Local acting substances

&Chelating agents

Dr Sameh AM Abdelghany

Mansoura Faculty of medicineClinical Pharmacology Department

Local acting Substances

Definition substances used mainly for their local

actions. act by mechanical, physical and/or

medical basis of action.

Emollients

CounterirritantsIrritants

Types

Melanizing Demenizing

AdsorbentsDemulcents

Astringents

Keratolytics

I- DEMULCENTS

Definition: are inert substances of high MW

applied over injured skin or mucous membranes to protect them by forming sticky, viscid layer.

Examples: egg white, milk, honey, licorice, and

glycerin.Uses: oTreatment of conjunctivitis oTreatment gastroenteritis e.g. milk in

peptic ulcer

II- Emollients Definition: are fats or oils used to soften the skin

and prevent its dryness.Examples: olive oil, liquid paraffin, and cocoa

butter.Uses: To soften skin and prevent its

dryness.

III- AdsorbentsDefinition: are insoluble powders that can

adsorb water and toxins on their surfaces.

Examples: talk powder, activated charcoal,

kaolin, pectin, etc.

www.themegallery.com

Uses:1. Treatment of diarrhea (kaolin and

pectin).2. Treatment of alkaloid poisoning e.g.

morphine poisoning (activated charcoal).

3. Prevention of napkin dermatitis (to adsorb moisture) e.g. talk powder.

www.themegallery.com

IV- ASTRINGENTSDefinition: are substances that precipitate

surface proteins to form protective layer over injured skin and mucous membranes.

Examples: alcohol, tannic acid, silver nitrate, and

zinc sulfate.

Uses:1. Treatment of burns, wounds, ulcers

and conjunctivitis (zinc sulfate).2. To stop surface bleeding (silver

nitrate).

V- Irritants Definition: substances produce irritation of skin by

local or reflex action. According to the degree of irritation, they classified into:

i. Rubefacients: they produce hyperemia of the skinii. Caustics: they produce destruction of the tissue at

the site of application.

Examples: Physical measures: heat application, short

wave and diathermy. Chemical measures: methyl salicylic acid

and camphor oil. Uses:1. To relief local pain as in arthritis, myositis,

nerve root pain, etc.2. Caustics are used to remove excessive

granulation tissue and in dermabrasion.

VI- Counter-irritantsDefinition: are substances applied to the skin to

produce local and reflex action.i. Local irritant action: → VD and sensation of hotness → psychic effect by diverting the attention of the patient away from the diseased organ.

ii. Reflex action: → stimulation of cutaneous nerve that converges with the visceral nerve at the same spinal segment → block pain sensation.Uses: 1. To relieve pain of arthritis, myositis, or

visceral pain.2. To relieve referred pain.

VII- KeratolyticsDefinition: drugs that soften

keratin and cornified skin.

Examples: salicylic acid.Uses: treatment of warts.

VIII- Melanizing agentsDefinition: drugs that stimulate synthesis

of melanin pigment e.g. khellin.

Uses: treatment of vetilligo.

IX- Demelanizing agentsDefinition: drugs that inhibit synthesis of melanin

pigment.

Uses: treatment of hyperpigmentation.

CHELATING AGENTS

Definition

are organic compounds used to chelate and eliminate metal ions by forming non-toxic complexes with them.

Dimercaprol (BAL): it contains 2 -SH groups that combine

with heavy metals and prevent them to combine with SH-containing enzymes in the body.

Uses: arsenic, mercury, and antimony poisoning.

d-penicillamine

similar to BAL but has one SH group.

Uses: 1. To chelate copper in Wilson’s disease.2. To chelate zinc in rheumatoid arthritis.

Ethylene diamine tetraacetic acid (EDTA)

can chelate Ca++ and lead.

Desferroxamine: chelate iron.