PASTES - PHARMACEUTICS II (Dispensing Pharmacy) D. Pharm 2nd year PDF Notes

PASTES

Pastes are semi-solid preparations intended for external application to the skin. The pastes are generally very thick and stiff. They do not melt at ordinary temperature and thus form a protective coating over the area where they are applied. They are used mainly as antiseptic protective or soothing dressings which are often spread on lint before being applied.

Bases used for pastes:

The following types of bases are used for the preparation of pastes:

1) Hydrocarbon bases: Soft paraffin and liquid paraffin are commonly used bases for the preparation of pastes.

2) Water miscible bases: Emulsifying ointment is used as a water miscible base for the preparation of pastes. Glycerine is also used as water miscible base for the preparation of pastes.

3) Water soluble bases: Suitable combination of high and low molecular weight polyethylene glycols are mixed together to get product of desired consistency which soften or melt when applied to the skin. Ex: macrogol base.

Method of preparation of pastes:

Pastes are prepared by trifurcations and fusion methods just like ointments. The trituration method is used only in those cases where the base is liquid or semi-solid. The fusion method is used when the base is semi solid or solid in nature.

Storage of pastes:

The pastes should be stored in a well closed container and in a cool place so as to prevent evaporation of moisture present in the paste. Pastes should be stored and supplied in containers made up of materials which do not allow absorption or diffusion of the contents.

Differentiation between pastes and ointments:

Pastes

Ointments

1. They contain large amount of finely powdered solids such as starch, zinc oxide, calcium carbonate etc.

2. They are very thick and stiff.

3. They are less greasy.

4. They are generally applied with a spatula or spread on lint.

5. They form a protective coating to the area where it is applied.

6. Paste contains large amount of powder which is porous in nature, hence perspiration can escape.

7. They are less macerating than ointments.

1. They contain medicaments which are generally dissolved /suspended/emulsified in the base.

2. They are soft semi solid preparations.