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Locally Acting Drugs

Locally acting drugs are applied onto the skin and sometimes  on mucous membranes, the benefits include:

  1. Concentration of drug at site of application is high
  2. Systemic absorption is negligible
  3. Adverse effects are minimum as compared to systemic preparations.
Types of applications
  •       Tinctures
  •       Wet dressings
  •       Lotions
  •       Gels
  •       Aerosols
  •       Powders
  •       Pastes
  •       Creams
  •       Ointments

Tinctures and wet dressings are usually applied over oozing lesions because of drying of lesions and in descending order these preparations are applied over dry thick skin to act as lubricant.

Names of groups
  •       Demulcents
  •       Emolients
  •       Irritants/counter irritants
  •       Antiseborrheics
  •       Astringents
  •       Ectoparasiticides
  •       Anti-acne drugs
  •       Anti-warts drugs
  •       Anti-pigmentation drugs
  •       Sunscreens
  •       Drugs affecting hair growth
  •       Antiseptics/disinfectants
A. Demulcents

Definition

Means to ‘smooth down’. These are protective agents applied over skin to treat irritation.

Examples:-

  •       Gum acacia
  •       Tragacanth
  •       Glycyrrhiza
  •       Synthetic cellulose

-Methyl cellulose

-Carboxy methyl cellulose

  •       Glycerine
  •       Starch

-Barley starch

-Wheat starch

B. Emolients

External protective which provide lubrication.

Examples:-

  •       Animal fat
  •       Vegetable oils:

– Olive oil

– Cotton seed oil

– Corn oil

– Peanut oil

– Theobroma oil

  •       Paraffin

Vegetable oils may be applied over skin to fight dryness to prevent itching due to thick dry skin.

C. Astringents

These are locally applied protein precipitants i.e. when applied over skin, they cause precipitation of proteins present over surface but do not destroy cells. They just cause contraction of tissues and wrinkling of tissues. Females apply astringents over oily skin because of precipitation of superficial proteins, which is helpful especially during summer season.

Examples

Metallic salts

-ZnSO4

-Al subacetate

-ZnO

Vegetables

– Tannic acid

D. Counter Irritants

Those locally acting drugs used over skin cause feeling of hotness and burning so that they mask the pain.

Degrees:

They are of three types:

1.Rubefacients

2.Vesicants/blisters

3.Pustulants

Mechanism of Action

First degree:

When applied to the skin, there is rubfacient effect  with  feeling of heat, leading to dilation by axon reflex  and paralysis of sensory receptors, which cause stimulation of cerebral centers of  perception and consciousness by painful impression.

2nd degree:

Reddened area +inflammation

Plasma escapes  from capillaries more rapidly but cannot escape through the stratum corneum with the result that epidermis is raised producing vesicles.

Third degree:

Diapedesis of leucocytes occurs and a crop of  painful pustules around skin glands form

1. Camphor

2. Black mustard

3.Cantharides

4.Turpentine oil

5.Methyl cellulose

6.Iodine

7.Eucalyptous oil

These are not rubbed as effects appear which are unpleasant.

E. Sclerosing Agents

Agents used to obliterate varicose veins (dilated veins due to lack of valves).

Uses:

1.Obliterate varicose veins

2. Fibrosis of Haemorrhoids

Examples:

Morhuate Na

Na tetradecyle sulfate

Contraindications:

Acute thrombophlebitis

Valvular or deep venous incompetence

F.Caustics and Escharoitics

Topical agents which destroy upper thick layer of skin, and are thus not commonly used.

Examples:

1.Glacial acetic acid

2.Exzicated alum

3.Phenol

4.AgNO3

5.Trichloracetic acid

Uses:

  1. Destroy warts (viral infection causing raised thick layer over skin)
  2. Keratosis
  3. Moles or Hyperplastic tissues
  4. Fungal infections & Eczema
G. Keratolytics

Desquamating agents, can cause desquamation of dermis.

Characteristics:

Softening & removing horny layer of skin

Uses:

1. Fungal infections

2. Warts & Corns

3. Eczema & certain forms of acne

4. Psoriasis (white silvery spots over skin especially over extensor surfaces, knees,  elbows, scalp due to rapid turn over of epidermis.

These agents are applied to reduce thickness.

Examples:

1. Benzoic acid

2. Salicylic acid

3. Resorcinol

4. Tar (applied to patients of psoriasis)

As damage to skin occurs, these are carefully applied to warts especially salicylic acid.

H. Anti-Perspirants and Deodrants

Agents used to decrease formation of sweat are called anti-perspirants

Agents used to decrease smell from areas where sweating occurs are called deodrants.

Agents:

1. Al Chlorohydrate

2. Al Cl3

3. Buffered AlSO4

4. Al Ziriconium

5. Al Formate

6. Methyl Benzethonium Cl

7. Neomycin SO4

Side Effects:

1.Contact dermatitis

2.Inactivated by Soaps

I. Anti Seborrheics

These locally applied drugs are used to decrease seborrheia.

Agents:

1. Quarternary NH4 surfactants

2. Chlorinated phenols

3. Salicylic acid

4. Sulphur

5. Zn pyrithione (Head & Shoulders)

6. Selenium sulphide ( Exsel, Selsun)

7. Tar

J. Ectoparasiticides

Present over skin e.g.

Hair lice (pediculus capitis)

Scabies(sarcoptes scabei) (lies over skin causes itching especially at bed time especially winters)

Lindane

Crotamiton

Sulfur

Permethrin

Malathion

K. Anti Acne Drugs

Management of acne

  •      Topical preparations for acne
  •       Oral antibiotics
  •       Hormonal treatment
  •       Retinoic acid &derivatives
  •       Tretinoin
  •       All-trans-retinoic acid
L. Melanizing Agents

In hypopigmentation caused by vertiligo, TRIOXSALEN is applied over skin but requires direct sunlight for action, patient is asked to sit in sun after applying cream over lesion. Oral preparations are also available, patient is asked to sit in sun after 2 hours of administration.

M. Anti Pigmentation Drugs

Commonly used especially in Melasina for very long time. These preparations contain:

1.Hydroxyquinones (reversible pigmentation)

2. Monobenzene (irreversible pigmentation)

Side Effects

Irritation of skin, patient is asked to apply small quantity gradually increasing strength.

Inactivated by exposure to light, applied before going to bed.

N. Sunscreens

Sunscreens – Absorb UV light.

Chemical compounds:

1.p-aminobenzoic acid

2.Benzophenones

3.Physical sunscreens

PF stands for production factor. Very fair people require up to 15 SPF, below this level are not effective.

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