria, viruses and other potential contaminants
that might penetrate the skin.
• It is secreted by sebaceous glands.
• The pH of the skin is between 4.5 and 6.2, so
it is acidic.
• These contaminants and other chemicals are
primarily alkaline in nature .
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7. • Our world is full of different environments, some that can
have an adverse effect on our acid mantle:
•Central heating
•Air conditioning
•UV rays
•Exhaust fumes
•Pollutant
•Dust
• All of the above can create stress on the skin, leading to
irritation, sensitivity and inflammation.
• These toxins break down our natural defence mechanisms,
disturbing the function of epidermis (the outer layer of skin),
• Once these cells are undermined our skin becomes out of
balance, allowing bacteria to find a passageway through the
stratum corneum.
• Fortunately, our acid mantle protects our skin against these
Environmental Conditions.
• Preventing sun damage and bacterial infections.
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Target regions of the skin
• In dermatology, we aim at five main target regions:-
1. Skin surface.
2. Horny layer.
3. Viable epidermis and upper dermis.
4. Skin glands
5. Systemic circulation.

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1- skin surface treatment
We care for the skin surface by using Cosmetic application
by forming a protective layer.
Some examples include:
1. Protective films (ointment and lotions that protect skin
from moisture, air and chemicals).
2. Sunscreens products.
3. Topical antibiotics.
4. Antiseptics.

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2- Horny layer treatment
1- The main therapies aimed at the horny layer improve
emolliency by raising water content (use of emollient).
2- keratolytic agents which are used to treat excessive
accumulation or thickness of stratum corneum.
•Commonly used agent is salicylic acid 4-10%.
3- Topical clotrimazole treat fungal diseases of nails.

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3- Viable epidermis and dermis treatment
We can treat many diseases provided that the
preparation efficiently delivers drug to the receptor to
produce local effect at the area of its application.
However, many drugs do not readily cross the stratum
corneum so either:
a- Use penetration enhancers or
b- Develop pro-drugs which reach the receptor and
release the pharmacologically active fragment.
Examples:
Topical steroidal anti-inflammatory
non- steroidal anti-inflammatory (voltren emulgel)
Anaesthetic drugs (lidocaine ointment).

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4- Skin glands treatment
1-We may reduce axillary wetness by using
antiperspirants e.g. aluminum or other metal salts. (they
classified as drugs as they affect the body function
mainly the sweat glands)
2- In acne, we use benzoyl peroxide & topic antibiotics.
3- Depilatories (preparations which remove hair)
e.g. barium sulphide.

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5- Systemic treatment via percutaneous absorption
• Generally, in some instances, drugs are
applied to the skin for their systemic effects.
• This is called transdermal therapy.
• E.g. Nitroglycerin patch and Nicotine patch

14. Classification of skin dosage forms.
Preparations applied to the skin can be classified into:
1-Liquid dosage forms.
2- Solid dosage forms.
3- Semi solid dosage forms.
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15. 1- Liquid dosage forms
• Liquid dosage forms may exist as solutions ,suspensions
or colloidal dispersions of therapeutic (drug) and
supplementary ingredients (additives) in aqueous,
hydroalcoholic or non aqueous vehicle.
• The term Lotion is a classical definition of an aqueous
preparation containing insoluble materials which is
applied to the skin without friction such as Calamine
lotion.
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2- Solid dosage forms
• They are used as dermatological agents include tablets
and powders intended for the preparation of solutions
and powder packets.
• Solutions prepared from these dosage forms are
employed as wet dressings.
• Such as Permanganate tables used as disinfectant
and mercuric chloride tablets, Once used as a
treatment for syphilis.
• Dusting powders such as talc, zinc oxide and kaolin,
They have the ability to absorb moisture so keep the
skin surface dry.

17. 3- Semi- Solid dosage forms
• All those preparations applied to cutaneous tissues,
These dosage forms include the classical ointments ,
pastes ,creams ,plasters and poultices
•
Drawing of the application of a poultice to the arm
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Important considerations in the formulation of a dermatological
preparations are
1- Degree of stiffness.
2- Ease of flow.
3- Adhesiveness upon application to the skin.
• Since flow properties significantly differentiate
between the various dermatological dosage forms
their rheology can supply the basis for meaningful
definitions.

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Common semi-solid dosage forms
1- Lotions:
• It is a fluid preparation showing essentially
Newtonian flow characteristics.
•When applied to the skin, it offers no resistance
( yield value) and it flows under force of gravity.

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Common semisolid dosage forms
2- Cream:
•is a semisolid preparation showing essentially pseudoplastic flow
properties.
•when applied creams have very yield value, but will not flow under the
influence of gravity.
•However, a small additional amount of force will readily produce flow.
• It is usually oil in water or water in oil emulsion containing solution or
suspension of the medicinal agent.
•Creams are usually employed as emollient or as medicated applications
to the skin.

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3- An ointment:
• is semisolid preparation which shows plastic flow characteristics .
• When the ointment is applied , there is a definite yield value and
the resistance to flow drops as the applications to the skin is
continued.
• Ointment intended to applied to the eye is known as ophthalmic
ointments.
• Ointment may be medicated or non-medicated (ointment base,
used as lubricant or emollient effect or as a base in the preparation
of medicated ointment)

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4- Gels:
• are semisolid systems that consist of either suspensions of small
inorganic particles or large organic molecules interpenetrated by a
liquid.
• Gels can be either:
1- water based (aqueous gels , water act as swelling agent) or
2- organic solvent based (organogels).

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• 5 - Paste :
• are semisolid dosage forms that contain one or more
drug substances incorporated in a base with large
proportions of finely dispersed solids.
• are intended for external application to skin, but very
thick & stiff.

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1- Cerates:
Definition: waxy, ointment like dosage form.
Application: not intended to melt at body temp but intended to be melted
and spread on a piece of cloth, then applied to the affected area.

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2- Plasters:
Definition: a non waxy dosage form , its usually formed as a piece of cloth,
carrying the drug and applied to the affected area.
Application: it is with self-adhesive properties
Uses: for protection, mechanical support, and to increase the contact with
the drug
E.g. Capsicum plaster (counter irritant)
3- Cataplasms = poultices
Definition: not waxy, past like dosage form, with high solid content.
Application: intended to be warmed and applied directly to the affected
area.
Uses: anti- inflammatory, to draw pus from boils, antiseptic.
But it is not commonly used by humans nowadays, however it is more
common in veterinary medicine.