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Rigid foams

What are Rigid foams?
▪ Rigid foams are systems supplied in pressurized cans in which air or other gas is emulsified
in a liquid phase to the point of stiffening
▪ Examples of Rigid foams:
➢ Shaving cream
➢ Whipped cream
➢ Aerolised shaving cream

Additives used in Semi Solid Preparations

Additives are added to any dosage form to improve its quality and to increase its efficiency as well
as to overcome problems present in the products.
Problems of semisolid dosage forms
1. Fat and oil oxidation (vegetable and animal source)……… Add fat antioxidant
2. Water loss from the creams and gels………Add Humectants
3. Bacterial contamination in water containing products……… Add Preservative
4. Poor permeability of some drugs……… Add Permeation enhancer

1.Fat oxidation and antioxidants:
▪ Natural fixed oils and fats are susceptible to oxidation.

That can be prevented by:
i- storing the product in well closed container protected from light and heat
ii-keeping the product at low temperature if possible
iii-Adding fat antioxidants

e.g. propyl gallate, Butlyted Hydroxy Anisol (BHA), Butlyted Hydroxy Toluene (BHT), Vitamin
E
2.Bacterial contamination and preservatives:

• Products containing water are susceptible to microbial contamination
• This could be solved by addition of preservative such as:

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