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Many drugs can be applied to the skin without entering the blood. how is this fact explained?

User JRW
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While the outer layer of the skin acts a physical barrier, the skin is porous. It's the same reason sweat appears on our skin when we're hot.
User Ironsun
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*A drug administered by the cutaneous route can have one of these three actions:

Local action, superficial: ex. local anesthetic ...

Deep action: ex. anti-inflammatory action ...

Systemic or general action: ex. anti-anginal action

*The skin is a very effective barrier, which limits the number of drugs that can enter the system.

*The factor influencing the penetration of the drugs are:

- Nature and physicochemical properties of P.A: Molecular weight, hydrophilicity, lipophilicity, stability ...

- Formulation of the drug: Excipients lipophilic, hydrophilic, amphiphilic, an absorption promoter

- Nature and condition of the skin, Location, age, thickness (1 to 8 mm ...), vascularization...

*To not penetrate the skin, a drug should have to be of high molecular mass (to be unable to penetrate through the skin tissue), hydrophilic (since the skin is of a lipophilic nature).

*For example, solar creams should not enter the system so the excipients used are hydrophilic in nature.

User PierreD
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