Tuesday 23 April 2013

Drugs acting on the skin

Drugs acting on the skin

The skin forms a protective layer allover body.
Different drug forms applied on skin, their actions & therapeutic uses depend on their forms, concentration,  & methods of application.
These drugs may be in form of liquids, semi-solids or solids.
According to action of drugs affecting skin, they  classify into:
Counter irritants
Definition: agents which soften, soothe, lubricate & protect skin surface.
Used as vehicles for oily soluble drugs & as protective agents.
Oils, fats or waxes (hydrocarbons) & derivatives.
Fats as lard & wool fat or lanoline.
Fixed oils are liquid except theobroma oil with is solid at room temperature &
Obtained from plants as olive, cotton seed, linseed, or from fish as code liver oil.
Example of an emollient added to teat dips, whose main function is to disinfect the teat, so reducing chance of cracks leading to sores on the teat skin.
Wool fat:
The hydrous form (lanolin) may be used in teat dips as an alternating to glycerine.

Definition: They are protective agents used to decrease irritation of mucous membrane and abraded skin.
It is used singly or together with antiseptics or astringent materials.
Inert powders as chalk, talc powder and starch.
Definition: agents who coagulate protein in secretions on the surface of the skin and forms a protective layer under which, healing can start and also to stop superficial bleeding by coagulation of blood.
They are mildly antiseptic, astringent and protective.  They are applied in dusting powders, lotions or ointments.
zinc oxide
zinc sulphate
zinc carbonate

Counter irritants:
Definition: agents   who produce irritation of unbroken skin to relieve deep pain in muscle, joints, ligaments, tendons, stimulating the sensory nerve endings,
MOA: producing vasodilatation and increase blood flow to the affected part.
According to the severity of a counter irritant, one of the three following stages will occur:
A -Robefacient:
It means 'to make red' and result from irritation which increase circulation. It is the simplest degree of irritation including local vasodilatation, swelling, and redness raise the temperature and produces anodyne effect (pain-relieving).
Examples: Liniments, (camphor, methylsalicylate, turpentine oil and ammonia), tincture iodine and hot fomentation as hot water.
B -Vesicants:
 It is a stronger degree of irritation this damages the capillary system                 and results in serous exudates collecting in the superficial skin layers to form blisters.
Examples: Bin iodide of mercury blister 1: 8 in vaseline or lard and/ or   10 - 30% cantharides ointment.
C- Pustulants:
It is the third stage, where the irritation is so great that the deep layers of the skin are damaged and the blisters are filled with pus (product of cellular destruction)

Examples: Bin-iodide of mercury blister 1:4 or cantharides blisters in higher concentration.
Uses of counter-irritants:
To relief or reduce the rheumatic pain of joints, to remove excessive granulation tissues,
to treat chronic inflammatory condition of limb joints and tendons of horses.
Tincture of iodine 2.5%
is used as rubefacient and 5% as vesicant when repeatedly applied.
It is commonly used either dissolved in oil or in the form of linament together with other ingredients.
as turpentine linament.
Methyl Salicylate:
It is used as anodyne and
rubefacient in the form of ointment at a concentration of 10%.
Ammonium Carbonate or Hydroxide:
Both have a strong pungent odor of ammonia and
may be used with other ingredients as rubefacient.
Turpentine Oil:
when applied on the skin. It dilates the cutaneous blood vessels and is absorbed through the skin, circulates and excreted through the kidneys.
Therefore it should never be used alone as it may cause nephritis.
It is used commonly as compound camphor liniment. This is a rubefacient liniment and becomes a vesicant or blister.

Bin-iodide of Mercury or Mercuric Iodide:

Externally it is rubefacient, vesicant or postulant counter irritant according to its concentration:
1: 40      Rubefacient 
1: 8   Vesicants
1: 4     Pustulant

Definition: agents that destroy tissues, and used to destroy excessive granulation, with the aim of stimulating normal growth and
also used to destroy warts and horn buds in calves.
Examples: Silver nitrate, phenol and antimonytrichloride

Definition: agents that promote the loosening or separation the cornified skin.
Examples:  salicylic acid, benzoic acid and resorcinol.

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