08-01-2013, 12:49 PM
Astringents and Lotions
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Astringents
The word "astringent" derives from Latin adstringere, meaning "to bind fast".
Definition: Astringent is a drug that reacts chemically with cellular proteins producing limited coagulation which is accompanied with shrinkage of body tissues.
Astringent protects from external irritation and reduces cellular permeability
It also possesses local styptic and local antiseptic actions
Emulsions: Lotions and Creams
What is a lotion ?
It is a biphasic system of immiscible phases stabilized by a surface active agent
What is the difference between creams and lotions?
If emulsions are liquid, they are called lotions
Creams are semisolids and do not flow through an orifice freely under gravitational force
Creams show a thixotropic behaviour
The Oil-in-Water Emulsions
Viscosity of o/w emulsions depends on:
Volume ratio of internal to external phase
Type of lipid used : high m.p. lipophilic compounds increase viscosity – from soft semisolid to solid (E.g. petrolatum or liquid paraffin)
Presence of thickening agents in lipid phase (E.g. cetosteryl alcohol)
Presence of thickening agents in external phase: E.g. carbomer, hydroxypropyl gaur – ultimate means to increase viscosity, may affect spreadability and make the emulsion more tacky in higher amounts
The Multiple Emulsions
These emulsions typically contain about 18% to 23% oil and 3% to 8% lipophilic emulsifier. The continuous oily phase is stabilized with about 0.5% to 0.8% magnesium sulfate
W/O emulsifiers have an HLB less than 6 and are frequently nonionic or polymeric.
O/W emulsifiers have an HLB greater than 15 and are ionic with high interfacial activity.
For o/w/o multiple emulsions, w/o emulsifiers have an HLB less than 6 with similar properties as a w/o/w w/o emulsifier.