*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.
