Collodions are the liquid preparations meant for external application to the skin. They are easy to apply on small cuts and abrasions. They are used when prolonged contact between the skin and the medicament is required. The vehicle used is volatile and it evaporates on application to skin, leaving a flexible, protective film covering at the site of application. Collodions are applied with a brush or rod. Collodion is a flammable, solution of pyroxylin, that is nitrocellulose in ether and alcohol. Collodions are of two types, namely flexible and non-flexible collodions. Flexible collodions are often used as a surgical dressing or to hold dressings in place. When painted on the skin, collodion dries to form a flexible cellulose film. While it is initially colorless, it discolors over time. Non-flexible collodion is used in theatrical makeup.

Properties of Collodions

The following are some important properties of collodions:

1. They should not irritate the tissue of the wound and must be free of antigens.
2. The wound covering must be elastic to ensure that all layers constituting it are in close contact with the wound surface.
3. The collodion must be flexible.

Example

Simple collodion

Nitrocellulose—Film former

Castor oil—Plasticizer

Alcohol—Vehicle

Solvent ether—Vehicle

The following are some examples of official collodion:

1. Collodion USP is a clear or slightly opalescent viscous liquid prepared by dissolving 4% w/v pyroxillin in 3:1 mixture of ether and alcohol.
2. Flexible collodion USP is prepared by adding 2% of camphor and 3% castor oil to the collodion.
3. Salicylic acid collodion USP is 10% solution of salicylic acid in flexible collodion. It is used for its keratolytic effect especially in the removal of corns from the toes. It is also called as “corn solvent.”